xref: /openbmc/linux/kernel/cgroup/cgroup.c (revision aa1d19f1)
1 /*
2  *  Generic process-grouping system.
3  *
4  *  Based originally on the cpuset system, extracted by Paul Menage
5  *  Copyright (C) 2006 Google, Inc
6  *
7  *  Notifications support
8  *  Copyright (C) 2009 Nokia Corporation
9  *  Author: Kirill A. Shutemov
10  *
11  *  Copyright notices from the original cpuset code:
12  *  --------------------------------------------------
13  *  Copyright (C) 2003 BULL SA.
14  *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
15  *
16  *  Portions derived from Patrick Mochel's sysfs code.
17  *  sysfs is Copyright (c) 2001-3 Patrick Mochel
18  *
19  *  2003-10-10 Written by Simon Derr.
20  *  2003-10-22 Updates by Stephen Hemminger.
21  *  2004 May-July Rework by Paul Jackson.
22  *  ---------------------------------------------------
23  *
24  *  This file is subject to the terms and conditions of the GNU General Public
25  *  License.  See the file COPYING in the main directory of the Linux
26  *  distribution for more details.
27  */
28 
29 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
30 
31 #include "cgroup-internal.h"
32 
33 #include <linux/cred.h>
34 #include <linux/errno.h>
35 #include <linux/init_task.h>
36 #include <linux/kernel.h>
37 #include <linux/magic.h>
38 #include <linux/mutex.h>
39 #include <linux/mount.h>
40 #include <linux/pagemap.h>
41 #include <linux/proc_fs.h>
42 #include <linux/rcupdate.h>
43 #include <linux/sched.h>
44 #include <linux/sched/task.h>
45 #include <linux/slab.h>
46 #include <linux/spinlock.h>
47 #include <linux/percpu-rwsem.h>
48 #include <linux/string.h>
49 #include <linux/hashtable.h>
50 #include <linux/idr.h>
51 #include <linux/kthread.h>
52 #include <linux/atomic.h>
53 #include <linux/cpuset.h>
54 #include <linux/proc_ns.h>
55 #include <linux/nsproxy.h>
56 #include <linux/file.h>
57 #include <linux/fs_parser.h>
58 #include <linux/sched/cputime.h>
59 #include <linux/psi.h>
60 #include <net/sock.h>
61 
62 #define CREATE_TRACE_POINTS
63 #include <trace/events/cgroup.h>
64 
65 #define CGROUP_FILE_NAME_MAX		(MAX_CGROUP_TYPE_NAMELEN +	\
66 					 MAX_CFTYPE_NAME + 2)
67 /* let's not notify more than 100 times per second */
68 #define CGROUP_FILE_NOTIFY_MIN_INTV	DIV_ROUND_UP(HZ, 100)
69 
70 /*
71  * cgroup_mutex is the master lock.  Any modification to cgroup or its
72  * hierarchy must be performed while holding it.
73  *
74  * css_set_lock protects task->cgroups pointer, the list of css_set
75  * objects, and the chain of tasks off each css_set.
76  *
77  * These locks are exported if CONFIG_PROVE_RCU so that accessors in
78  * cgroup.h can use them for lockdep annotations.
79  */
80 DEFINE_MUTEX(cgroup_mutex);
81 DEFINE_SPINLOCK(css_set_lock);
82 
83 #ifdef CONFIG_PROVE_RCU
84 EXPORT_SYMBOL_GPL(cgroup_mutex);
85 EXPORT_SYMBOL_GPL(css_set_lock);
86 #endif
87 
88 DEFINE_SPINLOCK(trace_cgroup_path_lock);
89 char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
90 bool cgroup_debug __read_mostly;
91 
92 /*
93  * Protects cgroup_idr and css_idr so that IDs can be released without
94  * grabbing cgroup_mutex.
95  */
96 static DEFINE_SPINLOCK(cgroup_idr_lock);
97 
98 /*
99  * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
100  * against file removal/re-creation across css hiding.
101  */
102 static DEFINE_SPINLOCK(cgroup_file_kn_lock);
103 
104 struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
105 
106 #define cgroup_assert_mutex_or_rcu_locked()				\
107 	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&			\
108 			   !lockdep_is_held(&cgroup_mutex),		\
109 			   "cgroup_mutex or RCU read lock required");
110 
111 /*
112  * cgroup destruction makes heavy use of work items and there can be a lot
113  * of concurrent destructions.  Use a separate workqueue so that cgroup
114  * destruction work items don't end up filling up max_active of system_wq
115  * which may lead to deadlock.
116  */
117 static struct workqueue_struct *cgroup_destroy_wq;
118 
119 /* generate an array of cgroup subsystem pointers */
120 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
121 struct cgroup_subsys *cgroup_subsys[] = {
122 #include <linux/cgroup_subsys.h>
123 };
124 #undef SUBSYS
125 
126 /* array of cgroup subsystem names */
127 #define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
128 static const char *cgroup_subsys_name[] = {
129 #include <linux/cgroup_subsys.h>
130 };
131 #undef SUBSYS
132 
133 /* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
134 #define SUBSYS(_x)								\
135 	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);			\
136 	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);			\
137 	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);			\
138 	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
139 #include <linux/cgroup_subsys.h>
140 #undef SUBSYS
141 
142 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
143 static struct static_key_true *cgroup_subsys_enabled_key[] = {
144 #include <linux/cgroup_subsys.h>
145 };
146 #undef SUBSYS
147 
148 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
149 static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
150 #include <linux/cgroup_subsys.h>
151 };
152 #undef SUBSYS
153 
154 static DEFINE_PER_CPU(struct cgroup_rstat_cpu, cgrp_dfl_root_rstat_cpu);
155 
156 /*
157  * The default hierarchy, reserved for the subsystems that are otherwise
158  * unattached - it never has more than a single cgroup, and all tasks are
159  * part of that cgroup.
160  */
161 struct cgroup_root cgrp_dfl_root = { .cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu };
162 EXPORT_SYMBOL_GPL(cgrp_dfl_root);
163 
164 /*
165  * The default hierarchy always exists but is hidden until mounted for the
166  * first time.  This is for backward compatibility.
167  */
168 static bool cgrp_dfl_visible;
169 
170 /* some controllers are not supported in the default hierarchy */
171 static u16 cgrp_dfl_inhibit_ss_mask;
172 
173 /* some controllers are implicitly enabled on the default hierarchy */
174 static u16 cgrp_dfl_implicit_ss_mask;
175 
176 /* some controllers can be threaded on the default hierarchy */
177 static u16 cgrp_dfl_threaded_ss_mask;
178 
179 /* The list of hierarchy roots */
180 LIST_HEAD(cgroup_roots);
181 static int cgroup_root_count;
182 
183 /* hierarchy ID allocation and mapping, protected by cgroup_mutex */
184 static DEFINE_IDR(cgroup_hierarchy_idr);
185 
186 /*
187  * Assign a monotonically increasing serial number to csses.  It guarantees
188  * cgroups with bigger numbers are newer than those with smaller numbers.
189  * Also, as csses are always appended to the parent's ->children list, it
190  * guarantees that sibling csses are always sorted in the ascending serial
191  * number order on the list.  Protected by cgroup_mutex.
192  */
193 static u64 css_serial_nr_next = 1;
194 
195 /*
196  * These bitmasks identify subsystems with specific features to avoid
197  * having to do iterative checks repeatedly.
198  */
199 static u16 have_fork_callback __read_mostly;
200 static u16 have_exit_callback __read_mostly;
201 static u16 have_release_callback __read_mostly;
202 static u16 have_canfork_callback __read_mostly;
203 
204 /* cgroup namespace for init task */
205 struct cgroup_namespace init_cgroup_ns = {
206 	.count		= REFCOUNT_INIT(2),
207 	.user_ns	= &init_user_ns,
208 	.ns.ops		= &cgroupns_operations,
209 	.ns.inum	= PROC_CGROUP_INIT_INO,
210 	.root_cset	= &init_css_set,
211 };
212 
213 static struct file_system_type cgroup2_fs_type;
214 static struct cftype cgroup_base_files[];
215 
216 static int cgroup_apply_control(struct cgroup *cgrp);
217 static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
218 static void css_task_iter_advance(struct css_task_iter *it);
219 static int cgroup_destroy_locked(struct cgroup *cgrp);
220 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
221 					      struct cgroup_subsys *ss);
222 static void css_release(struct percpu_ref *ref);
223 static void kill_css(struct cgroup_subsys_state *css);
224 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
225 			      struct cgroup *cgrp, struct cftype cfts[],
226 			      bool is_add);
227 
228 /**
229  * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
230  * @ssid: subsys ID of interest
231  *
232  * cgroup_subsys_enabled() can only be used with literal subsys names which
233  * is fine for individual subsystems but unsuitable for cgroup core.  This
234  * is slower static_key_enabled() based test indexed by @ssid.
235  */
236 bool cgroup_ssid_enabled(int ssid)
237 {
238 	if (CGROUP_SUBSYS_COUNT == 0)
239 		return false;
240 
241 	return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
242 }
243 
244 /**
245  * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
246  * @cgrp: the cgroup of interest
247  *
248  * The default hierarchy is the v2 interface of cgroup and this function
249  * can be used to test whether a cgroup is on the default hierarchy for
250  * cases where a subsystem should behave differnetly depending on the
251  * interface version.
252  *
253  * The set of behaviors which change on the default hierarchy are still
254  * being determined and the mount option is prefixed with __DEVEL__.
255  *
256  * List of changed behaviors:
257  *
258  * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
259  *   and "name" are disallowed.
260  *
261  * - When mounting an existing superblock, mount options should match.
262  *
263  * - Remount is disallowed.
264  *
265  * - rename(2) is disallowed.
266  *
267  * - "tasks" is removed.  Everything should be at process granularity.  Use
268  *   "cgroup.procs" instead.
269  *
270  * - "cgroup.procs" is not sorted.  pids will be unique unless they got
271  *   recycled inbetween reads.
272  *
273  * - "release_agent" and "notify_on_release" are removed.  Replacement
274  *   notification mechanism will be implemented.
275  *
276  * - "cgroup.clone_children" is removed.
277  *
278  * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
279  *   and its descendants contain no task; otherwise, 1.  The file also
280  *   generates kernfs notification which can be monitored through poll and
281  *   [di]notify when the value of the file changes.
282  *
283  * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
284  *   take masks of ancestors with non-empty cpus/mems, instead of being
285  *   moved to an ancestor.
286  *
287  * - cpuset: a task can be moved into an empty cpuset, and again it takes
288  *   masks of ancestors.
289  *
290  * - memcg: use_hierarchy is on by default and the cgroup file for the flag
291  *   is not created.
292  *
293  * - blkcg: blk-throttle becomes properly hierarchical.
294  *
295  * - debug: disallowed on the default hierarchy.
296  */
297 bool cgroup_on_dfl(const struct cgroup *cgrp)
298 {
299 	return cgrp->root == &cgrp_dfl_root;
300 }
301 
302 /* IDR wrappers which synchronize using cgroup_idr_lock */
303 static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
304 			    gfp_t gfp_mask)
305 {
306 	int ret;
307 
308 	idr_preload(gfp_mask);
309 	spin_lock_bh(&cgroup_idr_lock);
310 	ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
311 	spin_unlock_bh(&cgroup_idr_lock);
312 	idr_preload_end();
313 	return ret;
314 }
315 
316 static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
317 {
318 	void *ret;
319 
320 	spin_lock_bh(&cgroup_idr_lock);
321 	ret = idr_replace(idr, ptr, id);
322 	spin_unlock_bh(&cgroup_idr_lock);
323 	return ret;
324 }
325 
326 static void cgroup_idr_remove(struct idr *idr, int id)
327 {
328 	spin_lock_bh(&cgroup_idr_lock);
329 	idr_remove(idr, id);
330 	spin_unlock_bh(&cgroup_idr_lock);
331 }
332 
333 static bool cgroup_has_tasks(struct cgroup *cgrp)
334 {
335 	return cgrp->nr_populated_csets;
336 }
337 
338 bool cgroup_is_threaded(struct cgroup *cgrp)
339 {
340 	return cgrp->dom_cgrp != cgrp;
341 }
342 
343 /* can @cgrp host both domain and threaded children? */
344 static bool cgroup_is_mixable(struct cgroup *cgrp)
345 {
346 	/*
347 	 * Root isn't under domain level resource control exempting it from
348 	 * the no-internal-process constraint, so it can serve as a thread
349 	 * root and a parent of resource domains at the same time.
350 	 */
351 	return !cgroup_parent(cgrp);
352 }
353 
354 /* can @cgrp become a thread root? should always be true for a thread root */
355 static bool cgroup_can_be_thread_root(struct cgroup *cgrp)
356 {
357 	/* mixables don't care */
358 	if (cgroup_is_mixable(cgrp))
359 		return true;
360 
361 	/* domain roots can't be nested under threaded */
362 	if (cgroup_is_threaded(cgrp))
363 		return false;
364 
365 	/* can only have either domain or threaded children */
366 	if (cgrp->nr_populated_domain_children)
367 		return false;
368 
369 	/* and no domain controllers can be enabled */
370 	if (cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
371 		return false;
372 
373 	return true;
374 }
375 
376 /* is @cgrp root of a threaded subtree? */
377 bool cgroup_is_thread_root(struct cgroup *cgrp)
378 {
379 	/* thread root should be a domain */
380 	if (cgroup_is_threaded(cgrp))
381 		return false;
382 
383 	/* a domain w/ threaded children is a thread root */
384 	if (cgrp->nr_threaded_children)
385 		return true;
386 
387 	/*
388 	 * A domain which has tasks and explicit threaded controllers
389 	 * enabled is a thread root.
390 	 */
391 	if (cgroup_has_tasks(cgrp) &&
392 	    (cgrp->subtree_control & cgrp_dfl_threaded_ss_mask))
393 		return true;
394 
395 	return false;
396 }
397 
398 /* a domain which isn't connected to the root w/o brekage can't be used */
399 static bool cgroup_is_valid_domain(struct cgroup *cgrp)
400 {
401 	/* the cgroup itself can be a thread root */
402 	if (cgroup_is_threaded(cgrp))
403 		return false;
404 
405 	/* but the ancestors can't be unless mixable */
406 	while ((cgrp = cgroup_parent(cgrp))) {
407 		if (!cgroup_is_mixable(cgrp) && cgroup_is_thread_root(cgrp))
408 			return false;
409 		if (cgroup_is_threaded(cgrp))
410 			return false;
411 	}
412 
413 	return true;
414 }
415 
416 /* subsystems visibly enabled on a cgroup */
417 static u16 cgroup_control(struct cgroup *cgrp)
418 {
419 	struct cgroup *parent = cgroup_parent(cgrp);
420 	u16 root_ss_mask = cgrp->root->subsys_mask;
421 
422 	if (parent) {
423 		u16 ss_mask = parent->subtree_control;
424 
425 		/* threaded cgroups can only have threaded controllers */
426 		if (cgroup_is_threaded(cgrp))
427 			ss_mask &= cgrp_dfl_threaded_ss_mask;
428 		return ss_mask;
429 	}
430 
431 	if (cgroup_on_dfl(cgrp))
432 		root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
433 				  cgrp_dfl_implicit_ss_mask);
434 	return root_ss_mask;
435 }
436 
437 /* subsystems enabled on a cgroup */
438 static u16 cgroup_ss_mask(struct cgroup *cgrp)
439 {
440 	struct cgroup *parent = cgroup_parent(cgrp);
441 
442 	if (parent) {
443 		u16 ss_mask = parent->subtree_ss_mask;
444 
445 		/* threaded cgroups can only have threaded controllers */
446 		if (cgroup_is_threaded(cgrp))
447 			ss_mask &= cgrp_dfl_threaded_ss_mask;
448 		return ss_mask;
449 	}
450 
451 	return cgrp->root->subsys_mask;
452 }
453 
454 /**
455  * cgroup_css - obtain a cgroup's css for the specified subsystem
456  * @cgrp: the cgroup of interest
457  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
458  *
459  * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
460  * function must be called either under cgroup_mutex or rcu_read_lock() and
461  * the caller is responsible for pinning the returned css if it wants to
462  * keep accessing it outside the said locks.  This function may return
463  * %NULL if @cgrp doesn't have @subsys_id enabled.
464  */
465 static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
466 					      struct cgroup_subsys *ss)
467 {
468 	if (ss)
469 		return rcu_dereference_check(cgrp->subsys[ss->id],
470 					lockdep_is_held(&cgroup_mutex));
471 	else
472 		return &cgrp->self;
473 }
474 
475 /**
476  * cgroup_tryget_css - try to get a cgroup's css for the specified subsystem
477  * @cgrp: the cgroup of interest
478  * @ss: the subsystem of interest
479  *
480  * Find and get @cgrp's css assocaited with @ss.  If the css doesn't exist
481  * or is offline, %NULL is returned.
482  */
483 static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
484 						     struct cgroup_subsys *ss)
485 {
486 	struct cgroup_subsys_state *css;
487 
488 	rcu_read_lock();
489 	css = cgroup_css(cgrp, ss);
490 	if (!css || !css_tryget_online(css))
491 		css = NULL;
492 	rcu_read_unlock();
493 
494 	return css;
495 }
496 
497 /**
498  * cgroup_e_css_by_mask - obtain a cgroup's effective css for the specified ss
499  * @cgrp: the cgroup of interest
500  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
501  *
502  * Similar to cgroup_css() but returns the effective css, which is defined
503  * as the matching css of the nearest ancestor including self which has @ss
504  * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
505  * function is guaranteed to return non-NULL css.
506  */
507 static struct cgroup_subsys_state *cgroup_e_css_by_mask(struct cgroup *cgrp,
508 							struct cgroup_subsys *ss)
509 {
510 	lockdep_assert_held(&cgroup_mutex);
511 
512 	if (!ss)
513 		return &cgrp->self;
514 
515 	/*
516 	 * This function is used while updating css associations and thus
517 	 * can't test the csses directly.  Test ss_mask.
518 	 */
519 	while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
520 		cgrp = cgroup_parent(cgrp);
521 		if (!cgrp)
522 			return NULL;
523 	}
524 
525 	return cgroup_css(cgrp, ss);
526 }
527 
528 /**
529  * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
530  * @cgrp: the cgroup of interest
531  * @ss: the subsystem of interest
532  *
533  * Find and get the effective css of @cgrp for @ss.  The effective css is
534  * defined as the matching css of the nearest ancestor including self which
535  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
536  * the root css is returned, so this function always returns a valid css.
537  *
538  * The returned css is not guaranteed to be online, and therefore it is the
539  * callers responsiblity to tryget a reference for it.
540  */
541 struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
542 					 struct cgroup_subsys *ss)
543 {
544 	struct cgroup_subsys_state *css;
545 
546 	do {
547 		css = cgroup_css(cgrp, ss);
548 
549 		if (css)
550 			return css;
551 		cgrp = cgroup_parent(cgrp);
552 	} while (cgrp);
553 
554 	return init_css_set.subsys[ss->id];
555 }
556 
557 /**
558  * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
559  * @cgrp: the cgroup of interest
560  * @ss: the subsystem of interest
561  *
562  * Find and get the effective css of @cgrp for @ss.  The effective css is
563  * defined as the matching css of the nearest ancestor including self which
564  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
565  * the root css is returned, so this function always returns a valid css.
566  * The returned css must be put using css_put().
567  */
568 struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
569 					     struct cgroup_subsys *ss)
570 {
571 	struct cgroup_subsys_state *css;
572 
573 	rcu_read_lock();
574 
575 	do {
576 		css = cgroup_css(cgrp, ss);
577 
578 		if (css && css_tryget_online(css))
579 			goto out_unlock;
580 		cgrp = cgroup_parent(cgrp);
581 	} while (cgrp);
582 
583 	css = init_css_set.subsys[ss->id];
584 	css_get(css);
585 out_unlock:
586 	rcu_read_unlock();
587 	return css;
588 }
589 
590 static void cgroup_get_live(struct cgroup *cgrp)
591 {
592 	WARN_ON_ONCE(cgroup_is_dead(cgrp));
593 	css_get(&cgrp->self);
594 }
595 
596 /**
597  * __cgroup_task_count - count the number of tasks in a cgroup. The caller
598  * is responsible for taking the css_set_lock.
599  * @cgrp: the cgroup in question
600  */
601 int __cgroup_task_count(const struct cgroup *cgrp)
602 {
603 	int count = 0;
604 	struct cgrp_cset_link *link;
605 
606 	lockdep_assert_held(&css_set_lock);
607 
608 	list_for_each_entry(link, &cgrp->cset_links, cset_link)
609 		count += link->cset->nr_tasks;
610 
611 	return count;
612 }
613 
614 /**
615  * cgroup_task_count - count the number of tasks in a cgroup.
616  * @cgrp: the cgroup in question
617  */
618 int cgroup_task_count(const struct cgroup *cgrp)
619 {
620 	int count;
621 
622 	spin_lock_irq(&css_set_lock);
623 	count = __cgroup_task_count(cgrp);
624 	spin_unlock_irq(&css_set_lock);
625 
626 	return count;
627 }
628 
629 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
630 {
631 	struct cgroup *cgrp = of->kn->parent->priv;
632 	struct cftype *cft = of_cft(of);
633 
634 	/*
635 	 * This is open and unprotected implementation of cgroup_css().
636 	 * seq_css() is only called from a kernfs file operation which has
637 	 * an active reference on the file.  Because all the subsystem
638 	 * files are drained before a css is disassociated with a cgroup,
639 	 * the matching css from the cgroup's subsys table is guaranteed to
640 	 * be and stay valid until the enclosing operation is complete.
641 	 */
642 	if (cft->ss)
643 		return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
644 	else
645 		return &cgrp->self;
646 }
647 EXPORT_SYMBOL_GPL(of_css);
648 
649 /**
650  * for_each_css - iterate all css's of a cgroup
651  * @css: the iteration cursor
652  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
653  * @cgrp: the target cgroup to iterate css's of
654  *
655  * Should be called under cgroup_[tree_]mutex.
656  */
657 #define for_each_css(css, ssid, cgrp)					\
658 	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
659 		if (!((css) = rcu_dereference_check(			\
660 				(cgrp)->subsys[(ssid)],			\
661 				lockdep_is_held(&cgroup_mutex)))) { }	\
662 		else
663 
664 /**
665  * for_each_e_css - iterate all effective css's of a cgroup
666  * @css: the iteration cursor
667  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
668  * @cgrp: the target cgroup to iterate css's of
669  *
670  * Should be called under cgroup_[tree_]mutex.
671  */
672 #define for_each_e_css(css, ssid, cgrp)					    \
673 	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	    \
674 		if (!((css) = cgroup_e_css_by_mask(cgrp,		    \
675 						   cgroup_subsys[(ssid)]))) \
676 			;						    \
677 		else
678 
679 /**
680  * do_each_subsys_mask - filter for_each_subsys with a bitmask
681  * @ss: the iteration cursor
682  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
683  * @ss_mask: the bitmask
684  *
685  * The block will only run for cases where the ssid-th bit (1 << ssid) of
686  * @ss_mask is set.
687  */
688 #define do_each_subsys_mask(ss, ssid, ss_mask) do {			\
689 	unsigned long __ss_mask = (ss_mask);				\
690 	if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */	\
691 		(ssid) = 0;						\
692 		break;							\
693 	}								\
694 	for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {	\
695 		(ss) = cgroup_subsys[ssid];				\
696 		{
697 
698 #define while_each_subsys_mask()					\
699 		}							\
700 	}								\
701 } while (false)
702 
703 /* iterate over child cgrps, lock should be held throughout iteration */
704 #define cgroup_for_each_live_child(child, cgrp)				\
705 	list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
706 		if (({ lockdep_assert_held(&cgroup_mutex);		\
707 		       cgroup_is_dead(child); }))			\
708 			;						\
709 		else
710 
711 /* walk live descendants in preorder */
712 #define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)		\
713 	css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))	\
714 		if (({ lockdep_assert_held(&cgroup_mutex);		\
715 		       (dsct) = (d_css)->cgroup;			\
716 		       cgroup_is_dead(dsct); }))			\
717 			;						\
718 		else
719 
720 /* walk live descendants in postorder */
721 #define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)		\
722 	css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL))	\
723 		if (({ lockdep_assert_held(&cgroup_mutex);		\
724 		       (dsct) = (d_css)->cgroup;			\
725 		       cgroup_is_dead(dsct); }))			\
726 			;						\
727 		else
728 
729 /*
730  * The default css_set - used by init and its children prior to any
731  * hierarchies being mounted. It contains a pointer to the root state
732  * for each subsystem. Also used to anchor the list of css_sets. Not
733  * reference-counted, to improve performance when child cgroups
734  * haven't been created.
735  */
736 struct css_set init_css_set = {
737 	.refcount		= REFCOUNT_INIT(1),
738 	.dom_cset		= &init_css_set,
739 	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),
740 	.mg_tasks		= LIST_HEAD_INIT(init_css_set.mg_tasks),
741 	.task_iters		= LIST_HEAD_INIT(init_css_set.task_iters),
742 	.threaded_csets		= LIST_HEAD_INIT(init_css_set.threaded_csets),
743 	.cgrp_links		= LIST_HEAD_INIT(init_css_set.cgrp_links),
744 	.mg_preload_node	= LIST_HEAD_INIT(init_css_set.mg_preload_node),
745 	.mg_node		= LIST_HEAD_INIT(init_css_set.mg_node),
746 
747 	/*
748 	 * The following field is re-initialized when this cset gets linked
749 	 * in cgroup_init().  However, let's initialize the field
750 	 * statically too so that the default cgroup can be accessed safely
751 	 * early during boot.
752 	 */
753 	.dfl_cgrp		= &cgrp_dfl_root.cgrp,
754 };
755 
756 static int css_set_count	= 1;	/* 1 for init_css_set */
757 
758 static bool css_set_threaded(struct css_set *cset)
759 {
760 	return cset->dom_cset != cset;
761 }
762 
763 /**
764  * css_set_populated - does a css_set contain any tasks?
765  * @cset: target css_set
766  *
767  * css_set_populated() should be the same as !!cset->nr_tasks at steady
768  * state. However, css_set_populated() can be called while a task is being
769  * added to or removed from the linked list before the nr_tasks is
770  * properly updated. Hence, we can't just look at ->nr_tasks here.
771  */
772 static bool css_set_populated(struct css_set *cset)
773 {
774 	lockdep_assert_held(&css_set_lock);
775 
776 	return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
777 }
778 
779 /**
780  * cgroup_update_populated - update the populated count of a cgroup
781  * @cgrp: the target cgroup
782  * @populated: inc or dec populated count
783  *
784  * One of the css_sets associated with @cgrp is either getting its first
785  * task or losing the last.  Update @cgrp->nr_populated_* accordingly.  The
786  * count is propagated towards root so that a given cgroup's
787  * nr_populated_children is zero iff none of its descendants contain any
788  * tasks.
789  *
790  * @cgrp's interface file "cgroup.populated" is zero if both
791  * @cgrp->nr_populated_csets and @cgrp->nr_populated_children are zero and
792  * 1 otherwise.  When the sum changes from or to zero, userland is notified
793  * that the content of the interface file has changed.  This can be used to
794  * detect when @cgrp and its descendants become populated or empty.
795  */
796 static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
797 {
798 	struct cgroup *child = NULL;
799 	int adj = populated ? 1 : -1;
800 
801 	lockdep_assert_held(&css_set_lock);
802 
803 	do {
804 		bool was_populated = cgroup_is_populated(cgrp);
805 
806 		if (!child) {
807 			cgrp->nr_populated_csets += adj;
808 		} else {
809 			if (cgroup_is_threaded(child))
810 				cgrp->nr_populated_threaded_children += adj;
811 			else
812 				cgrp->nr_populated_domain_children += adj;
813 		}
814 
815 		if (was_populated == cgroup_is_populated(cgrp))
816 			break;
817 
818 		cgroup1_check_for_release(cgrp);
819 		TRACE_CGROUP_PATH(notify_populated, cgrp,
820 				  cgroup_is_populated(cgrp));
821 		cgroup_file_notify(&cgrp->events_file);
822 
823 		child = cgrp;
824 		cgrp = cgroup_parent(cgrp);
825 	} while (cgrp);
826 }
827 
828 /**
829  * css_set_update_populated - update populated state of a css_set
830  * @cset: target css_set
831  * @populated: whether @cset is populated or depopulated
832  *
833  * @cset is either getting the first task or losing the last.  Update the
834  * populated counters of all associated cgroups accordingly.
835  */
836 static void css_set_update_populated(struct css_set *cset, bool populated)
837 {
838 	struct cgrp_cset_link *link;
839 
840 	lockdep_assert_held(&css_set_lock);
841 
842 	list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
843 		cgroup_update_populated(link->cgrp, populated);
844 }
845 
846 /**
847  * css_set_move_task - move a task from one css_set to another
848  * @task: task being moved
849  * @from_cset: css_set @task currently belongs to (may be NULL)
850  * @to_cset: new css_set @task is being moved to (may be NULL)
851  * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
852  *
853  * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
854  * css_set, @from_cset can be NULL.  If @task is being disassociated
855  * instead of moved, @to_cset can be NULL.
856  *
857  * This function automatically handles populated counter updates and
858  * css_task_iter adjustments but the caller is responsible for managing
859  * @from_cset and @to_cset's reference counts.
860  */
861 static void css_set_move_task(struct task_struct *task,
862 			      struct css_set *from_cset, struct css_set *to_cset,
863 			      bool use_mg_tasks)
864 {
865 	lockdep_assert_held(&css_set_lock);
866 
867 	if (to_cset && !css_set_populated(to_cset))
868 		css_set_update_populated(to_cset, true);
869 
870 	if (from_cset) {
871 		struct css_task_iter *it, *pos;
872 
873 		WARN_ON_ONCE(list_empty(&task->cg_list));
874 
875 		/*
876 		 * @task is leaving, advance task iterators which are
877 		 * pointing to it so that they can resume at the next
878 		 * position.  Advancing an iterator might remove it from
879 		 * the list, use safe walk.  See css_task_iter_advance*()
880 		 * for details.
881 		 */
882 		list_for_each_entry_safe(it, pos, &from_cset->task_iters,
883 					 iters_node)
884 			if (it->task_pos == &task->cg_list)
885 				css_task_iter_advance(it);
886 
887 		list_del_init(&task->cg_list);
888 		if (!css_set_populated(from_cset))
889 			css_set_update_populated(from_cset, false);
890 	} else {
891 		WARN_ON_ONCE(!list_empty(&task->cg_list));
892 	}
893 
894 	if (to_cset) {
895 		/*
896 		 * We are synchronized through cgroup_threadgroup_rwsem
897 		 * against PF_EXITING setting such that we can't race
898 		 * against cgroup_exit() changing the css_set to
899 		 * init_css_set and dropping the old one.
900 		 */
901 		WARN_ON_ONCE(task->flags & PF_EXITING);
902 
903 		cgroup_move_task(task, to_cset);
904 		list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
905 							     &to_cset->tasks);
906 	}
907 }
908 
909 /*
910  * hash table for cgroup groups. This improves the performance to find
911  * an existing css_set. This hash doesn't (currently) take into
912  * account cgroups in empty hierarchies.
913  */
914 #define CSS_SET_HASH_BITS	7
915 static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
916 
917 static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
918 {
919 	unsigned long key = 0UL;
920 	struct cgroup_subsys *ss;
921 	int i;
922 
923 	for_each_subsys(ss, i)
924 		key += (unsigned long)css[i];
925 	key = (key >> 16) ^ key;
926 
927 	return key;
928 }
929 
930 void put_css_set_locked(struct css_set *cset)
931 {
932 	struct cgrp_cset_link *link, *tmp_link;
933 	struct cgroup_subsys *ss;
934 	int ssid;
935 
936 	lockdep_assert_held(&css_set_lock);
937 
938 	if (!refcount_dec_and_test(&cset->refcount))
939 		return;
940 
941 	WARN_ON_ONCE(!list_empty(&cset->threaded_csets));
942 
943 	/* This css_set is dead. unlink it and release cgroup and css refs */
944 	for_each_subsys(ss, ssid) {
945 		list_del(&cset->e_cset_node[ssid]);
946 		css_put(cset->subsys[ssid]);
947 	}
948 	hash_del(&cset->hlist);
949 	css_set_count--;
950 
951 	list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
952 		list_del(&link->cset_link);
953 		list_del(&link->cgrp_link);
954 		if (cgroup_parent(link->cgrp))
955 			cgroup_put(link->cgrp);
956 		kfree(link);
957 	}
958 
959 	if (css_set_threaded(cset)) {
960 		list_del(&cset->threaded_csets_node);
961 		put_css_set_locked(cset->dom_cset);
962 	}
963 
964 	kfree_rcu(cset, rcu_head);
965 }
966 
967 /**
968  * compare_css_sets - helper function for find_existing_css_set().
969  * @cset: candidate css_set being tested
970  * @old_cset: existing css_set for a task
971  * @new_cgrp: cgroup that's being entered by the task
972  * @template: desired set of css pointers in css_set (pre-calculated)
973  *
974  * Returns true if "cset" matches "old_cset" except for the hierarchy
975  * which "new_cgrp" belongs to, for which it should match "new_cgrp".
976  */
977 static bool compare_css_sets(struct css_set *cset,
978 			     struct css_set *old_cset,
979 			     struct cgroup *new_cgrp,
980 			     struct cgroup_subsys_state *template[])
981 {
982 	struct cgroup *new_dfl_cgrp;
983 	struct list_head *l1, *l2;
984 
985 	/*
986 	 * On the default hierarchy, there can be csets which are
987 	 * associated with the same set of cgroups but different csses.
988 	 * Let's first ensure that csses match.
989 	 */
990 	if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
991 		return false;
992 
993 
994 	/* @cset's domain should match the default cgroup's */
995 	if (cgroup_on_dfl(new_cgrp))
996 		new_dfl_cgrp = new_cgrp;
997 	else
998 		new_dfl_cgrp = old_cset->dfl_cgrp;
999 
1000 	if (new_dfl_cgrp->dom_cgrp != cset->dom_cset->dfl_cgrp)
1001 		return false;
1002 
1003 	/*
1004 	 * Compare cgroup pointers in order to distinguish between
1005 	 * different cgroups in hierarchies.  As different cgroups may
1006 	 * share the same effective css, this comparison is always
1007 	 * necessary.
1008 	 */
1009 	l1 = &cset->cgrp_links;
1010 	l2 = &old_cset->cgrp_links;
1011 	while (1) {
1012 		struct cgrp_cset_link *link1, *link2;
1013 		struct cgroup *cgrp1, *cgrp2;
1014 
1015 		l1 = l1->next;
1016 		l2 = l2->next;
1017 		/* See if we reached the end - both lists are equal length. */
1018 		if (l1 == &cset->cgrp_links) {
1019 			BUG_ON(l2 != &old_cset->cgrp_links);
1020 			break;
1021 		} else {
1022 			BUG_ON(l2 == &old_cset->cgrp_links);
1023 		}
1024 		/* Locate the cgroups associated with these links. */
1025 		link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
1026 		link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
1027 		cgrp1 = link1->cgrp;
1028 		cgrp2 = link2->cgrp;
1029 		/* Hierarchies should be linked in the same order. */
1030 		BUG_ON(cgrp1->root != cgrp2->root);
1031 
1032 		/*
1033 		 * If this hierarchy is the hierarchy of the cgroup
1034 		 * that's changing, then we need to check that this
1035 		 * css_set points to the new cgroup; if it's any other
1036 		 * hierarchy, then this css_set should point to the
1037 		 * same cgroup as the old css_set.
1038 		 */
1039 		if (cgrp1->root == new_cgrp->root) {
1040 			if (cgrp1 != new_cgrp)
1041 				return false;
1042 		} else {
1043 			if (cgrp1 != cgrp2)
1044 				return false;
1045 		}
1046 	}
1047 	return true;
1048 }
1049 
1050 /**
1051  * find_existing_css_set - init css array and find the matching css_set
1052  * @old_cset: the css_set that we're using before the cgroup transition
1053  * @cgrp: the cgroup that we're moving into
1054  * @template: out param for the new set of csses, should be clear on entry
1055  */
1056 static struct css_set *find_existing_css_set(struct css_set *old_cset,
1057 					struct cgroup *cgrp,
1058 					struct cgroup_subsys_state *template[])
1059 {
1060 	struct cgroup_root *root = cgrp->root;
1061 	struct cgroup_subsys *ss;
1062 	struct css_set *cset;
1063 	unsigned long key;
1064 	int i;
1065 
1066 	/*
1067 	 * Build the set of subsystem state objects that we want to see in the
1068 	 * new css_set. while subsystems can change globally, the entries here
1069 	 * won't change, so no need for locking.
1070 	 */
1071 	for_each_subsys(ss, i) {
1072 		if (root->subsys_mask & (1UL << i)) {
1073 			/*
1074 			 * @ss is in this hierarchy, so we want the
1075 			 * effective css from @cgrp.
1076 			 */
1077 			template[i] = cgroup_e_css_by_mask(cgrp, ss);
1078 		} else {
1079 			/*
1080 			 * @ss is not in this hierarchy, so we don't want
1081 			 * to change the css.
1082 			 */
1083 			template[i] = old_cset->subsys[i];
1084 		}
1085 	}
1086 
1087 	key = css_set_hash(template);
1088 	hash_for_each_possible(css_set_table, cset, hlist, key) {
1089 		if (!compare_css_sets(cset, old_cset, cgrp, template))
1090 			continue;
1091 
1092 		/* This css_set matches what we need */
1093 		return cset;
1094 	}
1095 
1096 	/* No existing cgroup group matched */
1097 	return NULL;
1098 }
1099 
1100 static void free_cgrp_cset_links(struct list_head *links_to_free)
1101 {
1102 	struct cgrp_cset_link *link, *tmp_link;
1103 
1104 	list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
1105 		list_del(&link->cset_link);
1106 		kfree(link);
1107 	}
1108 }
1109 
1110 /**
1111  * allocate_cgrp_cset_links - allocate cgrp_cset_links
1112  * @count: the number of links to allocate
1113  * @tmp_links: list_head the allocated links are put on
1114  *
1115  * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
1116  * through ->cset_link.  Returns 0 on success or -errno.
1117  */
1118 static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1119 {
1120 	struct cgrp_cset_link *link;
1121 	int i;
1122 
1123 	INIT_LIST_HEAD(tmp_links);
1124 
1125 	for (i = 0; i < count; i++) {
1126 		link = kzalloc(sizeof(*link), GFP_KERNEL);
1127 		if (!link) {
1128 			free_cgrp_cset_links(tmp_links);
1129 			return -ENOMEM;
1130 		}
1131 		list_add(&link->cset_link, tmp_links);
1132 	}
1133 	return 0;
1134 }
1135 
1136 /**
1137  * link_css_set - a helper function to link a css_set to a cgroup
1138  * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1139  * @cset: the css_set to be linked
1140  * @cgrp: the destination cgroup
1141  */
1142 static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1143 			 struct cgroup *cgrp)
1144 {
1145 	struct cgrp_cset_link *link;
1146 
1147 	BUG_ON(list_empty(tmp_links));
1148 
1149 	if (cgroup_on_dfl(cgrp))
1150 		cset->dfl_cgrp = cgrp;
1151 
1152 	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1153 	link->cset = cset;
1154 	link->cgrp = cgrp;
1155 
1156 	/*
1157 	 * Always add links to the tail of the lists so that the lists are
1158 	 * in choronological order.
1159 	 */
1160 	list_move_tail(&link->cset_link, &cgrp->cset_links);
1161 	list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1162 
1163 	if (cgroup_parent(cgrp))
1164 		cgroup_get_live(cgrp);
1165 }
1166 
1167 /**
1168  * find_css_set - return a new css_set with one cgroup updated
1169  * @old_cset: the baseline css_set
1170  * @cgrp: the cgroup to be updated
1171  *
1172  * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1173  * substituted into the appropriate hierarchy.
1174  */
1175 static struct css_set *find_css_set(struct css_set *old_cset,
1176 				    struct cgroup *cgrp)
1177 {
1178 	struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1179 	struct css_set *cset;
1180 	struct list_head tmp_links;
1181 	struct cgrp_cset_link *link;
1182 	struct cgroup_subsys *ss;
1183 	unsigned long key;
1184 	int ssid;
1185 
1186 	lockdep_assert_held(&cgroup_mutex);
1187 
1188 	/* First see if we already have a cgroup group that matches
1189 	 * the desired set */
1190 	spin_lock_irq(&css_set_lock);
1191 	cset = find_existing_css_set(old_cset, cgrp, template);
1192 	if (cset)
1193 		get_css_set(cset);
1194 	spin_unlock_irq(&css_set_lock);
1195 
1196 	if (cset)
1197 		return cset;
1198 
1199 	cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1200 	if (!cset)
1201 		return NULL;
1202 
1203 	/* Allocate all the cgrp_cset_link objects that we'll need */
1204 	if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1205 		kfree(cset);
1206 		return NULL;
1207 	}
1208 
1209 	refcount_set(&cset->refcount, 1);
1210 	cset->dom_cset = cset;
1211 	INIT_LIST_HEAD(&cset->tasks);
1212 	INIT_LIST_HEAD(&cset->mg_tasks);
1213 	INIT_LIST_HEAD(&cset->task_iters);
1214 	INIT_LIST_HEAD(&cset->threaded_csets);
1215 	INIT_HLIST_NODE(&cset->hlist);
1216 	INIT_LIST_HEAD(&cset->cgrp_links);
1217 	INIT_LIST_HEAD(&cset->mg_preload_node);
1218 	INIT_LIST_HEAD(&cset->mg_node);
1219 
1220 	/* Copy the set of subsystem state objects generated in
1221 	 * find_existing_css_set() */
1222 	memcpy(cset->subsys, template, sizeof(cset->subsys));
1223 
1224 	spin_lock_irq(&css_set_lock);
1225 	/* Add reference counts and links from the new css_set. */
1226 	list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1227 		struct cgroup *c = link->cgrp;
1228 
1229 		if (c->root == cgrp->root)
1230 			c = cgrp;
1231 		link_css_set(&tmp_links, cset, c);
1232 	}
1233 
1234 	BUG_ON(!list_empty(&tmp_links));
1235 
1236 	css_set_count++;
1237 
1238 	/* Add @cset to the hash table */
1239 	key = css_set_hash(cset->subsys);
1240 	hash_add(css_set_table, &cset->hlist, key);
1241 
1242 	for_each_subsys(ss, ssid) {
1243 		struct cgroup_subsys_state *css = cset->subsys[ssid];
1244 
1245 		list_add_tail(&cset->e_cset_node[ssid],
1246 			      &css->cgroup->e_csets[ssid]);
1247 		css_get(css);
1248 	}
1249 
1250 	spin_unlock_irq(&css_set_lock);
1251 
1252 	/*
1253 	 * If @cset should be threaded, look up the matching dom_cset and
1254 	 * link them up.  We first fully initialize @cset then look for the
1255 	 * dom_cset.  It's simpler this way and safe as @cset is guaranteed
1256 	 * to stay empty until we return.
1257 	 */
1258 	if (cgroup_is_threaded(cset->dfl_cgrp)) {
1259 		struct css_set *dcset;
1260 
1261 		dcset = find_css_set(cset, cset->dfl_cgrp->dom_cgrp);
1262 		if (!dcset) {
1263 			put_css_set(cset);
1264 			return NULL;
1265 		}
1266 
1267 		spin_lock_irq(&css_set_lock);
1268 		cset->dom_cset = dcset;
1269 		list_add_tail(&cset->threaded_csets_node,
1270 			      &dcset->threaded_csets);
1271 		spin_unlock_irq(&css_set_lock);
1272 	}
1273 
1274 	return cset;
1275 }
1276 
1277 struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1278 {
1279 	struct cgroup *root_cgrp = kf_root->kn->priv;
1280 
1281 	return root_cgrp->root;
1282 }
1283 
1284 static int cgroup_init_root_id(struct cgroup_root *root)
1285 {
1286 	int id;
1287 
1288 	lockdep_assert_held(&cgroup_mutex);
1289 
1290 	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1291 	if (id < 0)
1292 		return id;
1293 
1294 	root->hierarchy_id = id;
1295 	return 0;
1296 }
1297 
1298 static void cgroup_exit_root_id(struct cgroup_root *root)
1299 {
1300 	lockdep_assert_held(&cgroup_mutex);
1301 
1302 	idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1303 }
1304 
1305 void cgroup_free_root(struct cgroup_root *root)
1306 {
1307 	if (root) {
1308 		idr_destroy(&root->cgroup_idr);
1309 		kfree(root);
1310 	}
1311 }
1312 
1313 static void cgroup_destroy_root(struct cgroup_root *root)
1314 {
1315 	struct cgroup *cgrp = &root->cgrp;
1316 	struct cgrp_cset_link *link, *tmp_link;
1317 
1318 	trace_cgroup_destroy_root(root);
1319 
1320 	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1321 
1322 	BUG_ON(atomic_read(&root->nr_cgrps));
1323 	BUG_ON(!list_empty(&cgrp->self.children));
1324 
1325 	/* Rebind all subsystems back to the default hierarchy */
1326 	WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1327 
1328 	/*
1329 	 * Release all the links from cset_links to this hierarchy's
1330 	 * root cgroup
1331 	 */
1332 	spin_lock_irq(&css_set_lock);
1333 
1334 	list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1335 		list_del(&link->cset_link);
1336 		list_del(&link->cgrp_link);
1337 		kfree(link);
1338 	}
1339 
1340 	spin_unlock_irq(&css_set_lock);
1341 
1342 	if (!list_empty(&root->root_list)) {
1343 		list_del(&root->root_list);
1344 		cgroup_root_count--;
1345 	}
1346 
1347 	cgroup_exit_root_id(root);
1348 
1349 	mutex_unlock(&cgroup_mutex);
1350 
1351 	kernfs_destroy_root(root->kf_root);
1352 	cgroup_free_root(root);
1353 }
1354 
1355 /*
1356  * look up cgroup associated with current task's cgroup namespace on the
1357  * specified hierarchy
1358  */
1359 static struct cgroup *
1360 current_cgns_cgroup_from_root(struct cgroup_root *root)
1361 {
1362 	struct cgroup *res = NULL;
1363 	struct css_set *cset;
1364 
1365 	lockdep_assert_held(&css_set_lock);
1366 
1367 	rcu_read_lock();
1368 
1369 	cset = current->nsproxy->cgroup_ns->root_cset;
1370 	if (cset == &init_css_set) {
1371 		res = &root->cgrp;
1372 	} else {
1373 		struct cgrp_cset_link *link;
1374 
1375 		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1376 			struct cgroup *c = link->cgrp;
1377 
1378 			if (c->root == root) {
1379 				res = c;
1380 				break;
1381 			}
1382 		}
1383 	}
1384 	rcu_read_unlock();
1385 
1386 	BUG_ON(!res);
1387 	return res;
1388 }
1389 
1390 /* look up cgroup associated with given css_set on the specified hierarchy */
1391 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1392 					    struct cgroup_root *root)
1393 {
1394 	struct cgroup *res = NULL;
1395 
1396 	lockdep_assert_held(&cgroup_mutex);
1397 	lockdep_assert_held(&css_set_lock);
1398 
1399 	if (cset == &init_css_set) {
1400 		res = &root->cgrp;
1401 	} else if (root == &cgrp_dfl_root) {
1402 		res = cset->dfl_cgrp;
1403 	} else {
1404 		struct cgrp_cset_link *link;
1405 
1406 		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1407 			struct cgroup *c = link->cgrp;
1408 
1409 			if (c->root == root) {
1410 				res = c;
1411 				break;
1412 			}
1413 		}
1414 	}
1415 
1416 	BUG_ON(!res);
1417 	return res;
1418 }
1419 
1420 /*
1421  * Return the cgroup for "task" from the given hierarchy. Must be
1422  * called with cgroup_mutex and css_set_lock held.
1423  */
1424 struct cgroup *task_cgroup_from_root(struct task_struct *task,
1425 				     struct cgroup_root *root)
1426 {
1427 	/*
1428 	 * No need to lock the task - since we hold cgroup_mutex the
1429 	 * task can't change groups, so the only thing that can happen
1430 	 * is that it exits and its css is set back to init_css_set.
1431 	 */
1432 	return cset_cgroup_from_root(task_css_set(task), root);
1433 }
1434 
1435 /*
1436  * A task must hold cgroup_mutex to modify cgroups.
1437  *
1438  * Any task can increment and decrement the count field without lock.
1439  * So in general, code holding cgroup_mutex can't rely on the count
1440  * field not changing.  However, if the count goes to zero, then only
1441  * cgroup_attach_task() can increment it again.  Because a count of zero
1442  * means that no tasks are currently attached, therefore there is no
1443  * way a task attached to that cgroup can fork (the other way to
1444  * increment the count).  So code holding cgroup_mutex can safely
1445  * assume that if the count is zero, it will stay zero. Similarly, if
1446  * a task holds cgroup_mutex on a cgroup with zero count, it
1447  * knows that the cgroup won't be removed, as cgroup_rmdir()
1448  * needs that mutex.
1449  *
1450  * A cgroup can only be deleted if both its 'count' of using tasks
1451  * is zero, and its list of 'children' cgroups is empty.  Since all
1452  * tasks in the system use _some_ cgroup, and since there is always at
1453  * least one task in the system (init, pid == 1), therefore, root cgroup
1454  * always has either children cgroups and/or using tasks.  So we don't
1455  * need a special hack to ensure that root cgroup cannot be deleted.
1456  *
1457  * P.S.  One more locking exception.  RCU is used to guard the
1458  * update of a tasks cgroup pointer by cgroup_attach_task()
1459  */
1460 
1461 static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1462 
1463 static char *cgroup_fill_name(struct cgroup *cgrp, const struct cftype *cft,
1464 			      char *buf, bool write_link_name)
1465 {
1466 	struct cgroup_subsys *ss = cft->ss;
1467 
1468 	if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1469 	    !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) {
1470 		const char *dbg = (cft->flags & CFTYPE_DEBUG) ? ".__DEBUG__." : "";
1471 
1472 		snprintf(buf, CGROUP_FILE_NAME_MAX, "%s%s.%s",
1473 			 dbg, cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1474 			 write_link_name ? cft->link_name : cft->name);
1475 	} else {
1476 		strscpy(buf, write_link_name ? cft->link_name : cft->name,
1477 			CGROUP_FILE_NAME_MAX);
1478 	}
1479 	return buf;
1480 }
1481 
1482 static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1483 			      char *buf)
1484 {
1485 	return cgroup_fill_name(cgrp, cft, buf, false);
1486 }
1487 
1488 static char *cgroup_link_name(struct cgroup *cgrp, const struct cftype *cft,
1489 			      char *buf)
1490 {
1491 	return cgroup_fill_name(cgrp, cft, buf, true);
1492 }
1493 
1494 /**
1495  * cgroup_file_mode - deduce file mode of a control file
1496  * @cft: the control file in question
1497  *
1498  * S_IRUGO for read, S_IWUSR for write.
1499  */
1500 static umode_t cgroup_file_mode(const struct cftype *cft)
1501 {
1502 	umode_t mode = 0;
1503 
1504 	if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1505 		mode |= S_IRUGO;
1506 
1507 	if (cft->write_u64 || cft->write_s64 || cft->write) {
1508 		if (cft->flags & CFTYPE_WORLD_WRITABLE)
1509 			mode |= S_IWUGO;
1510 		else
1511 			mode |= S_IWUSR;
1512 	}
1513 
1514 	return mode;
1515 }
1516 
1517 /**
1518  * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1519  * @subtree_control: the new subtree_control mask to consider
1520  * @this_ss_mask: available subsystems
1521  *
1522  * On the default hierarchy, a subsystem may request other subsystems to be
1523  * enabled together through its ->depends_on mask.  In such cases, more
1524  * subsystems than specified in "cgroup.subtree_control" may be enabled.
1525  *
1526  * This function calculates which subsystems need to be enabled if
1527  * @subtree_control is to be applied while restricted to @this_ss_mask.
1528  */
1529 static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1530 {
1531 	u16 cur_ss_mask = subtree_control;
1532 	struct cgroup_subsys *ss;
1533 	int ssid;
1534 
1535 	lockdep_assert_held(&cgroup_mutex);
1536 
1537 	cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1538 
1539 	while (true) {
1540 		u16 new_ss_mask = cur_ss_mask;
1541 
1542 		do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1543 			new_ss_mask |= ss->depends_on;
1544 		} while_each_subsys_mask();
1545 
1546 		/*
1547 		 * Mask out subsystems which aren't available.  This can
1548 		 * happen only if some depended-upon subsystems were bound
1549 		 * to non-default hierarchies.
1550 		 */
1551 		new_ss_mask &= this_ss_mask;
1552 
1553 		if (new_ss_mask == cur_ss_mask)
1554 			break;
1555 		cur_ss_mask = new_ss_mask;
1556 	}
1557 
1558 	return cur_ss_mask;
1559 }
1560 
1561 /**
1562  * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1563  * @kn: the kernfs_node being serviced
1564  *
1565  * This helper undoes cgroup_kn_lock_live() and should be invoked before
1566  * the method finishes if locking succeeded.  Note that once this function
1567  * returns the cgroup returned by cgroup_kn_lock_live() may become
1568  * inaccessible any time.  If the caller intends to continue to access the
1569  * cgroup, it should pin it before invoking this function.
1570  */
1571 void cgroup_kn_unlock(struct kernfs_node *kn)
1572 {
1573 	struct cgroup *cgrp;
1574 
1575 	if (kernfs_type(kn) == KERNFS_DIR)
1576 		cgrp = kn->priv;
1577 	else
1578 		cgrp = kn->parent->priv;
1579 
1580 	mutex_unlock(&cgroup_mutex);
1581 
1582 	kernfs_unbreak_active_protection(kn);
1583 	cgroup_put(cgrp);
1584 }
1585 
1586 /**
1587  * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1588  * @kn: the kernfs_node being serviced
1589  * @drain_offline: perform offline draining on the cgroup
1590  *
1591  * This helper is to be used by a cgroup kernfs method currently servicing
1592  * @kn.  It breaks the active protection, performs cgroup locking and
1593  * verifies that the associated cgroup is alive.  Returns the cgroup if
1594  * alive; otherwise, %NULL.  A successful return should be undone by a
1595  * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1596  * cgroup is drained of offlining csses before return.
1597  *
1598  * Any cgroup kernfs method implementation which requires locking the
1599  * associated cgroup should use this helper.  It avoids nesting cgroup
1600  * locking under kernfs active protection and allows all kernfs operations
1601  * including self-removal.
1602  */
1603 struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
1604 {
1605 	struct cgroup *cgrp;
1606 
1607 	if (kernfs_type(kn) == KERNFS_DIR)
1608 		cgrp = kn->priv;
1609 	else
1610 		cgrp = kn->parent->priv;
1611 
1612 	/*
1613 	 * We're gonna grab cgroup_mutex which nests outside kernfs
1614 	 * active_ref.  cgroup liveliness check alone provides enough
1615 	 * protection against removal.  Ensure @cgrp stays accessible and
1616 	 * break the active_ref protection.
1617 	 */
1618 	if (!cgroup_tryget(cgrp))
1619 		return NULL;
1620 	kernfs_break_active_protection(kn);
1621 
1622 	if (drain_offline)
1623 		cgroup_lock_and_drain_offline(cgrp);
1624 	else
1625 		mutex_lock(&cgroup_mutex);
1626 
1627 	if (!cgroup_is_dead(cgrp))
1628 		return cgrp;
1629 
1630 	cgroup_kn_unlock(kn);
1631 	return NULL;
1632 }
1633 
1634 static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1635 {
1636 	char name[CGROUP_FILE_NAME_MAX];
1637 
1638 	lockdep_assert_held(&cgroup_mutex);
1639 
1640 	if (cft->file_offset) {
1641 		struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1642 		struct cgroup_file *cfile = (void *)css + cft->file_offset;
1643 
1644 		spin_lock_irq(&cgroup_file_kn_lock);
1645 		cfile->kn = NULL;
1646 		spin_unlock_irq(&cgroup_file_kn_lock);
1647 
1648 		del_timer_sync(&cfile->notify_timer);
1649 	}
1650 
1651 	kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1652 	if (cft->flags & CFTYPE_SYMLINKED)
1653 		kernfs_remove_by_name(cgrp->kn,
1654 				      cgroup_link_name(cgrp, cft, name));
1655 }
1656 
1657 /**
1658  * css_clear_dir - remove subsys files in a cgroup directory
1659  * @css: taget css
1660  */
1661 static void css_clear_dir(struct cgroup_subsys_state *css)
1662 {
1663 	struct cgroup *cgrp = css->cgroup;
1664 	struct cftype *cfts;
1665 
1666 	if (!(css->flags & CSS_VISIBLE))
1667 		return;
1668 
1669 	css->flags &= ~CSS_VISIBLE;
1670 
1671 	if (!css->ss) {
1672 		if (cgroup_on_dfl(cgrp))
1673 			cfts = cgroup_base_files;
1674 		else
1675 			cfts = cgroup1_base_files;
1676 
1677 		cgroup_addrm_files(css, cgrp, cfts, false);
1678 	} else {
1679 		list_for_each_entry(cfts, &css->ss->cfts, node)
1680 			cgroup_addrm_files(css, cgrp, cfts, false);
1681 	}
1682 }
1683 
1684 /**
1685  * css_populate_dir - create subsys files in a cgroup directory
1686  * @css: target css
1687  *
1688  * On failure, no file is added.
1689  */
1690 static int css_populate_dir(struct cgroup_subsys_state *css)
1691 {
1692 	struct cgroup *cgrp = css->cgroup;
1693 	struct cftype *cfts, *failed_cfts;
1694 	int ret;
1695 
1696 	if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1697 		return 0;
1698 
1699 	if (!css->ss) {
1700 		if (cgroup_on_dfl(cgrp))
1701 			cfts = cgroup_base_files;
1702 		else
1703 			cfts = cgroup1_base_files;
1704 
1705 		ret = cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1706 		if (ret < 0)
1707 			return ret;
1708 	} else {
1709 		list_for_each_entry(cfts, &css->ss->cfts, node) {
1710 			ret = cgroup_addrm_files(css, cgrp, cfts, true);
1711 			if (ret < 0) {
1712 				failed_cfts = cfts;
1713 				goto err;
1714 			}
1715 		}
1716 	}
1717 
1718 	css->flags |= CSS_VISIBLE;
1719 
1720 	return 0;
1721 err:
1722 	list_for_each_entry(cfts, &css->ss->cfts, node) {
1723 		if (cfts == failed_cfts)
1724 			break;
1725 		cgroup_addrm_files(css, cgrp, cfts, false);
1726 	}
1727 	return ret;
1728 }
1729 
1730 int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1731 {
1732 	struct cgroup *dcgrp = &dst_root->cgrp;
1733 	struct cgroup_subsys *ss;
1734 	int ssid, i, ret;
1735 
1736 	lockdep_assert_held(&cgroup_mutex);
1737 
1738 	do_each_subsys_mask(ss, ssid, ss_mask) {
1739 		/*
1740 		 * If @ss has non-root csses attached to it, can't move.
1741 		 * If @ss is an implicit controller, it is exempt from this
1742 		 * rule and can be stolen.
1743 		 */
1744 		if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1745 		    !ss->implicit_on_dfl)
1746 			return -EBUSY;
1747 
1748 		/* can't move between two non-dummy roots either */
1749 		if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1750 			return -EBUSY;
1751 	} while_each_subsys_mask();
1752 
1753 	do_each_subsys_mask(ss, ssid, ss_mask) {
1754 		struct cgroup_root *src_root = ss->root;
1755 		struct cgroup *scgrp = &src_root->cgrp;
1756 		struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1757 		struct css_set *cset;
1758 
1759 		WARN_ON(!css || cgroup_css(dcgrp, ss));
1760 
1761 		/* disable from the source */
1762 		src_root->subsys_mask &= ~(1 << ssid);
1763 		WARN_ON(cgroup_apply_control(scgrp));
1764 		cgroup_finalize_control(scgrp, 0);
1765 
1766 		/* rebind */
1767 		RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1768 		rcu_assign_pointer(dcgrp->subsys[ssid], css);
1769 		ss->root = dst_root;
1770 		css->cgroup = dcgrp;
1771 
1772 		spin_lock_irq(&css_set_lock);
1773 		hash_for_each(css_set_table, i, cset, hlist)
1774 			list_move_tail(&cset->e_cset_node[ss->id],
1775 				       &dcgrp->e_csets[ss->id]);
1776 		spin_unlock_irq(&css_set_lock);
1777 
1778 		/* default hierarchy doesn't enable controllers by default */
1779 		dst_root->subsys_mask |= 1 << ssid;
1780 		if (dst_root == &cgrp_dfl_root) {
1781 			static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1782 		} else {
1783 			dcgrp->subtree_control |= 1 << ssid;
1784 			static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1785 		}
1786 
1787 		ret = cgroup_apply_control(dcgrp);
1788 		if (ret)
1789 			pr_warn("partial failure to rebind %s controller (err=%d)\n",
1790 				ss->name, ret);
1791 
1792 		if (ss->bind)
1793 			ss->bind(css);
1794 	} while_each_subsys_mask();
1795 
1796 	kernfs_activate(dcgrp->kn);
1797 	return 0;
1798 }
1799 
1800 int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1801 		     struct kernfs_root *kf_root)
1802 {
1803 	int len = 0;
1804 	char *buf = NULL;
1805 	struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1806 	struct cgroup *ns_cgroup;
1807 
1808 	buf = kmalloc(PATH_MAX, GFP_KERNEL);
1809 	if (!buf)
1810 		return -ENOMEM;
1811 
1812 	spin_lock_irq(&css_set_lock);
1813 	ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1814 	len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1815 	spin_unlock_irq(&css_set_lock);
1816 
1817 	if (len >= PATH_MAX)
1818 		len = -ERANGE;
1819 	else if (len > 0) {
1820 		seq_escape(sf, buf, " \t\n\\");
1821 		len = 0;
1822 	}
1823 	kfree(buf);
1824 	return len;
1825 }
1826 
1827 enum cgroup2_param {
1828 	Opt_nsdelegate,
1829 	Opt_memory_localevents,
1830 	nr__cgroup2_params
1831 };
1832 
1833 static const struct fs_parameter_spec cgroup2_param_specs[] = {
1834 	fsparam_flag("nsdelegate",		Opt_nsdelegate),
1835 	fsparam_flag("memory_localevents",	Opt_memory_localevents),
1836 	{}
1837 };
1838 
1839 static const struct fs_parameter_description cgroup2_fs_parameters = {
1840 	.name		= "cgroup2",
1841 	.specs		= cgroup2_param_specs,
1842 };
1843 
1844 static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param)
1845 {
1846 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
1847 	struct fs_parse_result result;
1848 	int opt;
1849 
1850 	opt = fs_parse(fc, &cgroup2_fs_parameters, param, &result);
1851 	if (opt < 0)
1852 		return opt;
1853 
1854 	switch (opt) {
1855 	case Opt_nsdelegate:
1856 		ctx->flags |= CGRP_ROOT_NS_DELEGATE;
1857 		return 0;
1858 	case Opt_memory_localevents:
1859 		ctx->flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1860 		return 0;
1861 	}
1862 	return -EINVAL;
1863 }
1864 
1865 static void apply_cgroup_root_flags(unsigned int root_flags)
1866 {
1867 	if (current->nsproxy->cgroup_ns == &init_cgroup_ns) {
1868 		if (root_flags & CGRP_ROOT_NS_DELEGATE)
1869 			cgrp_dfl_root.flags |= CGRP_ROOT_NS_DELEGATE;
1870 		else
1871 			cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE;
1872 
1873 		if (root_flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
1874 			cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1875 		else
1876 			cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1877 	}
1878 }
1879 
1880 static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
1881 {
1882 	if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
1883 		seq_puts(seq, ",nsdelegate");
1884 	if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
1885 		seq_puts(seq, ",memory_localevents");
1886 	return 0;
1887 }
1888 
1889 static int cgroup_reconfigure(struct fs_context *fc)
1890 {
1891 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
1892 
1893 	apply_cgroup_root_flags(ctx->flags);
1894 	return 0;
1895 }
1896 
1897 /*
1898  * To reduce the fork() overhead for systems that are not actually using
1899  * their cgroups capability, we don't maintain the lists running through
1900  * each css_set to its tasks until we see the list actually used - in other
1901  * words after the first mount.
1902  */
1903 static bool use_task_css_set_links __read_mostly;
1904 
1905 static void cgroup_enable_task_cg_lists(void)
1906 {
1907 	struct task_struct *p, *g;
1908 
1909 	/*
1910 	 * We need tasklist_lock because RCU is not safe against
1911 	 * while_each_thread(). Besides, a forking task that has passed
1912 	 * cgroup_post_fork() without seeing use_task_css_set_links = 1
1913 	 * is not guaranteed to have its child immediately visible in the
1914 	 * tasklist if we walk through it with RCU.
1915 	 */
1916 	read_lock(&tasklist_lock);
1917 	spin_lock_irq(&css_set_lock);
1918 
1919 	if (use_task_css_set_links)
1920 		goto out_unlock;
1921 
1922 	use_task_css_set_links = true;
1923 
1924 	do_each_thread(g, p) {
1925 		WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1926 			     task_css_set(p) != &init_css_set);
1927 
1928 		/*
1929 		 * We should check if the process is exiting, otherwise
1930 		 * it will race with cgroup_exit() in that the list
1931 		 * entry won't be deleted though the process has exited.
1932 		 * Do it while holding siglock so that we don't end up
1933 		 * racing against cgroup_exit().
1934 		 *
1935 		 * Interrupts were already disabled while acquiring
1936 		 * the css_set_lock, so we do not need to disable it
1937 		 * again when acquiring the sighand->siglock here.
1938 		 */
1939 		spin_lock(&p->sighand->siglock);
1940 		if (!(p->flags & PF_EXITING)) {
1941 			struct css_set *cset = task_css_set(p);
1942 
1943 			if (!css_set_populated(cset))
1944 				css_set_update_populated(cset, true);
1945 			list_add_tail(&p->cg_list, &cset->tasks);
1946 			get_css_set(cset);
1947 			cset->nr_tasks++;
1948 		}
1949 		spin_unlock(&p->sighand->siglock);
1950 	} while_each_thread(g, p);
1951 out_unlock:
1952 	spin_unlock_irq(&css_set_lock);
1953 	read_unlock(&tasklist_lock);
1954 }
1955 
1956 static void init_cgroup_housekeeping(struct cgroup *cgrp)
1957 {
1958 	struct cgroup_subsys *ss;
1959 	int ssid;
1960 
1961 	INIT_LIST_HEAD(&cgrp->self.sibling);
1962 	INIT_LIST_HEAD(&cgrp->self.children);
1963 	INIT_LIST_HEAD(&cgrp->cset_links);
1964 	INIT_LIST_HEAD(&cgrp->pidlists);
1965 	mutex_init(&cgrp->pidlist_mutex);
1966 	cgrp->self.cgroup = cgrp;
1967 	cgrp->self.flags |= CSS_ONLINE;
1968 	cgrp->dom_cgrp = cgrp;
1969 	cgrp->max_descendants = INT_MAX;
1970 	cgrp->max_depth = INT_MAX;
1971 	INIT_LIST_HEAD(&cgrp->rstat_css_list);
1972 	prev_cputime_init(&cgrp->prev_cputime);
1973 
1974 	for_each_subsys(ss, ssid)
1975 		INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1976 
1977 	init_waitqueue_head(&cgrp->offline_waitq);
1978 	INIT_WORK(&cgrp->release_agent_work, cgroup1_release_agent);
1979 }
1980 
1981 void init_cgroup_root(struct cgroup_fs_context *ctx)
1982 {
1983 	struct cgroup_root *root = ctx->root;
1984 	struct cgroup *cgrp = &root->cgrp;
1985 
1986 	INIT_LIST_HEAD(&root->root_list);
1987 	atomic_set(&root->nr_cgrps, 1);
1988 	cgrp->root = root;
1989 	init_cgroup_housekeeping(cgrp);
1990 	idr_init(&root->cgroup_idr);
1991 
1992 	root->flags = ctx->flags;
1993 	if (ctx->release_agent)
1994 		strscpy(root->release_agent_path, ctx->release_agent, PATH_MAX);
1995 	if (ctx->name)
1996 		strscpy(root->name, ctx->name, MAX_CGROUP_ROOT_NAMELEN);
1997 	if (ctx->cpuset_clone_children)
1998 		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1999 }
2000 
2001 int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
2002 {
2003 	LIST_HEAD(tmp_links);
2004 	struct cgroup *root_cgrp = &root->cgrp;
2005 	struct kernfs_syscall_ops *kf_sops;
2006 	struct css_set *cset;
2007 	int i, ret;
2008 
2009 	lockdep_assert_held(&cgroup_mutex);
2010 
2011 	ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
2012 	if (ret < 0)
2013 		goto out;
2014 	root_cgrp->id = ret;
2015 	root_cgrp->ancestor_ids[0] = ret;
2016 
2017 	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release,
2018 			      0, GFP_KERNEL);
2019 	if (ret)
2020 		goto out;
2021 
2022 	/*
2023 	 * We're accessing css_set_count without locking css_set_lock here,
2024 	 * but that's OK - it can only be increased by someone holding
2025 	 * cgroup_lock, and that's us.  Later rebinding may disable
2026 	 * controllers on the default hierarchy and thus create new csets,
2027 	 * which can't be more than the existing ones.  Allocate 2x.
2028 	 */
2029 	ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
2030 	if (ret)
2031 		goto cancel_ref;
2032 
2033 	ret = cgroup_init_root_id(root);
2034 	if (ret)
2035 		goto cancel_ref;
2036 
2037 	kf_sops = root == &cgrp_dfl_root ?
2038 		&cgroup_kf_syscall_ops : &cgroup1_kf_syscall_ops;
2039 
2040 	root->kf_root = kernfs_create_root(kf_sops,
2041 					   KERNFS_ROOT_CREATE_DEACTIVATED |
2042 					   KERNFS_ROOT_SUPPORT_EXPORTOP,
2043 					   root_cgrp);
2044 	if (IS_ERR(root->kf_root)) {
2045 		ret = PTR_ERR(root->kf_root);
2046 		goto exit_root_id;
2047 	}
2048 	root_cgrp->kn = root->kf_root->kn;
2049 
2050 	ret = css_populate_dir(&root_cgrp->self);
2051 	if (ret)
2052 		goto destroy_root;
2053 
2054 	ret = rebind_subsystems(root, ss_mask);
2055 	if (ret)
2056 		goto destroy_root;
2057 
2058 	ret = cgroup_bpf_inherit(root_cgrp);
2059 	WARN_ON_ONCE(ret);
2060 
2061 	trace_cgroup_setup_root(root);
2062 
2063 	/*
2064 	 * There must be no failure case after here, since rebinding takes
2065 	 * care of subsystems' refcounts, which are explicitly dropped in
2066 	 * the failure exit path.
2067 	 */
2068 	list_add(&root->root_list, &cgroup_roots);
2069 	cgroup_root_count++;
2070 
2071 	/*
2072 	 * Link the root cgroup in this hierarchy into all the css_set
2073 	 * objects.
2074 	 */
2075 	spin_lock_irq(&css_set_lock);
2076 	hash_for_each(css_set_table, i, cset, hlist) {
2077 		link_css_set(&tmp_links, cset, root_cgrp);
2078 		if (css_set_populated(cset))
2079 			cgroup_update_populated(root_cgrp, true);
2080 	}
2081 	spin_unlock_irq(&css_set_lock);
2082 
2083 	BUG_ON(!list_empty(&root_cgrp->self.children));
2084 	BUG_ON(atomic_read(&root->nr_cgrps) != 1);
2085 
2086 	kernfs_activate(root_cgrp->kn);
2087 	ret = 0;
2088 	goto out;
2089 
2090 destroy_root:
2091 	kernfs_destroy_root(root->kf_root);
2092 	root->kf_root = NULL;
2093 exit_root_id:
2094 	cgroup_exit_root_id(root);
2095 cancel_ref:
2096 	percpu_ref_exit(&root_cgrp->self.refcnt);
2097 out:
2098 	free_cgrp_cset_links(&tmp_links);
2099 	return ret;
2100 }
2101 
2102 int cgroup_do_get_tree(struct fs_context *fc)
2103 {
2104 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2105 	int ret;
2106 
2107 	ctx->kfc.root = ctx->root->kf_root;
2108 	if (fc->fs_type == &cgroup2_fs_type)
2109 		ctx->kfc.magic = CGROUP2_SUPER_MAGIC;
2110 	else
2111 		ctx->kfc.magic = CGROUP_SUPER_MAGIC;
2112 	ret = kernfs_get_tree(fc);
2113 
2114 	/*
2115 	 * In non-init cgroup namespace, instead of root cgroup's dentry,
2116 	 * we return the dentry corresponding to the cgroupns->root_cgrp.
2117 	 */
2118 	if (!ret && ctx->ns != &init_cgroup_ns) {
2119 		struct dentry *nsdentry;
2120 		struct super_block *sb = fc->root->d_sb;
2121 		struct cgroup *cgrp;
2122 
2123 		mutex_lock(&cgroup_mutex);
2124 		spin_lock_irq(&css_set_lock);
2125 
2126 		cgrp = cset_cgroup_from_root(ctx->ns->root_cset, ctx->root);
2127 
2128 		spin_unlock_irq(&css_set_lock);
2129 		mutex_unlock(&cgroup_mutex);
2130 
2131 		nsdentry = kernfs_node_dentry(cgrp->kn, sb);
2132 		dput(fc->root);
2133 		fc->root = nsdentry;
2134 		if (IS_ERR(nsdentry)) {
2135 			ret = PTR_ERR(nsdentry);
2136 			deactivate_locked_super(sb);
2137 		}
2138 	}
2139 
2140 	if (!ctx->kfc.new_sb_created)
2141 		cgroup_put(&ctx->root->cgrp);
2142 
2143 	return ret;
2144 }
2145 
2146 /*
2147  * Destroy a cgroup filesystem context.
2148  */
2149 static void cgroup_fs_context_free(struct fs_context *fc)
2150 {
2151 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2152 
2153 	kfree(ctx->name);
2154 	kfree(ctx->release_agent);
2155 	put_cgroup_ns(ctx->ns);
2156 	kernfs_free_fs_context(fc);
2157 	kfree(ctx);
2158 }
2159 
2160 static int cgroup_get_tree(struct fs_context *fc)
2161 {
2162 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2163 	int ret;
2164 
2165 	cgrp_dfl_visible = true;
2166 	cgroup_get_live(&cgrp_dfl_root.cgrp);
2167 	ctx->root = &cgrp_dfl_root;
2168 
2169 	ret = cgroup_do_get_tree(fc);
2170 	if (!ret)
2171 		apply_cgroup_root_flags(ctx->flags);
2172 	return ret;
2173 }
2174 
2175 static const struct fs_context_operations cgroup_fs_context_ops = {
2176 	.free		= cgroup_fs_context_free,
2177 	.parse_param	= cgroup2_parse_param,
2178 	.get_tree	= cgroup_get_tree,
2179 	.reconfigure	= cgroup_reconfigure,
2180 };
2181 
2182 static const struct fs_context_operations cgroup1_fs_context_ops = {
2183 	.free		= cgroup_fs_context_free,
2184 	.parse_param	= cgroup1_parse_param,
2185 	.get_tree	= cgroup1_get_tree,
2186 	.reconfigure	= cgroup1_reconfigure,
2187 };
2188 
2189 /*
2190  * Initialise the cgroup filesystem creation/reconfiguration context.  Notably,
2191  * we select the namespace we're going to use.
2192  */
2193 static int cgroup_init_fs_context(struct fs_context *fc)
2194 {
2195 	struct cgroup_fs_context *ctx;
2196 
2197 	ctx = kzalloc(sizeof(struct cgroup_fs_context), GFP_KERNEL);
2198 	if (!ctx)
2199 		return -ENOMEM;
2200 
2201 	/*
2202 	 * The first time anyone tries to mount a cgroup, enable the list
2203 	 * linking each css_set to its tasks and fix up all existing tasks.
2204 	 */
2205 	if (!use_task_css_set_links)
2206 		cgroup_enable_task_cg_lists();
2207 
2208 	ctx->ns = current->nsproxy->cgroup_ns;
2209 	get_cgroup_ns(ctx->ns);
2210 	fc->fs_private = &ctx->kfc;
2211 	if (fc->fs_type == &cgroup2_fs_type)
2212 		fc->ops = &cgroup_fs_context_ops;
2213 	else
2214 		fc->ops = &cgroup1_fs_context_ops;
2215 	if (fc->user_ns)
2216 		put_user_ns(fc->user_ns);
2217 	fc->user_ns = get_user_ns(ctx->ns->user_ns);
2218 	fc->global = true;
2219 	return 0;
2220 }
2221 
2222 static void cgroup_kill_sb(struct super_block *sb)
2223 {
2224 	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2225 	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2226 
2227 	/*
2228 	 * If @root doesn't have any children, start killing it.
2229 	 * This prevents new mounts by disabling percpu_ref_tryget_live().
2230 	 * cgroup_mount() may wait for @root's release.
2231 	 *
2232 	 * And don't kill the default root.
2233 	 */
2234 	if (list_empty(&root->cgrp.self.children) && root != &cgrp_dfl_root &&
2235 	    !percpu_ref_is_dying(&root->cgrp.self.refcnt))
2236 		percpu_ref_kill(&root->cgrp.self.refcnt);
2237 	cgroup_put(&root->cgrp);
2238 	kernfs_kill_sb(sb);
2239 }
2240 
2241 struct file_system_type cgroup_fs_type = {
2242 	.name			= "cgroup",
2243 	.init_fs_context	= cgroup_init_fs_context,
2244 	.parameters		= &cgroup1_fs_parameters,
2245 	.kill_sb		= cgroup_kill_sb,
2246 	.fs_flags		= FS_USERNS_MOUNT,
2247 };
2248 
2249 static struct file_system_type cgroup2_fs_type = {
2250 	.name			= "cgroup2",
2251 	.init_fs_context	= cgroup_init_fs_context,
2252 	.parameters		= &cgroup2_fs_parameters,
2253 	.kill_sb		= cgroup_kill_sb,
2254 	.fs_flags		= FS_USERNS_MOUNT,
2255 };
2256 
2257 int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2258 			  struct cgroup_namespace *ns)
2259 {
2260 	struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
2261 
2262 	return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
2263 }
2264 
2265 int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2266 		   struct cgroup_namespace *ns)
2267 {
2268 	int ret;
2269 
2270 	mutex_lock(&cgroup_mutex);
2271 	spin_lock_irq(&css_set_lock);
2272 
2273 	ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2274 
2275 	spin_unlock_irq(&css_set_lock);
2276 	mutex_unlock(&cgroup_mutex);
2277 
2278 	return ret;
2279 }
2280 EXPORT_SYMBOL_GPL(cgroup_path_ns);
2281 
2282 /**
2283  * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2284  * @task: target task
2285  * @buf: the buffer to write the path into
2286  * @buflen: the length of the buffer
2287  *
2288  * Determine @task's cgroup on the first (the one with the lowest non-zero
2289  * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2290  * function grabs cgroup_mutex and shouldn't be used inside locks used by
2291  * cgroup controller callbacks.
2292  *
2293  * Return value is the same as kernfs_path().
2294  */
2295 int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2296 {
2297 	struct cgroup_root *root;
2298 	struct cgroup *cgrp;
2299 	int hierarchy_id = 1;
2300 	int ret;
2301 
2302 	mutex_lock(&cgroup_mutex);
2303 	spin_lock_irq(&css_set_lock);
2304 
2305 	root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2306 
2307 	if (root) {
2308 		cgrp = task_cgroup_from_root(task, root);
2309 		ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2310 	} else {
2311 		/* if no hierarchy exists, everyone is in "/" */
2312 		ret = strlcpy(buf, "/", buflen);
2313 	}
2314 
2315 	spin_unlock_irq(&css_set_lock);
2316 	mutex_unlock(&cgroup_mutex);
2317 	return ret;
2318 }
2319 EXPORT_SYMBOL_GPL(task_cgroup_path);
2320 
2321 /**
2322  * cgroup_migrate_add_task - add a migration target task to a migration context
2323  * @task: target task
2324  * @mgctx: target migration context
2325  *
2326  * Add @task, which is a migration target, to @mgctx->tset.  This function
2327  * becomes noop if @task doesn't need to be migrated.  @task's css_set
2328  * should have been added as a migration source and @task->cg_list will be
2329  * moved from the css_set's tasks list to mg_tasks one.
2330  */
2331 static void cgroup_migrate_add_task(struct task_struct *task,
2332 				    struct cgroup_mgctx *mgctx)
2333 {
2334 	struct css_set *cset;
2335 
2336 	lockdep_assert_held(&css_set_lock);
2337 
2338 	/* @task either already exited or can't exit until the end */
2339 	if (task->flags & PF_EXITING)
2340 		return;
2341 
2342 	/* leave @task alone if post_fork() hasn't linked it yet */
2343 	if (list_empty(&task->cg_list))
2344 		return;
2345 
2346 	cset = task_css_set(task);
2347 	if (!cset->mg_src_cgrp)
2348 		return;
2349 
2350 	mgctx->tset.nr_tasks++;
2351 
2352 	list_move_tail(&task->cg_list, &cset->mg_tasks);
2353 	if (list_empty(&cset->mg_node))
2354 		list_add_tail(&cset->mg_node,
2355 			      &mgctx->tset.src_csets);
2356 	if (list_empty(&cset->mg_dst_cset->mg_node))
2357 		list_add_tail(&cset->mg_dst_cset->mg_node,
2358 			      &mgctx->tset.dst_csets);
2359 }
2360 
2361 /**
2362  * cgroup_taskset_first - reset taskset and return the first task
2363  * @tset: taskset of interest
2364  * @dst_cssp: output variable for the destination css
2365  *
2366  * @tset iteration is initialized and the first task is returned.
2367  */
2368 struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2369 					 struct cgroup_subsys_state **dst_cssp)
2370 {
2371 	tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2372 	tset->cur_task = NULL;
2373 
2374 	return cgroup_taskset_next(tset, dst_cssp);
2375 }
2376 
2377 /**
2378  * cgroup_taskset_next - iterate to the next task in taskset
2379  * @tset: taskset of interest
2380  * @dst_cssp: output variable for the destination css
2381  *
2382  * Return the next task in @tset.  Iteration must have been initialized
2383  * with cgroup_taskset_first().
2384  */
2385 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2386 					struct cgroup_subsys_state **dst_cssp)
2387 {
2388 	struct css_set *cset = tset->cur_cset;
2389 	struct task_struct *task = tset->cur_task;
2390 
2391 	while (&cset->mg_node != tset->csets) {
2392 		if (!task)
2393 			task = list_first_entry(&cset->mg_tasks,
2394 						struct task_struct, cg_list);
2395 		else
2396 			task = list_next_entry(task, cg_list);
2397 
2398 		if (&task->cg_list != &cset->mg_tasks) {
2399 			tset->cur_cset = cset;
2400 			tset->cur_task = task;
2401 
2402 			/*
2403 			 * This function may be called both before and
2404 			 * after cgroup_taskset_migrate().  The two cases
2405 			 * can be distinguished by looking at whether @cset
2406 			 * has its ->mg_dst_cset set.
2407 			 */
2408 			if (cset->mg_dst_cset)
2409 				*dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2410 			else
2411 				*dst_cssp = cset->subsys[tset->ssid];
2412 
2413 			return task;
2414 		}
2415 
2416 		cset = list_next_entry(cset, mg_node);
2417 		task = NULL;
2418 	}
2419 
2420 	return NULL;
2421 }
2422 
2423 /**
2424  * cgroup_taskset_migrate - migrate a taskset
2425  * @mgctx: migration context
2426  *
2427  * Migrate tasks in @mgctx as setup by migration preparation functions.
2428  * This function fails iff one of the ->can_attach callbacks fails and
2429  * guarantees that either all or none of the tasks in @mgctx are migrated.
2430  * @mgctx is consumed regardless of success.
2431  */
2432 static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
2433 {
2434 	struct cgroup_taskset *tset = &mgctx->tset;
2435 	struct cgroup_subsys *ss;
2436 	struct task_struct *task, *tmp_task;
2437 	struct css_set *cset, *tmp_cset;
2438 	int ssid, failed_ssid, ret;
2439 
2440 	/* check that we can legitimately attach to the cgroup */
2441 	if (tset->nr_tasks) {
2442 		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2443 			if (ss->can_attach) {
2444 				tset->ssid = ssid;
2445 				ret = ss->can_attach(tset);
2446 				if (ret) {
2447 					failed_ssid = ssid;
2448 					goto out_cancel_attach;
2449 				}
2450 			}
2451 		} while_each_subsys_mask();
2452 	}
2453 
2454 	/*
2455 	 * Now that we're guaranteed success, proceed to move all tasks to
2456 	 * the new cgroup.  There are no failure cases after here, so this
2457 	 * is the commit point.
2458 	 */
2459 	spin_lock_irq(&css_set_lock);
2460 	list_for_each_entry(cset, &tset->src_csets, mg_node) {
2461 		list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2462 			struct css_set *from_cset = task_css_set(task);
2463 			struct css_set *to_cset = cset->mg_dst_cset;
2464 
2465 			get_css_set(to_cset);
2466 			to_cset->nr_tasks++;
2467 			css_set_move_task(task, from_cset, to_cset, true);
2468 			from_cset->nr_tasks--;
2469 			/*
2470 			 * If the source or destination cgroup is frozen,
2471 			 * the task might require to change its state.
2472 			 */
2473 			cgroup_freezer_migrate_task(task, from_cset->dfl_cgrp,
2474 						    to_cset->dfl_cgrp);
2475 			put_css_set_locked(from_cset);
2476 
2477 		}
2478 	}
2479 	spin_unlock_irq(&css_set_lock);
2480 
2481 	/*
2482 	 * Migration is committed, all target tasks are now on dst_csets.
2483 	 * Nothing is sensitive to fork() after this point.  Notify
2484 	 * controllers that migration is complete.
2485 	 */
2486 	tset->csets = &tset->dst_csets;
2487 
2488 	if (tset->nr_tasks) {
2489 		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2490 			if (ss->attach) {
2491 				tset->ssid = ssid;
2492 				ss->attach(tset);
2493 			}
2494 		} while_each_subsys_mask();
2495 	}
2496 
2497 	ret = 0;
2498 	goto out_release_tset;
2499 
2500 out_cancel_attach:
2501 	if (tset->nr_tasks) {
2502 		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2503 			if (ssid == failed_ssid)
2504 				break;
2505 			if (ss->cancel_attach) {
2506 				tset->ssid = ssid;
2507 				ss->cancel_attach(tset);
2508 			}
2509 		} while_each_subsys_mask();
2510 	}
2511 out_release_tset:
2512 	spin_lock_irq(&css_set_lock);
2513 	list_splice_init(&tset->dst_csets, &tset->src_csets);
2514 	list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2515 		list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2516 		list_del_init(&cset->mg_node);
2517 	}
2518 	spin_unlock_irq(&css_set_lock);
2519 
2520 	/*
2521 	 * Re-initialize the cgroup_taskset structure in case it is reused
2522 	 * again in another cgroup_migrate_add_task()/cgroup_migrate_execute()
2523 	 * iteration.
2524 	 */
2525 	tset->nr_tasks = 0;
2526 	tset->csets    = &tset->src_csets;
2527 	return ret;
2528 }
2529 
2530 /**
2531  * cgroup_migrate_vet_dst - verify whether a cgroup can be migration destination
2532  * @dst_cgrp: destination cgroup to test
2533  *
2534  * On the default hierarchy, except for the mixable, (possible) thread root
2535  * and threaded cgroups, subtree_control must be zero for migration
2536  * destination cgroups with tasks so that child cgroups don't compete
2537  * against tasks.
2538  */
2539 int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp)
2540 {
2541 	/* v1 doesn't have any restriction */
2542 	if (!cgroup_on_dfl(dst_cgrp))
2543 		return 0;
2544 
2545 	/* verify @dst_cgrp can host resources */
2546 	if (!cgroup_is_valid_domain(dst_cgrp->dom_cgrp))
2547 		return -EOPNOTSUPP;
2548 
2549 	/* mixables don't care */
2550 	if (cgroup_is_mixable(dst_cgrp))
2551 		return 0;
2552 
2553 	/*
2554 	 * If @dst_cgrp is already or can become a thread root or is
2555 	 * threaded, it doesn't matter.
2556 	 */
2557 	if (cgroup_can_be_thread_root(dst_cgrp) || cgroup_is_threaded(dst_cgrp))
2558 		return 0;
2559 
2560 	/* apply no-internal-process constraint */
2561 	if (dst_cgrp->subtree_control)
2562 		return -EBUSY;
2563 
2564 	return 0;
2565 }
2566 
2567 /**
2568  * cgroup_migrate_finish - cleanup after attach
2569  * @mgctx: migration context
2570  *
2571  * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2572  * those functions for details.
2573  */
2574 void cgroup_migrate_finish(struct cgroup_mgctx *mgctx)
2575 {
2576 	LIST_HEAD(preloaded);
2577 	struct css_set *cset, *tmp_cset;
2578 
2579 	lockdep_assert_held(&cgroup_mutex);
2580 
2581 	spin_lock_irq(&css_set_lock);
2582 
2583 	list_splice_tail_init(&mgctx->preloaded_src_csets, &preloaded);
2584 	list_splice_tail_init(&mgctx->preloaded_dst_csets, &preloaded);
2585 
2586 	list_for_each_entry_safe(cset, tmp_cset, &preloaded, mg_preload_node) {
2587 		cset->mg_src_cgrp = NULL;
2588 		cset->mg_dst_cgrp = NULL;
2589 		cset->mg_dst_cset = NULL;
2590 		list_del_init(&cset->mg_preload_node);
2591 		put_css_set_locked(cset);
2592 	}
2593 
2594 	spin_unlock_irq(&css_set_lock);
2595 }
2596 
2597 /**
2598  * cgroup_migrate_add_src - add a migration source css_set
2599  * @src_cset: the source css_set to add
2600  * @dst_cgrp: the destination cgroup
2601  * @mgctx: migration context
2602  *
2603  * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2604  * @src_cset and add it to @mgctx->src_csets, which should later be cleaned
2605  * up by cgroup_migrate_finish().
2606  *
2607  * This function may be called without holding cgroup_threadgroup_rwsem
2608  * even if the target is a process.  Threads may be created and destroyed
2609  * but as long as cgroup_mutex is not dropped, no new css_set can be put
2610  * into play and the preloaded css_sets are guaranteed to cover all
2611  * migrations.
2612  */
2613 void cgroup_migrate_add_src(struct css_set *src_cset,
2614 			    struct cgroup *dst_cgrp,
2615 			    struct cgroup_mgctx *mgctx)
2616 {
2617 	struct cgroup *src_cgrp;
2618 
2619 	lockdep_assert_held(&cgroup_mutex);
2620 	lockdep_assert_held(&css_set_lock);
2621 
2622 	/*
2623 	 * If ->dead, @src_set is associated with one or more dead cgroups
2624 	 * and doesn't contain any migratable tasks.  Ignore it early so
2625 	 * that the rest of migration path doesn't get confused by it.
2626 	 */
2627 	if (src_cset->dead)
2628 		return;
2629 
2630 	src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2631 
2632 	if (!list_empty(&src_cset->mg_preload_node))
2633 		return;
2634 
2635 	WARN_ON(src_cset->mg_src_cgrp);
2636 	WARN_ON(src_cset->mg_dst_cgrp);
2637 	WARN_ON(!list_empty(&src_cset->mg_tasks));
2638 	WARN_ON(!list_empty(&src_cset->mg_node));
2639 
2640 	src_cset->mg_src_cgrp = src_cgrp;
2641 	src_cset->mg_dst_cgrp = dst_cgrp;
2642 	get_css_set(src_cset);
2643 	list_add_tail(&src_cset->mg_preload_node, &mgctx->preloaded_src_csets);
2644 }
2645 
2646 /**
2647  * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2648  * @mgctx: migration context
2649  *
2650  * Tasks are about to be moved and all the source css_sets have been
2651  * preloaded to @mgctx->preloaded_src_csets.  This function looks up and
2652  * pins all destination css_sets, links each to its source, and append them
2653  * to @mgctx->preloaded_dst_csets.
2654  *
2655  * This function must be called after cgroup_migrate_add_src() has been
2656  * called on each migration source css_set.  After migration is performed
2657  * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2658  * @mgctx.
2659  */
2660 int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
2661 {
2662 	struct css_set *src_cset, *tmp_cset;
2663 
2664 	lockdep_assert_held(&cgroup_mutex);
2665 
2666 	/* look up the dst cset for each src cset and link it to src */
2667 	list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,
2668 				 mg_preload_node) {
2669 		struct css_set *dst_cset;
2670 		struct cgroup_subsys *ss;
2671 		int ssid;
2672 
2673 		dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2674 		if (!dst_cset)
2675 			return -ENOMEM;
2676 
2677 		WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2678 
2679 		/*
2680 		 * If src cset equals dst, it's noop.  Drop the src.
2681 		 * cgroup_migrate() will skip the cset too.  Note that we
2682 		 * can't handle src == dst as some nodes are used by both.
2683 		 */
2684 		if (src_cset == dst_cset) {
2685 			src_cset->mg_src_cgrp = NULL;
2686 			src_cset->mg_dst_cgrp = NULL;
2687 			list_del_init(&src_cset->mg_preload_node);
2688 			put_css_set(src_cset);
2689 			put_css_set(dst_cset);
2690 			continue;
2691 		}
2692 
2693 		src_cset->mg_dst_cset = dst_cset;
2694 
2695 		if (list_empty(&dst_cset->mg_preload_node))
2696 			list_add_tail(&dst_cset->mg_preload_node,
2697 				      &mgctx->preloaded_dst_csets);
2698 		else
2699 			put_css_set(dst_cset);
2700 
2701 		for_each_subsys(ss, ssid)
2702 			if (src_cset->subsys[ssid] != dst_cset->subsys[ssid])
2703 				mgctx->ss_mask |= 1 << ssid;
2704 	}
2705 
2706 	return 0;
2707 }
2708 
2709 /**
2710  * cgroup_migrate - migrate a process or task to a cgroup
2711  * @leader: the leader of the process or the task to migrate
2712  * @threadgroup: whether @leader points to the whole process or a single task
2713  * @mgctx: migration context
2714  *
2715  * Migrate a process or task denoted by @leader.  If migrating a process,
2716  * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2717  * responsible for invoking cgroup_migrate_add_src() and
2718  * cgroup_migrate_prepare_dst() on the targets before invoking this
2719  * function and following up with cgroup_migrate_finish().
2720  *
2721  * As long as a controller's ->can_attach() doesn't fail, this function is
2722  * guaranteed to succeed.  This means that, excluding ->can_attach()
2723  * failure, when migrating multiple targets, the success or failure can be
2724  * decided for all targets by invoking group_migrate_prepare_dst() before
2725  * actually starting migrating.
2726  */
2727 int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2728 		   struct cgroup_mgctx *mgctx)
2729 {
2730 	struct task_struct *task;
2731 
2732 	/*
2733 	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
2734 	 * already PF_EXITING could be freed from underneath us unless we
2735 	 * take an rcu_read_lock.
2736 	 */
2737 	spin_lock_irq(&css_set_lock);
2738 	rcu_read_lock();
2739 	task = leader;
2740 	do {
2741 		cgroup_migrate_add_task(task, mgctx);
2742 		if (!threadgroup)
2743 			break;
2744 	} while_each_thread(leader, task);
2745 	rcu_read_unlock();
2746 	spin_unlock_irq(&css_set_lock);
2747 
2748 	return cgroup_migrate_execute(mgctx);
2749 }
2750 
2751 /**
2752  * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2753  * @dst_cgrp: the cgroup to attach to
2754  * @leader: the task or the leader of the threadgroup to be attached
2755  * @threadgroup: attach the whole threadgroup?
2756  *
2757  * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2758  */
2759 int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
2760 		       bool threadgroup)
2761 {
2762 	DEFINE_CGROUP_MGCTX(mgctx);
2763 	struct task_struct *task;
2764 	int ret;
2765 
2766 	ret = cgroup_migrate_vet_dst(dst_cgrp);
2767 	if (ret)
2768 		return ret;
2769 
2770 	/* look up all src csets */
2771 	spin_lock_irq(&css_set_lock);
2772 	rcu_read_lock();
2773 	task = leader;
2774 	do {
2775 		cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
2776 		if (!threadgroup)
2777 			break;
2778 	} while_each_thread(leader, task);
2779 	rcu_read_unlock();
2780 	spin_unlock_irq(&css_set_lock);
2781 
2782 	/* prepare dst csets and commit */
2783 	ret = cgroup_migrate_prepare_dst(&mgctx);
2784 	if (!ret)
2785 		ret = cgroup_migrate(leader, threadgroup, &mgctx);
2786 
2787 	cgroup_migrate_finish(&mgctx);
2788 
2789 	if (!ret)
2790 		TRACE_CGROUP_PATH(attach_task, dst_cgrp, leader, threadgroup);
2791 
2792 	return ret;
2793 }
2794 
2795 struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
2796 	__acquires(&cgroup_threadgroup_rwsem)
2797 {
2798 	struct task_struct *tsk;
2799 	pid_t pid;
2800 
2801 	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2802 		return ERR_PTR(-EINVAL);
2803 
2804 	percpu_down_write(&cgroup_threadgroup_rwsem);
2805 
2806 	rcu_read_lock();
2807 	if (pid) {
2808 		tsk = find_task_by_vpid(pid);
2809 		if (!tsk) {
2810 			tsk = ERR_PTR(-ESRCH);
2811 			goto out_unlock_threadgroup;
2812 		}
2813 	} else {
2814 		tsk = current;
2815 	}
2816 
2817 	if (threadgroup)
2818 		tsk = tsk->group_leader;
2819 
2820 	/*
2821 	 * kthreads may acquire PF_NO_SETAFFINITY during initialization.
2822 	 * If userland migrates such a kthread to a non-root cgroup, it can
2823 	 * become trapped in a cpuset, or RT kthread may be born in a
2824 	 * cgroup with no rt_runtime allocated.  Just say no.
2825 	 */
2826 	if (tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) {
2827 		tsk = ERR_PTR(-EINVAL);
2828 		goto out_unlock_threadgroup;
2829 	}
2830 
2831 	get_task_struct(tsk);
2832 	goto out_unlock_rcu;
2833 
2834 out_unlock_threadgroup:
2835 	percpu_up_write(&cgroup_threadgroup_rwsem);
2836 out_unlock_rcu:
2837 	rcu_read_unlock();
2838 	return tsk;
2839 }
2840 
2841 void cgroup_procs_write_finish(struct task_struct *task)
2842 	__releases(&cgroup_threadgroup_rwsem)
2843 {
2844 	struct cgroup_subsys *ss;
2845 	int ssid;
2846 
2847 	/* release reference from cgroup_procs_write_start() */
2848 	put_task_struct(task);
2849 
2850 	percpu_up_write(&cgroup_threadgroup_rwsem);
2851 	for_each_subsys(ss, ssid)
2852 		if (ss->post_attach)
2853 			ss->post_attach();
2854 }
2855 
2856 static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
2857 {
2858 	struct cgroup_subsys *ss;
2859 	bool printed = false;
2860 	int ssid;
2861 
2862 	do_each_subsys_mask(ss, ssid, ss_mask) {
2863 		if (printed)
2864 			seq_putc(seq, ' ');
2865 		seq_printf(seq, "%s", ss->name);
2866 		printed = true;
2867 	} while_each_subsys_mask();
2868 	if (printed)
2869 		seq_putc(seq, '\n');
2870 }
2871 
2872 /* show controllers which are enabled from the parent */
2873 static int cgroup_controllers_show(struct seq_file *seq, void *v)
2874 {
2875 	struct cgroup *cgrp = seq_css(seq)->cgroup;
2876 
2877 	cgroup_print_ss_mask(seq, cgroup_control(cgrp));
2878 	return 0;
2879 }
2880 
2881 /* show controllers which are enabled for a given cgroup's children */
2882 static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
2883 {
2884 	struct cgroup *cgrp = seq_css(seq)->cgroup;
2885 
2886 	cgroup_print_ss_mask(seq, cgrp->subtree_control);
2887 	return 0;
2888 }
2889 
2890 /**
2891  * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
2892  * @cgrp: root of the subtree to update csses for
2893  *
2894  * @cgrp's control masks have changed and its subtree's css associations
2895  * need to be updated accordingly.  This function looks up all css_sets
2896  * which are attached to the subtree, creates the matching updated css_sets
2897  * and migrates the tasks to the new ones.
2898  */
2899 static int cgroup_update_dfl_csses(struct cgroup *cgrp)
2900 {
2901 	DEFINE_CGROUP_MGCTX(mgctx);
2902 	struct cgroup_subsys_state *d_css;
2903 	struct cgroup *dsct;
2904 	struct css_set *src_cset;
2905 	int ret;
2906 
2907 	lockdep_assert_held(&cgroup_mutex);
2908 
2909 	percpu_down_write(&cgroup_threadgroup_rwsem);
2910 
2911 	/* look up all csses currently attached to @cgrp's subtree */
2912 	spin_lock_irq(&css_set_lock);
2913 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2914 		struct cgrp_cset_link *link;
2915 
2916 		list_for_each_entry(link, &dsct->cset_links, cset_link)
2917 			cgroup_migrate_add_src(link->cset, dsct, &mgctx);
2918 	}
2919 	spin_unlock_irq(&css_set_lock);
2920 
2921 	/* NULL dst indicates self on default hierarchy */
2922 	ret = cgroup_migrate_prepare_dst(&mgctx);
2923 	if (ret)
2924 		goto out_finish;
2925 
2926 	spin_lock_irq(&css_set_lock);
2927 	list_for_each_entry(src_cset, &mgctx.preloaded_src_csets, mg_preload_node) {
2928 		struct task_struct *task, *ntask;
2929 
2930 		/* all tasks in src_csets need to be migrated */
2931 		list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
2932 			cgroup_migrate_add_task(task, &mgctx);
2933 	}
2934 	spin_unlock_irq(&css_set_lock);
2935 
2936 	ret = cgroup_migrate_execute(&mgctx);
2937 out_finish:
2938 	cgroup_migrate_finish(&mgctx);
2939 	percpu_up_write(&cgroup_threadgroup_rwsem);
2940 	return ret;
2941 }
2942 
2943 /**
2944  * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
2945  * @cgrp: root of the target subtree
2946  *
2947  * Because css offlining is asynchronous, userland may try to re-enable a
2948  * controller while the previous css is still around.  This function grabs
2949  * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
2950  */
2951 void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
2952 	__acquires(&cgroup_mutex)
2953 {
2954 	struct cgroup *dsct;
2955 	struct cgroup_subsys_state *d_css;
2956 	struct cgroup_subsys *ss;
2957 	int ssid;
2958 
2959 restart:
2960 	mutex_lock(&cgroup_mutex);
2961 
2962 	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
2963 		for_each_subsys(ss, ssid) {
2964 			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
2965 			DEFINE_WAIT(wait);
2966 
2967 			if (!css || !percpu_ref_is_dying(&css->refcnt))
2968 				continue;
2969 
2970 			cgroup_get_live(dsct);
2971 			prepare_to_wait(&dsct->offline_waitq, &wait,
2972 					TASK_UNINTERRUPTIBLE);
2973 
2974 			mutex_unlock(&cgroup_mutex);
2975 			schedule();
2976 			finish_wait(&dsct->offline_waitq, &wait);
2977 
2978 			cgroup_put(dsct);
2979 			goto restart;
2980 		}
2981 	}
2982 }
2983 
2984 /**
2985  * cgroup_save_control - save control masks and dom_cgrp of a subtree
2986  * @cgrp: root of the target subtree
2987  *
2988  * Save ->subtree_control, ->subtree_ss_mask and ->dom_cgrp to the
2989  * respective old_ prefixed fields for @cgrp's subtree including @cgrp
2990  * itself.
2991  */
2992 static void cgroup_save_control(struct cgroup *cgrp)
2993 {
2994 	struct cgroup *dsct;
2995 	struct cgroup_subsys_state *d_css;
2996 
2997 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2998 		dsct->old_subtree_control = dsct->subtree_control;
2999 		dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
3000 		dsct->old_dom_cgrp = dsct->dom_cgrp;
3001 	}
3002 }
3003 
3004 /**
3005  * cgroup_propagate_control - refresh control masks of a subtree
3006  * @cgrp: root of the target subtree
3007  *
3008  * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
3009  * ->subtree_control and propagate controller availability through the
3010  * subtree so that descendants don't have unavailable controllers enabled.
3011  */
3012 static void cgroup_propagate_control(struct cgroup *cgrp)
3013 {
3014 	struct cgroup *dsct;
3015 	struct cgroup_subsys_state *d_css;
3016 
3017 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3018 		dsct->subtree_control &= cgroup_control(dsct);
3019 		dsct->subtree_ss_mask =
3020 			cgroup_calc_subtree_ss_mask(dsct->subtree_control,
3021 						    cgroup_ss_mask(dsct));
3022 	}
3023 }
3024 
3025 /**
3026  * cgroup_restore_control - restore control masks and dom_cgrp of a subtree
3027  * @cgrp: root of the target subtree
3028  *
3029  * Restore ->subtree_control, ->subtree_ss_mask and ->dom_cgrp from the
3030  * respective old_ prefixed fields for @cgrp's subtree including @cgrp
3031  * itself.
3032  */
3033 static void cgroup_restore_control(struct cgroup *cgrp)
3034 {
3035 	struct cgroup *dsct;
3036 	struct cgroup_subsys_state *d_css;
3037 
3038 	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3039 		dsct->subtree_control = dsct->old_subtree_control;
3040 		dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
3041 		dsct->dom_cgrp = dsct->old_dom_cgrp;
3042 	}
3043 }
3044 
3045 static bool css_visible(struct cgroup_subsys_state *css)
3046 {
3047 	struct cgroup_subsys *ss = css->ss;
3048 	struct cgroup *cgrp = css->cgroup;
3049 
3050 	if (cgroup_control(cgrp) & (1 << ss->id))
3051 		return true;
3052 	if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
3053 		return false;
3054 	return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
3055 }
3056 
3057 /**
3058  * cgroup_apply_control_enable - enable or show csses according to control
3059  * @cgrp: root of the target subtree
3060  *
3061  * Walk @cgrp's subtree and create new csses or make the existing ones
3062  * visible.  A css is created invisible if it's being implicitly enabled
3063  * through dependency.  An invisible css is made visible when the userland
3064  * explicitly enables it.
3065  *
3066  * Returns 0 on success, -errno on failure.  On failure, csses which have
3067  * been processed already aren't cleaned up.  The caller is responsible for
3068  * cleaning up with cgroup_apply_control_disable().
3069  */
3070 static int cgroup_apply_control_enable(struct cgroup *cgrp)
3071 {
3072 	struct cgroup *dsct;
3073 	struct cgroup_subsys_state *d_css;
3074 	struct cgroup_subsys *ss;
3075 	int ssid, ret;
3076 
3077 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3078 		for_each_subsys(ss, ssid) {
3079 			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3080 
3081 			WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3082 
3083 			if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
3084 				continue;
3085 
3086 			if (!css) {
3087 				css = css_create(dsct, ss);
3088 				if (IS_ERR(css))
3089 					return PTR_ERR(css);
3090 			}
3091 
3092 			if (css_visible(css)) {
3093 				ret = css_populate_dir(css);
3094 				if (ret)
3095 					return ret;
3096 			}
3097 		}
3098 	}
3099 
3100 	return 0;
3101 }
3102 
3103 /**
3104  * cgroup_apply_control_disable - kill or hide csses according to control
3105  * @cgrp: root of the target subtree
3106  *
3107  * Walk @cgrp's subtree and kill and hide csses so that they match
3108  * cgroup_ss_mask() and cgroup_visible_mask().
3109  *
3110  * A css is hidden when the userland requests it to be disabled while other
3111  * subsystems are still depending on it.  The css must not actively control
3112  * resources and be in the vanilla state if it's made visible again later.
3113  * Controllers which may be depended upon should provide ->css_reset() for
3114  * this purpose.
3115  */
3116 static void cgroup_apply_control_disable(struct cgroup *cgrp)
3117 {
3118 	struct cgroup *dsct;
3119 	struct cgroup_subsys_state *d_css;
3120 	struct cgroup_subsys *ss;
3121 	int ssid;
3122 
3123 	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3124 		for_each_subsys(ss, ssid) {
3125 			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3126 
3127 			WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3128 
3129 			if (!css)
3130 				continue;
3131 
3132 			if (css->parent &&
3133 			    !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
3134 				kill_css(css);
3135 			} else if (!css_visible(css)) {
3136 				css_clear_dir(css);
3137 				if (ss->css_reset)
3138 					ss->css_reset(css);
3139 			}
3140 		}
3141 	}
3142 }
3143 
3144 /**
3145  * cgroup_apply_control - apply control mask updates to the subtree
3146  * @cgrp: root of the target subtree
3147  *
3148  * subsystems can be enabled and disabled in a subtree using the following
3149  * steps.
3150  *
3151  * 1. Call cgroup_save_control() to stash the current state.
3152  * 2. Update ->subtree_control masks in the subtree as desired.
3153  * 3. Call cgroup_apply_control() to apply the changes.
3154  * 4. Optionally perform other related operations.
3155  * 5. Call cgroup_finalize_control() to finish up.
3156  *
3157  * This function implements step 3 and propagates the mask changes
3158  * throughout @cgrp's subtree, updates csses accordingly and perform
3159  * process migrations.
3160  */
3161 static int cgroup_apply_control(struct cgroup *cgrp)
3162 {
3163 	int ret;
3164 
3165 	cgroup_propagate_control(cgrp);
3166 
3167 	ret = cgroup_apply_control_enable(cgrp);
3168 	if (ret)
3169 		return ret;
3170 
3171 	/*
3172 	 * At this point, cgroup_e_css_by_mask() results reflect the new csses
3173 	 * making the following cgroup_update_dfl_csses() properly update
3174 	 * css associations of all tasks in the subtree.
3175 	 */
3176 	ret = cgroup_update_dfl_csses(cgrp);
3177 	if (ret)
3178 		return ret;
3179 
3180 	return 0;
3181 }
3182 
3183 /**
3184  * cgroup_finalize_control - finalize control mask update
3185  * @cgrp: root of the target subtree
3186  * @ret: the result of the update
3187  *
3188  * Finalize control mask update.  See cgroup_apply_control() for more info.
3189  */
3190 static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3191 {
3192 	if (ret) {
3193 		cgroup_restore_control(cgrp);
3194 		cgroup_propagate_control(cgrp);
3195 	}
3196 
3197 	cgroup_apply_control_disable(cgrp);
3198 }
3199 
3200 static int cgroup_vet_subtree_control_enable(struct cgroup *cgrp, u16 enable)
3201 {
3202 	u16 domain_enable = enable & ~cgrp_dfl_threaded_ss_mask;
3203 
3204 	/* if nothing is getting enabled, nothing to worry about */
3205 	if (!enable)
3206 		return 0;
3207 
3208 	/* can @cgrp host any resources? */
3209 	if (!cgroup_is_valid_domain(cgrp->dom_cgrp))
3210 		return -EOPNOTSUPP;
3211 
3212 	/* mixables don't care */
3213 	if (cgroup_is_mixable(cgrp))
3214 		return 0;
3215 
3216 	if (domain_enable) {
3217 		/* can't enable domain controllers inside a thread subtree */
3218 		if (cgroup_is_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3219 			return -EOPNOTSUPP;
3220 	} else {
3221 		/*
3222 		 * Threaded controllers can handle internal competitions
3223 		 * and are always allowed inside a (prospective) thread
3224 		 * subtree.
3225 		 */
3226 		if (cgroup_can_be_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3227 			return 0;
3228 	}
3229 
3230 	/*
3231 	 * Controllers can't be enabled for a cgroup with tasks to avoid
3232 	 * child cgroups competing against tasks.
3233 	 */
3234 	if (cgroup_has_tasks(cgrp))
3235 		return -EBUSY;
3236 
3237 	return 0;
3238 }
3239 
3240 /* change the enabled child controllers for a cgroup in the default hierarchy */
3241 static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3242 					    char *buf, size_t nbytes,
3243 					    loff_t off)
3244 {
3245 	u16 enable = 0, disable = 0;
3246 	struct cgroup *cgrp, *child;
3247 	struct cgroup_subsys *ss;
3248 	char *tok;
3249 	int ssid, ret;
3250 
3251 	/*
3252 	 * Parse input - space separated list of subsystem names prefixed
3253 	 * with either + or -.
3254 	 */
3255 	buf = strstrip(buf);
3256 	while ((tok = strsep(&buf, " "))) {
3257 		if (tok[0] == '\0')
3258 			continue;
3259 		do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3260 			if (!cgroup_ssid_enabled(ssid) ||
3261 			    strcmp(tok + 1, ss->name))
3262 				continue;
3263 
3264 			if (*tok == '+') {
3265 				enable |= 1 << ssid;
3266 				disable &= ~(1 << ssid);
3267 			} else if (*tok == '-') {
3268 				disable |= 1 << ssid;
3269 				enable &= ~(1 << ssid);
3270 			} else {
3271 				return -EINVAL;
3272 			}
3273 			break;
3274 		} while_each_subsys_mask();
3275 		if (ssid == CGROUP_SUBSYS_COUNT)
3276 			return -EINVAL;
3277 	}
3278 
3279 	cgrp = cgroup_kn_lock_live(of->kn, true);
3280 	if (!cgrp)
3281 		return -ENODEV;
3282 
3283 	for_each_subsys(ss, ssid) {
3284 		if (enable & (1 << ssid)) {
3285 			if (cgrp->subtree_control & (1 << ssid)) {
3286 				enable &= ~(1 << ssid);
3287 				continue;
3288 			}
3289 
3290 			if (!(cgroup_control(cgrp) & (1 << ssid))) {
3291 				ret = -ENOENT;
3292 				goto out_unlock;
3293 			}
3294 		} else if (disable & (1 << ssid)) {
3295 			if (!(cgrp->subtree_control & (1 << ssid))) {
3296 				disable &= ~(1 << ssid);
3297 				continue;
3298 			}
3299 
3300 			/* a child has it enabled? */
3301 			cgroup_for_each_live_child(child, cgrp) {
3302 				if (child->subtree_control & (1 << ssid)) {
3303 					ret = -EBUSY;
3304 					goto out_unlock;
3305 				}
3306 			}
3307 		}
3308 	}
3309 
3310 	if (!enable && !disable) {
3311 		ret = 0;
3312 		goto out_unlock;
3313 	}
3314 
3315 	ret = cgroup_vet_subtree_control_enable(cgrp, enable);
3316 	if (ret)
3317 		goto out_unlock;
3318 
3319 	/* save and update control masks and prepare csses */
3320 	cgroup_save_control(cgrp);
3321 
3322 	cgrp->subtree_control |= enable;
3323 	cgrp->subtree_control &= ~disable;
3324 
3325 	ret = cgroup_apply_control(cgrp);
3326 	cgroup_finalize_control(cgrp, ret);
3327 	if (ret)
3328 		goto out_unlock;
3329 
3330 	kernfs_activate(cgrp->kn);
3331 out_unlock:
3332 	cgroup_kn_unlock(of->kn);
3333 	return ret ?: nbytes;
3334 }
3335 
3336 /**
3337  * cgroup_enable_threaded - make @cgrp threaded
3338  * @cgrp: the target cgroup
3339  *
3340  * Called when "threaded" is written to the cgroup.type interface file and
3341  * tries to make @cgrp threaded and join the parent's resource domain.
3342  * This function is never called on the root cgroup as cgroup.type doesn't
3343  * exist on it.
3344  */
3345 static int cgroup_enable_threaded(struct cgroup *cgrp)
3346 {
3347 	struct cgroup *parent = cgroup_parent(cgrp);
3348 	struct cgroup *dom_cgrp = parent->dom_cgrp;
3349 	struct cgroup *dsct;
3350 	struct cgroup_subsys_state *d_css;
3351 	int ret;
3352 
3353 	lockdep_assert_held(&cgroup_mutex);
3354 
3355 	/* noop if already threaded */
3356 	if (cgroup_is_threaded(cgrp))
3357 		return 0;
3358 
3359 	/*
3360 	 * If @cgroup is populated or has domain controllers enabled, it
3361 	 * can't be switched.  While the below cgroup_can_be_thread_root()
3362 	 * test can catch the same conditions, that's only when @parent is
3363 	 * not mixable, so let's check it explicitly.
3364 	 */
3365 	if (cgroup_is_populated(cgrp) ||
3366 	    cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
3367 		return -EOPNOTSUPP;
3368 
3369 	/* we're joining the parent's domain, ensure its validity */
3370 	if (!cgroup_is_valid_domain(dom_cgrp) ||
3371 	    !cgroup_can_be_thread_root(dom_cgrp))
3372 		return -EOPNOTSUPP;
3373 
3374 	/*
3375 	 * The following shouldn't cause actual migrations and should
3376 	 * always succeed.
3377 	 */
3378 	cgroup_save_control(cgrp);
3379 
3380 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)
3381 		if (dsct == cgrp || cgroup_is_threaded(dsct))
3382 			dsct->dom_cgrp = dom_cgrp;
3383 
3384 	ret = cgroup_apply_control(cgrp);
3385 	if (!ret)
3386 		parent->nr_threaded_children++;
3387 
3388 	cgroup_finalize_control(cgrp, ret);
3389 	return ret;
3390 }
3391 
3392 static int cgroup_type_show(struct seq_file *seq, void *v)
3393 {
3394 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3395 
3396 	if (cgroup_is_threaded(cgrp))
3397 		seq_puts(seq, "threaded\n");
3398 	else if (!cgroup_is_valid_domain(cgrp))
3399 		seq_puts(seq, "domain invalid\n");
3400 	else if (cgroup_is_thread_root(cgrp))
3401 		seq_puts(seq, "domain threaded\n");
3402 	else
3403 		seq_puts(seq, "domain\n");
3404 
3405 	return 0;
3406 }
3407 
3408 static ssize_t cgroup_type_write(struct kernfs_open_file *of, char *buf,
3409 				 size_t nbytes, loff_t off)
3410 {
3411 	struct cgroup *cgrp;
3412 	int ret;
3413 
3414 	/* only switching to threaded mode is supported */
3415 	if (strcmp(strstrip(buf), "threaded"))
3416 		return -EINVAL;
3417 
3418 	cgrp = cgroup_kn_lock_live(of->kn, false);
3419 	if (!cgrp)
3420 		return -ENOENT;
3421 
3422 	/* threaded can only be enabled */
3423 	ret = cgroup_enable_threaded(cgrp);
3424 
3425 	cgroup_kn_unlock(of->kn);
3426 	return ret ?: nbytes;
3427 }
3428 
3429 static int cgroup_max_descendants_show(struct seq_file *seq, void *v)
3430 {
3431 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3432 	int descendants = READ_ONCE(cgrp->max_descendants);
3433 
3434 	if (descendants == INT_MAX)
3435 		seq_puts(seq, "max\n");
3436 	else
3437 		seq_printf(seq, "%d\n", descendants);
3438 
3439 	return 0;
3440 }
3441 
3442 static ssize_t cgroup_max_descendants_write(struct kernfs_open_file *of,
3443 					   char *buf, size_t nbytes, loff_t off)
3444 {
3445 	struct cgroup *cgrp;
3446 	int descendants;
3447 	ssize_t ret;
3448 
3449 	buf = strstrip(buf);
3450 	if (!strcmp(buf, "max")) {
3451 		descendants = INT_MAX;
3452 	} else {
3453 		ret = kstrtoint(buf, 0, &descendants);
3454 		if (ret)
3455 			return ret;
3456 	}
3457 
3458 	if (descendants < 0)
3459 		return -ERANGE;
3460 
3461 	cgrp = cgroup_kn_lock_live(of->kn, false);
3462 	if (!cgrp)
3463 		return -ENOENT;
3464 
3465 	cgrp->max_descendants = descendants;
3466 
3467 	cgroup_kn_unlock(of->kn);
3468 
3469 	return nbytes;
3470 }
3471 
3472 static int cgroup_max_depth_show(struct seq_file *seq, void *v)
3473 {
3474 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3475 	int depth = READ_ONCE(cgrp->max_depth);
3476 
3477 	if (depth == INT_MAX)
3478 		seq_puts(seq, "max\n");
3479 	else
3480 		seq_printf(seq, "%d\n", depth);
3481 
3482 	return 0;
3483 }
3484 
3485 static ssize_t cgroup_max_depth_write(struct kernfs_open_file *of,
3486 				      char *buf, size_t nbytes, loff_t off)
3487 {
3488 	struct cgroup *cgrp;
3489 	ssize_t ret;
3490 	int depth;
3491 
3492 	buf = strstrip(buf);
3493 	if (!strcmp(buf, "max")) {
3494 		depth = INT_MAX;
3495 	} else {
3496 		ret = kstrtoint(buf, 0, &depth);
3497 		if (ret)
3498 			return ret;
3499 	}
3500 
3501 	if (depth < 0)
3502 		return -ERANGE;
3503 
3504 	cgrp = cgroup_kn_lock_live(of->kn, false);
3505 	if (!cgrp)
3506 		return -ENOENT;
3507 
3508 	cgrp->max_depth = depth;
3509 
3510 	cgroup_kn_unlock(of->kn);
3511 
3512 	return nbytes;
3513 }
3514 
3515 static int cgroup_events_show(struct seq_file *seq, void *v)
3516 {
3517 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3518 
3519 	seq_printf(seq, "populated %d\n", cgroup_is_populated(cgrp));
3520 	seq_printf(seq, "frozen %d\n", test_bit(CGRP_FROZEN, &cgrp->flags));
3521 
3522 	return 0;
3523 }
3524 
3525 static int cgroup_stat_show(struct seq_file *seq, void *v)
3526 {
3527 	struct cgroup *cgroup = seq_css(seq)->cgroup;
3528 
3529 	seq_printf(seq, "nr_descendants %d\n",
3530 		   cgroup->nr_descendants);
3531 	seq_printf(seq, "nr_dying_descendants %d\n",
3532 		   cgroup->nr_dying_descendants);
3533 
3534 	return 0;
3535 }
3536 
3537 static int __maybe_unused cgroup_extra_stat_show(struct seq_file *seq,
3538 						 struct cgroup *cgrp, int ssid)
3539 {
3540 	struct cgroup_subsys *ss = cgroup_subsys[ssid];
3541 	struct cgroup_subsys_state *css;
3542 	int ret;
3543 
3544 	if (!ss->css_extra_stat_show)
3545 		return 0;
3546 
3547 	css = cgroup_tryget_css(cgrp, ss);
3548 	if (!css)
3549 		return 0;
3550 
3551 	ret = ss->css_extra_stat_show(seq, css);
3552 	css_put(css);
3553 	return ret;
3554 }
3555 
3556 static int cpu_stat_show(struct seq_file *seq, void *v)
3557 {
3558 	struct cgroup __maybe_unused *cgrp = seq_css(seq)->cgroup;
3559 	int ret = 0;
3560 
3561 	cgroup_base_stat_cputime_show(seq);
3562 #ifdef CONFIG_CGROUP_SCHED
3563 	ret = cgroup_extra_stat_show(seq, cgrp, cpu_cgrp_id);
3564 #endif
3565 	return ret;
3566 }
3567 
3568 #ifdef CONFIG_PSI
3569 static int cgroup_io_pressure_show(struct seq_file *seq, void *v)
3570 {
3571 	struct cgroup *cgroup = seq_css(seq)->cgroup;
3572 	struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
3573 
3574 	return psi_show(seq, psi, PSI_IO);
3575 }
3576 static int cgroup_memory_pressure_show(struct seq_file *seq, void *v)
3577 {
3578 	struct cgroup *cgroup = seq_css(seq)->cgroup;
3579 	struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
3580 
3581 	return psi_show(seq, psi, PSI_MEM);
3582 }
3583 static int cgroup_cpu_pressure_show(struct seq_file *seq, void *v)
3584 {
3585 	struct cgroup *cgroup = seq_css(seq)->cgroup;
3586 	struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
3587 
3588 	return psi_show(seq, psi, PSI_CPU);
3589 }
3590 
3591 static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf,
3592 					  size_t nbytes, enum psi_res res)
3593 {
3594 	struct psi_trigger *new;
3595 	struct cgroup *cgrp;
3596 
3597 	cgrp = cgroup_kn_lock_live(of->kn, false);
3598 	if (!cgrp)
3599 		return -ENODEV;
3600 
3601 	cgroup_get(cgrp);
3602 	cgroup_kn_unlock(of->kn);
3603 
3604 	new = psi_trigger_create(&cgrp->psi, buf, nbytes, res);
3605 	if (IS_ERR(new)) {
3606 		cgroup_put(cgrp);
3607 		return PTR_ERR(new);
3608 	}
3609 
3610 	psi_trigger_replace(&of->priv, new);
3611 
3612 	cgroup_put(cgrp);
3613 
3614 	return nbytes;
3615 }
3616 
3617 static ssize_t cgroup_io_pressure_write(struct kernfs_open_file *of,
3618 					  char *buf, size_t nbytes,
3619 					  loff_t off)
3620 {
3621 	return cgroup_pressure_write(of, buf, nbytes, PSI_IO);
3622 }
3623 
3624 static ssize_t cgroup_memory_pressure_write(struct kernfs_open_file *of,
3625 					  char *buf, size_t nbytes,
3626 					  loff_t off)
3627 {
3628 	return cgroup_pressure_write(of, buf, nbytes, PSI_MEM);
3629 }
3630 
3631 static ssize_t cgroup_cpu_pressure_write(struct kernfs_open_file *of,
3632 					  char *buf, size_t nbytes,
3633 					  loff_t off)
3634 {
3635 	return cgroup_pressure_write(of, buf, nbytes, PSI_CPU);
3636 }
3637 
3638 static __poll_t cgroup_pressure_poll(struct kernfs_open_file *of,
3639 					  poll_table *pt)
3640 {
3641 	return psi_trigger_poll(&of->priv, of->file, pt);
3642 }
3643 
3644 static void cgroup_pressure_release(struct kernfs_open_file *of)
3645 {
3646 	psi_trigger_replace(&of->priv, NULL);
3647 }
3648 #endif /* CONFIG_PSI */
3649 
3650 static int cgroup_freeze_show(struct seq_file *seq, void *v)
3651 {
3652 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3653 
3654 	seq_printf(seq, "%d\n", cgrp->freezer.freeze);
3655 
3656 	return 0;
3657 }
3658 
3659 static ssize_t cgroup_freeze_write(struct kernfs_open_file *of,
3660 				   char *buf, size_t nbytes, loff_t off)
3661 {
3662 	struct cgroup *cgrp;
3663 	ssize_t ret;
3664 	int freeze;
3665 
3666 	ret = kstrtoint(strstrip(buf), 0, &freeze);
3667 	if (ret)
3668 		return ret;
3669 
3670 	if (freeze < 0 || freeze > 1)
3671 		return -ERANGE;
3672 
3673 	cgrp = cgroup_kn_lock_live(of->kn, false);
3674 	if (!cgrp)
3675 		return -ENOENT;
3676 
3677 	cgroup_freeze(cgrp, freeze);
3678 
3679 	cgroup_kn_unlock(of->kn);
3680 
3681 	return nbytes;
3682 }
3683 
3684 static int cgroup_file_open(struct kernfs_open_file *of)
3685 {
3686 	struct cftype *cft = of->kn->priv;
3687 
3688 	if (cft->open)
3689 		return cft->open(of);
3690 	return 0;
3691 }
3692 
3693 static void cgroup_file_release(struct kernfs_open_file *of)
3694 {
3695 	struct cftype *cft = of->kn->priv;
3696 
3697 	if (cft->release)
3698 		cft->release(of);
3699 }
3700 
3701 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3702 				 size_t nbytes, loff_t off)
3703 {
3704 	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
3705 	struct cgroup *cgrp = of->kn->parent->priv;
3706 	struct cftype *cft = of->kn->priv;
3707 	struct cgroup_subsys_state *css;
3708 	int ret;
3709 
3710 	/*
3711 	 * If namespaces are delegation boundaries, disallow writes to
3712 	 * files in an non-init namespace root from inside the namespace
3713 	 * except for the files explicitly marked delegatable -
3714 	 * cgroup.procs and cgroup.subtree_control.
3715 	 */
3716 	if ((cgrp->root->flags & CGRP_ROOT_NS_DELEGATE) &&
3717 	    !(cft->flags & CFTYPE_NS_DELEGATABLE) &&
3718 	    ns != &init_cgroup_ns && ns->root_cset->dfl_cgrp == cgrp)
3719 		return -EPERM;
3720 
3721 	if (cft->write)
3722 		return cft->write(of, buf, nbytes, off);
3723 
3724 	/*
3725 	 * kernfs guarantees that a file isn't deleted with operations in
3726 	 * flight, which means that the matching css is and stays alive and
3727 	 * doesn't need to be pinned.  The RCU locking is not necessary
3728 	 * either.  It's just for the convenience of using cgroup_css().
3729 	 */
3730 	rcu_read_lock();
3731 	css = cgroup_css(cgrp, cft->ss);
3732 	rcu_read_unlock();
3733 
3734 	if (cft->write_u64) {
3735 		unsigned long long v;
3736 		ret = kstrtoull(buf, 0, &v);
3737 		if (!ret)
3738 			ret = cft->write_u64(css, cft, v);
3739 	} else if (cft->write_s64) {
3740 		long long v;
3741 		ret = kstrtoll(buf, 0, &v);
3742 		if (!ret)
3743 			ret = cft->write_s64(css, cft, v);
3744 	} else {
3745 		ret = -EINVAL;
3746 	}
3747 
3748 	return ret ?: nbytes;
3749 }
3750 
3751 static __poll_t cgroup_file_poll(struct kernfs_open_file *of, poll_table *pt)
3752 {
3753 	struct cftype *cft = of->kn->priv;
3754 
3755 	if (cft->poll)
3756 		return cft->poll(of, pt);
3757 
3758 	return kernfs_generic_poll(of, pt);
3759 }
3760 
3761 static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3762 {
3763 	return seq_cft(seq)->seq_start(seq, ppos);
3764 }
3765 
3766 static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3767 {
3768 	return seq_cft(seq)->seq_next(seq, v, ppos);
3769 }
3770 
3771 static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3772 {
3773 	if (seq_cft(seq)->seq_stop)
3774 		seq_cft(seq)->seq_stop(seq, v);
3775 }
3776 
3777 static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3778 {
3779 	struct cftype *cft = seq_cft(m);
3780 	struct cgroup_subsys_state *css = seq_css(m);
3781 
3782 	if (cft->seq_show)
3783 		return cft->seq_show(m, arg);
3784 
3785 	if (cft->read_u64)
3786 		seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3787 	else if (cft->read_s64)
3788 		seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3789 	else
3790 		return -EINVAL;
3791 	return 0;
3792 }
3793 
3794 static struct kernfs_ops cgroup_kf_single_ops = {
3795 	.atomic_write_len	= PAGE_SIZE,
3796 	.open			= cgroup_file_open,
3797 	.release		= cgroup_file_release,
3798 	.write			= cgroup_file_write,
3799 	.poll			= cgroup_file_poll,
3800 	.seq_show		= cgroup_seqfile_show,
3801 };
3802 
3803 static struct kernfs_ops cgroup_kf_ops = {
3804 	.atomic_write_len	= PAGE_SIZE,
3805 	.open			= cgroup_file_open,
3806 	.release		= cgroup_file_release,
3807 	.write			= cgroup_file_write,
3808 	.poll			= cgroup_file_poll,
3809 	.seq_start		= cgroup_seqfile_start,
3810 	.seq_next		= cgroup_seqfile_next,
3811 	.seq_stop		= cgroup_seqfile_stop,
3812 	.seq_show		= cgroup_seqfile_show,
3813 };
3814 
3815 /* set uid and gid of cgroup dirs and files to that of the creator */
3816 static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3817 {
3818 	struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3819 			       .ia_uid = current_fsuid(),
3820 			       .ia_gid = current_fsgid(), };
3821 
3822 	if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3823 	    gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3824 		return 0;
3825 
3826 	return kernfs_setattr(kn, &iattr);
3827 }
3828 
3829 static void cgroup_file_notify_timer(struct timer_list *timer)
3830 {
3831 	cgroup_file_notify(container_of(timer, struct cgroup_file,
3832 					notify_timer));
3833 }
3834 
3835 static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3836 			   struct cftype *cft)
3837 {
3838 	char name[CGROUP_FILE_NAME_MAX];
3839 	struct kernfs_node *kn;
3840 	struct kernfs_node *kn_link;
3841 	struct lock_class_key *key = NULL;
3842 	int ret;
3843 
3844 #ifdef CONFIG_DEBUG_LOCK_ALLOC
3845 	key = &cft->lockdep_key;
3846 #endif
3847 	kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3848 				  cgroup_file_mode(cft),
3849 				  GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
3850 				  0, cft->kf_ops, cft,
3851 				  NULL, key);
3852 	if (IS_ERR(kn))
3853 		return PTR_ERR(kn);
3854 
3855 	ret = cgroup_kn_set_ugid(kn);
3856 	if (ret) {
3857 		kernfs_remove(kn);
3858 		return ret;
3859 	}
3860 
3861 	if (cft->file_offset) {
3862 		struct cgroup_file *cfile = (void *)css + cft->file_offset;
3863 
3864 		timer_setup(&cfile->notify_timer, cgroup_file_notify_timer, 0);
3865 
3866 		spin_lock_irq(&cgroup_file_kn_lock);
3867 		cfile->kn = kn;
3868 		spin_unlock_irq(&cgroup_file_kn_lock);
3869 	}
3870 
3871 	if (cft->flags & CFTYPE_SYMLINKED) {
3872 		kn_link = kernfs_create_link(cgrp->kn,
3873 					     cgroup_link_name(cgrp, cft, name),
3874 					     kn);
3875 		if (IS_ERR(kn_link))
3876 			return PTR_ERR(kn_link);
3877 	}
3878 
3879 	return 0;
3880 }
3881 
3882 /**
3883  * cgroup_addrm_files - add or remove files to a cgroup directory
3884  * @css: the target css
3885  * @cgrp: the target cgroup (usually css->cgroup)
3886  * @cfts: array of cftypes to be added
3887  * @is_add: whether to add or remove
3888  *
3889  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3890  * For removals, this function never fails.
3891  */
3892 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3893 			      struct cgroup *cgrp, struct cftype cfts[],
3894 			      bool is_add)
3895 {
3896 	struct cftype *cft, *cft_end = NULL;
3897 	int ret = 0;
3898 
3899 	lockdep_assert_held(&cgroup_mutex);
3900 
3901 restart:
3902 	for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3903 		/* does cft->flags tell us to skip this file on @cgrp? */
3904 		if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3905 			continue;
3906 		if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3907 			continue;
3908 		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3909 			continue;
3910 		if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3911 			continue;
3912 		if ((cft->flags & CFTYPE_DEBUG) && !cgroup_debug)
3913 			continue;
3914 		if (is_add) {
3915 			ret = cgroup_add_file(css, cgrp, cft);
3916 			if (ret) {
3917 				pr_warn("%s: failed to add %s, err=%d\n",
3918 					__func__, cft->name, ret);
3919 				cft_end = cft;
3920 				is_add = false;
3921 				goto restart;
3922 			}
3923 		} else {
3924 			cgroup_rm_file(cgrp, cft);
3925 		}
3926 	}
3927 	return ret;
3928 }
3929 
3930 static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3931 {
3932 	struct cgroup_subsys *ss = cfts[0].ss;
3933 	struct cgroup *root = &ss->root->cgrp;
3934 	struct cgroup_subsys_state *css;
3935 	int ret = 0;
3936 
3937 	lockdep_assert_held(&cgroup_mutex);
3938 
3939 	/* add/rm files for all cgroups created before */
3940 	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3941 		struct cgroup *cgrp = css->cgroup;
3942 
3943 		if (!(css->flags & CSS_VISIBLE))
3944 			continue;
3945 
3946 		ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3947 		if (ret)
3948 			break;
3949 	}
3950 
3951 	if (is_add && !ret)
3952 		kernfs_activate(root->kn);
3953 	return ret;
3954 }
3955 
3956 static void cgroup_exit_cftypes(struct cftype *cfts)
3957 {
3958 	struct cftype *cft;
3959 
3960 	for (cft = cfts; cft->name[0] != '\0'; cft++) {
3961 		/* free copy for custom atomic_write_len, see init_cftypes() */
3962 		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3963 			kfree(cft->kf_ops);
3964 		cft->kf_ops = NULL;
3965 		cft->ss = NULL;
3966 
3967 		/* revert flags set by cgroup core while adding @cfts */
3968 		cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3969 	}
3970 }
3971 
3972 static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3973 {
3974 	struct cftype *cft;
3975 
3976 	for (cft = cfts; cft->name[0] != '\0'; cft++) {
3977 		struct kernfs_ops *kf_ops;
3978 
3979 		WARN_ON(cft->ss || cft->kf_ops);
3980 
3981 		if (cft->seq_start)
3982 			kf_ops = &cgroup_kf_ops;
3983 		else
3984 			kf_ops = &cgroup_kf_single_ops;
3985 
3986 		/*
3987 		 * Ugh... if @cft wants a custom max_write_len, we need to
3988 		 * make a copy of kf_ops to set its atomic_write_len.
3989 		 */
3990 		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
3991 			kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
3992 			if (!kf_ops) {
3993 				cgroup_exit_cftypes(cfts);
3994 				return -ENOMEM;
3995 			}
3996 			kf_ops->atomic_write_len = cft->max_write_len;
3997 		}
3998 
3999 		cft->kf_ops = kf_ops;
4000 		cft->ss = ss;
4001 	}
4002 
4003 	return 0;
4004 }
4005 
4006 static int cgroup_rm_cftypes_locked(struct cftype *cfts)
4007 {
4008 	lockdep_assert_held(&cgroup_mutex);
4009 
4010 	if (!cfts || !cfts[0].ss)
4011 		return -ENOENT;
4012 
4013 	list_del(&cfts->node);
4014 	cgroup_apply_cftypes(cfts, false);
4015 	cgroup_exit_cftypes(cfts);
4016 	return 0;
4017 }
4018 
4019 /**
4020  * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
4021  * @cfts: zero-length name terminated array of cftypes
4022  *
4023  * Unregister @cfts.  Files described by @cfts are removed from all
4024  * existing cgroups and all future cgroups won't have them either.  This
4025  * function can be called anytime whether @cfts' subsys is attached or not.
4026  *
4027  * Returns 0 on successful unregistration, -ENOENT if @cfts is not
4028  * registered.
4029  */
4030 int cgroup_rm_cftypes(struct cftype *cfts)
4031 {
4032 	int ret;
4033 
4034 	mutex_lock(&cgroup_mutex);
4035 	ret = cgroup_rm_cftypes_locked(cfts);
4036 	mutex_unlock(&cgroup_mutex);
4037 	return ret;
4038 }
4039 
4040 /**
4041  * cgroup_add_cftypes - add an array of cftypes to a subsystem
4042  * @ss: target cgroup subsystem
4043  * @cfts: zero-length name terminated array of cftypes
4044  *
4045  * Register @cfts to @ss.  Files described by @cfts are created for all
4046  * existing cgroups to which @ss is attached and all future cgroups will
4047  * have them too.  This function can be called anytime whether @ss is
4048  * attached or not.
4049  *
4050  * Returns 0 on successful registration, -errno on failure.  Note that this
4051  * function currently returns 0 as long as @cfts registration is successful
4052  * even if some file creation attempts on existing cgroups fail.
4053  */
4054 static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4055 {
4056 	int ret;
4057 
4058 	if (!cgroup_ssid_enabled(ss->id))
4059 		return 0;
4060 
4061 	if (!cfts || cfts[0].name[0] == '\0')
4062 		return 0;
4063 
4064 	ret = cgroup_init_cftypes(ss, cfts);
4065 	if (ret)
4066 		return ret;
4067 
4068 	mutex_lock(&cgroup_mutex);
4069 
4070 	list_add_tail(&cfts->node, &ss->cfts);
4071 	ret = cgroup_apply_cftypes(cfts, true);
4072 	if (ret)
4073 		cgroup_rm_cftypes_locked(cfts);
4074 
4075 	mutex_unlock(&cgroup_mutex);
4076 	return ret;
4077 }
4078 
4079 /**
4080  * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
4081  * @ss: target cgroup subsystem
4082  * @cfts: zero-length name terminated array of cftypes
4083  *
4084  * Similar to cgroup_add_cftypes() but the added files are only used for
4085  * the default hierarchy.
4086  */
4087 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4088 {
4089 	struct cftype *cft;
4090 
4091 	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
4092 		cft->flags |= __CFTYPE_ONLY_ON_DFL;
4093 	return cgroup_add_cftypes(ss, cfts);
4094 }
4095 
4096 /**
4097  * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
4098  * @ss: target cgroup subsystem
4099  * @cfts: zero-length name terminated array of cftypes
4100  *
4101  * Similar to cgroup_add_cftypes() but the added files are only used for
4102  * the legacy hierarchies.
4103  */
4104 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4105 {
4106 	struct cftype *cft;
4107 
4108 	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
4109 		cft->flags |= __CFTYPE_NOT_ON_DFL;
4110 	return cgroup_add_cftypes(ss, cfts);
4111 }
4112 
4113 /**
4114  * cgroup_file_notify - generate a file modified event for a cgroup_file
4115  * @cfile: target cgroup_file
4116  *
4117  * @cfile must have been obtained by setting cftype->file_offset.
4118  */
4119 void cgroup_file_notify(struct cgroup_file *cfile)
4120 {
4121 	unsigned long flags;
4122 
4123 	spin_lock_irqsave(&cgroup_file_kn_lock, flags);
4124 	if (cfile->kn) {
4125 		unsigned long last = cfile->notified_at;
4126 		unsigned long next = last + CGROUP_FILE_NOTIFY_MIN_INTV;
4127 
4128 		if (time_in_range(jiffies, last, next)) {
4129 			timer_reduce(&cfile->notify_timer, next);
4130 		} else {
4131 			kernfs_notify(cfile->kn);
4132 			cfile->notified_at = jiffies;
4133 		}
4134 	}
4135 	spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
4136 }
4137 
4138 /**
4139  * css_next_child - find the next child of a given css
4140  * @pos: the current position (%NULL to initiate traversal)
4141  * @parent: css whose children to walk
4142  *
4143  * This function returns the next child of @parent and should be called
4144  * under either cgroup_mutex or RCU read lock.  The only requirement is
4145  * that @parent and @pos are accessible.  The next sibling is guaranteed to
4146  * be returned regardless of their states.
4147  *
4148  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4149  * css which finished ->css_online() is guaranteed to be visible in the
4150  * future iterations and will stay visible until the last reference is put.
4151  * A css which hasn't finished ->css_online() or already finished
4152  * ->css_offline() may show up during traversal.  It's each subsystem's
4153  * responsibility to synchronize against on/offlining.
4154  */
4155 struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
4156 					   struct cgroup_subsys_state *parent)
4157 {
4158 	struct cgroup_subsys_state *next;
4159 
4160 	cgroup_assert_mutex_or_rcu_locked();
4161 
4162 	/*
4163 	 * @pos could already have been unlinked from the sibling list.
4164 	 * Once a cgroup is removed, its ->sibling.next is no longer
4165 	 * updated when its next sibling changes.  CSS_RELEASED is set when
4166 	 * @pos is taken off list, at which time its next pointer is valid,
4167 	 * and, as releases are serialized, the one pointed to by the next
4168 	 * pointer is guaranteed to not have started release yet.  This
4169 	 * implies that if we observe !CSS_RELEASED on @pos in this RCU
4170 	 * critical section, the one pointed to by its next pointer is
4171 	 * guaranteed to not have finished its RCU grace period even if we
4172 	 * have dropped rcu_read_lock() inbetween iterations.
4173 	 *
4174 	 * If @pos has CSS_RELEASED set, its next pointer can't be
4175 	 * dereferenced; however, as each css is given a monotonically
4176 	 * increasing unique serial number and always appended to the
4177 	 * sibling list, the next one can be found by walking the parent's
4178 	 * children until the first css with higher serial number than
4179 	 * @pos's.  While this path can be slower, it happens iff iteration
4180 	 * races against release and the race window is very small.
4181 	 */
4182 	if (!pos) {
4183 		next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
4184 	} else if (likely(!(pos->flags & CSS_RELEASED))) {
4185 		next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
4186 	} else {
4187 		list_for_each_entry_rcu(next, &parent->children, sibling)
4188 			if (next->serial_nr > pos->serial_nr)
4189 				break;
4190 	}
4191 
4192 	/*
4193 	 * @next, if not pointing to the head, can be dereferenced and is
4194 	 * the next sibling.
4195 	 */
4196 	if (&next->sibling != &parent->children)
4197 		return next;
4198 	return NULL;
4199 }
4200 
4201 /**
4202  * css_next_descendant_pre - find the next descendant for pre-order walk
4203  * @pos: the current position (%NULL to initiate traversal)
4204  * @root: css whose descendants to walk
4205  *
4206  * To be used by css_for_each_descendant_pre().  Find the next descendant
4207  * to visit for pre-order traversal of @root's descendants.  @root is
4208  * included in the iteration and the first node to be visited.
4209  *
4210  * While this function requires cgroup_mutex or RCU read locking, it
4211  * doesn't require the whole traversal to be contained in a single critical
4212  * section.  This function will return the correct next descendant as long
4213  * as both @pos and @root are accessible and @pos is a descendant of @root.
4214  *
4215  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4216  * css which finished ->css_online() is guaranteed to be visible in the
4217  * future iterations and will stay visible until the last reference is put.
4218  * A css which hasn't finished ->css_online() or already finished
4219  * ->css_offline() may show up during traversal.  It's each subsystem's
4220  * responsibility to synchronize against on/offlining.
4221  */
4222 struct cgroup_subsys_state *
4223 css_next_descendant_pre(struct cgroup_subsys_state *pos,
4224 			struct cgroup_subsys_state *root)
4225 {
4226 	struct cgroup_subsys_state *next;
4227 
4228 	cgroup_assert_mutex_or_rcu_locked();
4229 
4230 	/* if first iteration, visit @root */
4231 	if (!pos)
4232 		return root;
4233 
4234 	/* visit the first child if exists */
4235 	next = css_next_child(NULL, pos);
4236 	if (next)
4237 		return next;
4238 
4239 	/* no child, visit my or the closest ancestor's next sibling */
4240 	while (pos != root) {
4241 		next = css_next_child(pos, pos->parent);
4242 		if (next)
4243 			return next;
4244 		pos = pos->parent;
4245 	}
4246 
4247 	return NULL;
4248 }
4249 
4250 /**
4251  * css_rightmost_descendant - return the rightmost descendant of a css
4252  * @pos: css of interest
4253  *
4254  * Return the rightmost descendant of @pos.  If there's no descendant, @pos
4255  * is returned.  This can be used during pre-order traversal to skip
4256  * subtree of @pos.
4257  *
4258  * While this function requires cgroup_mutex or RCU read locking, it
4259  * doesn't require the whole traversal to be contained in a single critical
4260  * section.  This function will return the correct rightmost descendant as
4261  * long as @pos is accessible.
4262  */
4263 struct cgroup_subsys_state *
4264 css_rightmost_descendant(struct cgroup_subsys_state *pos)
4265 {
4266 	struct cgroup_subsys_state *last, *tmp;
4267 
4268 	cgroup_assert_mutex_or_rcu_locked();
4269 
4270 	do {
4271 		last = pos;
4272 		/* ->prev isn't RCU safe, walk ->next till the end */
4273 		pos = NULL;
4274 		css_for_each_child(tmp, last)
4275 			pos = tmp;
4276 	} while (pos);
4277 
4278 	return last;
4279 }
4280 
4281 static struct cgroup_subsys_state *
4282 css_leftmost_descendant(struct cgroup_subsys_state *pos)
4283 {
4284 	struct cgroup_subsys_state *last;
4285 
4286 	do {
4287 		last = pos;
4288 		pos = css_next_child(NULL, pos);
4289 	} while (pos);
4290 
4291 	return last;
4292 }
4293 
4294 /**
4295  * css_next_descendant_post - find the next descendant for post-order walk
4296  * @pos: the current position (%NULL to initiate traversal)
4297  * @root: css whose descendants to walk
4298  *
4299  * To be used by css_for_each_descendant_post().  Find the next descendant
4300  * to visit for post-order traversal of @root's descendants.  @root is
4301  * included in the iteration and the last node to be visited.
4302  *
4303  * While this function requires cgroup_mutex or RCU read locking, it
4304  * doesn't require the whole traversal to be contained in a single critical
4305  * section.  This function will return the correct next descendant as long
4306  * as both @pos and @cgroup are accessible and @pos is a descendant of
4307  * @cgroup.
4308  *
4309  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4310  * css which finished ->css_online() is guaranteed to be visible in the
4311  * future iterations and will stay visible until the last reference is put.
4312  * A css which hasn't finished ->css_online() or already finished
4313  * ->css_offline() may show up during traversal.  It's each subsystem's
4314  * responsibility to synchronize against on/offlining.
4315  */
4316 struct cgroup_subsys_state *
4317 css_next_descendant_post(struct cgroup_subsys_state *pos,
4318 			 struct cgroup_subsys_state *root)
4319 {
4320 	struct cgroup_subsys_state *next;
4321 
4322 	cgroup_assert_mutex_or_rcu_locked();
4323 
4324 	/* if first iteration, visit leftmost descendant which may be @root */
4325 	if (!pos)
4326 		return css_leftmost_descendant(root);
4327 
4328 	/* if we visited @root, we're done */
4329 	if (pos == root)
4330 		return NULL;
4331 
4332 	/* if there's an unvisited sibling, visit its leftmost descendant */
4333 	next = css_next_child(pos, pos->parent);
4334 	if (next)
4335 		return css_leftmost_descendant(next);
4336 
4337 	/* no sibling left, visit parent */
4338 	return pos->parent;
4339 }
4340 
4341 /**
4342  * css_has_online_children - does a css have online children
4343  * @css: the target css
4344  *
4345  * Returns %true if @css has any online children; otherwise, %false.  This
4346  * function can be called from any context but the caller is responsible
4347  * for synchronizing against on/offlining as necessary.
4348  */
4349 bool css_has_online_children(struct cgroup_subsys_state *css)
4350 {
4351 	struct cgroup_subsys_state *child;
4352 	bool ret = false;
4353 
4354 	rcu_read_lock();
4355 	css_for_each_child(child, css) {
4356 		if (child->flags & CSS_ONLINE) {
4357 			ret = true;
4358 			break;
4359 		}
4360 	}
4361 	rcu_read_unlock();
4362 	return ret;
4363 }
4364 
4365 static struct css_set *css_task_iter_next_css_set(struct css_task_iter *it)
4366 {
4367 	struct list_head *l;
4368 	struct cgrp_cset_link *link;
4369 	struct css_set *cset;
4370 
4371 	lockdep_assert_held(&css_set_lock);
4372 
4373 	/* find the next threaded cset */
4374 	if (it->tcset_pos) {
4375 		l = it->tcset_pos->next;
4376 
4377 		if (l != it->tcset_head) {
4378 			it->tcset_pos = l;
4379 			return container_of(l, struct css_set,
4380 					    threaded_csets_node);
4381 		}
4382 
4383 		it->tcset_pos = NULL;
4384 	}
4385 
4386 	/* find the next cset */
4387 	l = it->cset_pos;
4388 	l = l->next;
4389 	if (l == it->cset_head) {
4390 		it->cset_pos = NULL;
4391 		return NULL;
4392 	}
4393 
4394 	if (it->ss) {
4395 		cset = container_of(l, struct css_set, e_cset_node[it->ss->id]);
4396 	} else {
4397 		link = list_entry(l, struct cgrp_cset_link, cset_link);
4398 		cset = link->cset;
4399 	}
4400 
4401 	it->cset_pos = l;
4402 
4403 	/* initialize threaded css_set walking */
4404 	if (it->flags & CSS_TASK_ITER_THREADED) {
4405 		if (it->cur_dcset)
4406 			put_css_set_locked(it->cur_dcset);
4407 		it->cur_dcset = cset;
4408 		get_css_set(cset);
4409 
4410 		it->tcset_head = &cset->threaded_csets;
4411 		it->tcset_pos = &cset->threaded_csets;
4412 	}
4413 
4414 	return cset;
4415 }
4416 
4417 /**
4418  * css_task_iter_advance_css_set - advance a task itererator to the next css_set
4419  * @it: the iterator to advance
4420  *
4421  * Advance @it to the next css_set to walk.
4422  */
4423 static void css_task_iter_advance_css_set(struct css_task_iter *it)
4424 {
4425 	struct css_set *cset;
4426 
4427 	lockdep_assert_held(&css_set_lock);
4428 
4429 	/* Advance to the next non-empty css_set */
4430 	do {
4431 		cset = css_task_iter_next_css_set(it);
4432 		if (!cset) {
4433 			it->task_pos = NULL;
4434 			return;
4435 		}
4436 	} while (!css_set_populated(cset));
4437 
4438 	if (!list_empty(&cset->tasks))
4439 		it->task_pos = cset->tasks.next;
4440 	else
4441 		it->task_pos = cset->mg_tasks.next;
4442 
4443 	it->tasks_head = &cset->tasks;
4444 	it->mg_tasks_head = &cset->mg_tasks;
4445 
4446 	/*
4447 	 * We don't keep css_sets locked across iteration steps and thus
4448 	 * need to take steps to ensure that iteration can be resumed after
4449 	 * the lock is re-acquired.  Iteration is performed at two levels -
4450 	 * css_sets and tasks in them.
4451 	 *
4452 	 * Once created, a css_set never leaves its cgroup lists, so a
4453 	 * pinned css_set is guaranteed to stay put and we can resume
4454 	 * iteration afterwards.
4455 	 *
4456 	 * Tasks may leave @cset across iteration steps.  This is resolved
4457 	 * by registering each iterator with the css_set currently being
4458 	 * walked and making css_set_move_task() advance iterators whose
4459 	 * next task is leaving.
4460 	 */
4461 	if (it->cur_cset) {
4462 		list_del(&it->iters_node);
4463 		put_css_set_locked(it->cur_cset);
4464 	}
4465 	get_css_set(cset);
4466 	it->cur_cset = cset;
4467 	list_add(&it->iters_node, &cset->task_iters);
4468 }
4469 
4470 static void css_task_iter_advance(struct css_task_iter *it)
4471 {
4472 	struct list_head *next;
4473 
4474 	lockdep_assert_held(&css_set_lock);
4475 repeat:
4476 	if (it->task_pos) {
4477 		/*
4478 		 * Advance iterator to find next entry.  cset->tasks is
4479 		 * consumed first and then ->mg_tasks.  After ->mg_tasks,
4480 		 * we move onto the next cset.
4481 		 */
4482 		next = it->task_pos->next;
4483 
4484 		if (next == it->tasks_head)
4485 			next = it->mg_tasks_head->next;
4486 
4487 		if (next == it->mg_tasks_head)
4488 			css_task_iter_advance_css_set(it);
4489 		else
4490 			it->task_pos = next;
4491 	} else {
4492 		/* called from start, proceed to the first cset */
4493 		css_task_iter_advance_css_set(it);
4494 	}
4495 
4496 	/* if PROCS, skip over tasks which aren't group leaders */
4497 	if ((it->flags & CSS_TASK_ITER_PROCS) && it->task_pos &&
4498 	    !thread_group_leader(list_entry(it->task_pos, struct task_struct,
4499 					    cg_list)))
4500 		goto repeat;
4501 }
4502 
4503 /**
4504  * css_task_iter_start - initiate task iteration
4505  * @css: the css to walk tasks of
4506  * @flags: CSS_TASK_ITER_* flags
4507  * @it: the task iterator to use
4508  *
4509  * Initiate iteration through the tasks of @css.  The caller can call
4510  * css_task_iter_next() to walk through the tasks until the function
4511  * returns NULL.  On completion of iteration, css_task_iter_end() must be
4512  * called.
4513  */
4514 void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
4515 			 struct css_task_iter *it)
4516 {
4517 	/* no one should try to iterate before mounting cgroups */
4518 	WARN_ON_ONCE(!use_task_css_set_links);
4519 
4520 	memset(it, 0, sizeof(*it));
4521 
4522 	spin_lock_irq(&css_set_lock);
4523 
4524 	it->ss = css->ss;
4525 	it->flags = flags;
4526 
4527 	if (it->ss)
4528 		it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4529 	else
4530 		it->cset_pos = &css->cgroup->cset_links;
4531 
4532 	it->cset_head = it->cset_pos;
4533 
4534 	css_task_iter_advance(it);
4535 
4536 	spin_unlock_irq(&css_set_lock);
4537 }
4538 
4539 /**
4540  * css_task_iter_next - return the next task for the iterator
4541  * @it: the task iterator being iterated
4542  *
4543  * The "next" function for task iteration.  @it should have been
4544  * initialized via css_task_iter_start().  Returns NULL when the iteration
4545  * reaches the end.
4546  */
4547 struct task_struct *css_task_iter_next(struct css_task_iter *it)
4548 {
4549 	if (it->cur_task) {
4550 		put_task_struct(it->cur_task);
4551 		it->cur_task = NULL;
4552 	}
4553 
4554 	spin_lock_irq(&css_set_lock);
4555 
4556 	if (it->task_pos) {
4557 		it->cur_task = list_entry(it->task_pos, struct task_struct,
4558 					  cg_list);
4559 		get_task_struct(it->cur_task);
4560 		css_task_iter_advance(it);
4561 	}
4562 
4563 	spin_unlock_irq(&css_set_lock);
4564 
4565 	return it->cur_task;
4566 }
4567 
4568 /**
4569  * css_task_iter_end - finish task iteration
4570  * @it: the task iterator to finish
4571  *
4572  * Finish task iteration started by css_task_iter_start().
4573  */
4574 void css_task_iter_end(struct css_task_iter *it)
4575 {
4576 	if (it->cur_cset) {
4577 		spin_lock_irq(&css_set_lock);
4578 		list_del(&it->iters_node);
4579 		put_css_set_locked(it->cur_cset);
4580 		spin_unlock_irq(&css_set_lock);
4581 	}
4582 
4583 	if (it->cur_dcset)
4584 		put_css_set(it->cur_dcset);
4585 
4586 	if (it->cur_task)
4587 		put_task_struct(it->cur_task);
4588 }
4589 
4590 static void cgroup_procs_release(struct kernfs_open_file *of)
4591 {
4592 	if (of->priv) {
4593 		css_task_iter_end(of->priv);
4594 		kfree(of->priv);
4595 	}
4596 }
4597 
4598 static void *cgroup_procs_next(struct seq_file *s, void *v, loff_t *pos)
4599 {
4600 	struct kernfs_open_file *of = s->private;
4601 	struct css_task_iter *it = of->priv;
4602 
4603 	return css_task_iter_next(it);
4604 }
4605 
4606 static void *__cgroup_procs_start(struct seq_file *s, loff_t *pos,
4607 				  unsigned int iter_flags)
4608 {
4609 	struct kernfs_open_file *of = s->private;
4610 	struct cgroup *cgrp = seq_css(s)->cgroup;
4611 	struct css_task_iter *it = of->priv;
4612 
4613 	/*
4614 	 * When a seq_file is seeked, it's always traversed sequentially
4615 	 * from position 0, so we can simply keep iterating on !0 *pos.
4616 	 */
4617 	if (!it) {
4618 		if (WARN_ON_ONCE((*pos)++))
4619 			return ERR_PTR(-EINVAL);
4620 
4621 		it = kzalloc(sizeof(*it), GFP_KERNEL);
4622 		if (!it)
4623 			return ERR_PTR(-ENOMEM);
4624 		of->priv = it;
4625 		css_task_iter_start(&cgrp->self, iter_flags, it);
4626 	} else if (!(*pos)++) {
4627 		css_task_iter_end(it);
4628 		css_task_iter_start(&cgrp->self, iter_flags, it);
4629 	}
4630 
4631 	return cgroup_procs_next(s, NULL, NULL);
4632 }
4633 
4634 static void *cgroup_procs_start(struct seq_file *s, loff_t *pos)
4635 {
4636 	struct cgroup *cgrp = seq_css(s)->cgroup;
4637 
4638 	/*
4639 	 * All processes of a threaded subtree belong to the domain cgroup
4640 	 * of the subtree.  Only threads can be distributed across the
4641 	 * subtree.  Reject reads on cgroup.procs in the subtree proper.
4642 	 * They're always empty anyway.
4643 	 */
4644 	if (cgroup_is_threaded(cgrp))
4645 		return ERR_PTR(-EOPNOTSUPP);
4646 
4647 	return __cgroup_procs_start(s, pos, CSS_TASK_ITER_PROCS |
4648 					    CSS_TASK_ITER_THREADED);
4649 }
4650 
4651 static int cgroup_procs_show(struct seq_file *s, void *v)
4652 {
4653 	seq_printf(s, "%d\n", task_pid_vnr(v));
4654 	return 0;
4655 }
4656 
4657 static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
4658 					 struct cgroup *dst_cgrp,
4659 					 struct super_block *sb)
4660 {
4661 	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
4662 	struct cgroup *com_cgrp = src_cgrp;
4663 	struct inode *inode;
4664 	int ret;
4665 
4666 	lockdep_assert_held(&cgroup_mutex);
4667 
4668 	/* find the common ancestor */
4669 	while (!cgroup_is_descendant(dst_cgrp, com_cgrp))
4670 		com_cgrp = cgroup_parent(com_cgrp);
4671 
4672 	/* %current should be authorized to migrate to the common ancestor */
4673 	inode = kernfs_get_inode(sb, com_cgrp->procs_file.kn);
4674 	if (!inode)
4675 		return -ENOMEM;
4676 
4677 	ret = inode_permission(inode, MAY_WRITE);
4678 	iput(inode);
4679 	if (ret)
4680 		return ret;
4681 
4682 	/*
4683 	 * If namespaces are delegation boundaries, %current must be able
4684 	 * to see both source and destination cgroups from its namespace.
4685 	 */
4686 	if ((cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) &&
4687 	    (!cgroup_is_descendant(src_cgrp, ns->root_cset->dfl_cgrp) ||
4688 	     !cgroup_is_descendant(dst_cgrp, ns->root_cset->dfl_cgrp)))
4689 		return -ENOENT;
4690 
4691 	return 0;
4692 }
4693 
4694 static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
4695 				  char *buf, size_t nbytes, loff_t off)
4696 {
4697 	struct cgroup *src_cgrp, *dst_cgrp;
4698 	struct task_struct *task;
4699 	ssize_t ret;
4700 
4701 	dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4702 	if (!dst_cgrp)
4703 		return -ENODEV;
4704 
4705 	task = cgroup_procs_write_start(buf, true);
4706 	ret = PTR_ERR_OR_ZERO(task);
4707 	if (ret)
4708 		goto out_unlock;
4709 
4710 	/* find the source cgroup */
4711 	spin_lock_irq(&css_set_lock);
4712 	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4713 	spin_unlock_irq(&css_set_lock);
4714 
4715 	ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
4716 					    of->file->f_path.dentry->d_sb);
4717 	if (ret)
4718 		goto out_finish;
4719 
4720 	ret = cgroup_attach_task(dst_cgrp, task, true);
4721 
4722 out_finish:
4723 	cgroup_procs_write_finish(task);
4724 out_unlock:
4725 	cgroup_kn_unlock(of->kn);
4726 
4727 	return ret ?: nbytes;
4728 }
4729 
4730 static void *cgroup_threads_start(struct seq_file *s, loff_t *pos)
4731 {
4732 	return __cgroup_procs_start(s, pos, 0);
4733 }
4734 
4735 static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
4736 				    char *buf, size_t nbytes, loff_t off)
4737 {
4738 	struct cgroup *src_cgrp, *dst_cgrp;
4739 	struct task_struct *task;
4740 	ssize_t ret;
4741 
4742 	buf = strstrip(buf);
4743 
4744 	dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4745 	if (!dst_cgrp)
4746 		return -ENODEV;
4747 
4748 	task = cgroup_procs_write_start(buf, false);
4749 	ret = PTR_ERR_OR_ZERO(task);
4750 	if (ret)
4751 		goto out_unlock;
4752 
4753 	/* find the source cgroup */
4754 	spin_lock_irq(&css_set_lock);
4755 	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4756 	spin_unlock_irq(&css_set_lock);
4757 
4758 	/* thread migrations follow the cgroup.procs delegation rule */
4759 	ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
4760 					    of->file->f_path.dentry->d_sb);
4761 	if (ret)
4762 		goto out_finish;
4763 
4764 	/* and must be contained in the same domain */
4765 	ret = -EOPNOTSUPP;
4766 	if (src_cgrp->dom_cgrp != dst_cgrp->dom_cgrp)
4767 		goto out_finish;
4768 
4769 	ret = cgroup_attach_task(dst_cgrp, task, false);
4770 
4771 out_finish:
4772 	cgroup_procs_write_finish(task);
4773 out_unlock:
4774 	cgroup_kn_unlock(of->kn);
4775 
4776 	return ret ?: nbytes;
4777 }
4778 
4779 /* cgroup core interface files for the default hierarchy */
4780 static struct cftype cgroup_base_files[] = {
4781 	{
4782 		.name = "cgroup.type",
4783 		.flags = CFTYPE_NOT_ON_ROOT,
4784 		.seq_show = cgroup_type_show,
4785 		.write = cgroup_type_write,
4786 	},
4787 	{
4788 		.name = "cgroup.procs",
4789 		.flags = CFTYPE_NS_DELEGATABLE,
4790 		.file_offset = offsetof(struct cgroup, procs_file),
4791 		.release = cgroup_procs_release,
4792 		.seq_start = cgroup_procs_start,
4793 		.seq_next = cgroup_procs_next,
4794 		.seq_show = cgroup_procs_show,
4795 		.write = cgroup_procs_write,
4796 	},
4797 	{
4798 		.name = "cgroup.threads",
4799 		.flags = CFTYPE_NS_DELEGATABLE,
4800 		.release = cgroup_procs_release,
4801 		.seq_start = cgroup_threads_start,
4802 		.seq_next = cgroup_procs_next,
4803 		.seq_show = cgroup_procs_show,
4804 		.write = cgroup_threads_write,
4805 	},
4806 	{
4807 		.name = "cgroup.controllers",
4808 		.seq_show = cgroup_controllers_show,
4809 	},
4810 	{
4811 		.name = "cgroup.subtree_control",
4812 		.flags = CFTYPE_NS_DELEGATABLE,
4813 		.seq_show = cgroup_subtree_control_show,
4814 		.write = cgroup_subtree_control_write,
4815 	},
4816 	{
4817 		.name = "cgroup.events",
4818 		.flags = CFTYPE_NOT_ON_ROOT,
4819 		.file_offset = offsetof(struct cgroup, events_file),
4820 		.seq_show = cgroup_events_show,
4821 	},
4822 	{
4823 		.name = "cgroup.max.descendants",
4824 		.seq_show = cgroup_max_descendants_show,
4825 		.write = cgroup_max_descendants_write,
4826 	},
4827 	{
4828 		.name = "cgroup.max.depth",
4829 		.seq_show = cgroup_max_depth_show,
4830 		.write = cgroup_max_depth_write,
4831 	},
4832 	{
4833 		.name = "cgroup.stat",
4834 		.seq_show = cgroup_stat_show,
4835 	},
4836 	{
4837 		.name = "cgroup.freeze",
4838 		.flags = CFTYPE_NOT_ON_ROOT,
4839 		.seq_show = cgroup_freeze_show,
4840 		.write = cgroup_freeze_write,
4841 	},
4842 	{
4843 		.name = "cpu.stat",
4844 		.flags = CFTYPE_NOT_ON_ROOT,
4845 		.seq_show = cpu_stat_show,
4846 	},
4847 #ifdef CONFIG_PSI
4848 	{
4849 		.name = "io.pressure",
4850 		.seq_show = cgroup_io_pressure_show,
4851 		.write = cgroup_io_pressure_write,
4852 		.poll = cgroup_pressure_poll,
4853 		.release = cgroup_pressure_release,
4854 	},
4855 	{
4856 		.name = "memory.pressure",
4857 		.seq_show = cgroup_memory_pressure_show,
4858 		.write = cgroup_memory_pressure_write,
4859 		.poll = cgroup_pressure_poll,
4860 		.release = cgroup_pressure_release,
4861 	},
4862 	{
4863 		.name = "cpu.pressure",
4864 		.seq_show = cgroup_cpu_pressure_show,
4865 		.write = cgroup_cpu_pressure_write,
4866 		.poll = cgroup_pressure_poll,
4867 		.release = cgroup_pressure_release,
4868 	},
4869 #endif /* CONFIG_PSI */
4870 	{ }	/* terminate */
4871 };
4872 
4873 /*
4874  * css destruction is four-stage process.
4875  *
4876  * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4877  *    Implemented in kill_css().
4878  *
4879  * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4880  *    and thus css_tryget_online() is guaranteed to fail, the css can be
4881  *    offlined by invoking offline_css().  After offlining, the base ref is
4882  *    put.  Implemented in css_killed_work_fn().
4883  *
4884  * 3. When the percpu_ref reaches zero, the only possible remaining
4885  *    accessors are inside RCU read sections.  css_release() schedules the
4886  *    RCU callback.
4887  *
4888  * 4. After the grace period, the css can be freed.  Implemented in
4889  *    css_free_work_fn().
4890  *
4891  * It is actually hairier because both step 2 and 4 require process context
4892  * and thus involve punting to css->destroy_work adding two additional
4893  * steps to the already complex sequence.
4894  */
4895 static void css_free_rwork_fn(struct work_struct *work)
4896 {
4897 	struct cgroup_subsys_state *css = container_of(to_rcu_work(work),
4898 				struct cgroup_subsys_state, destroy_rwork);
4899 	struct cgroup_subsys *ss = css->ss;
4900 	struct cgroup *cgrp = css->cgroup;
4901 
4902 	percpu_ref_exit(&css->refcnt);
4903 
4904 	if (ss) {
4905 		/* css free path */
4906 		struct cgroup_subsys_state *parent = css->parent;
4907 		int id = css->id;
4908 
4909 		ss->css_free(css);
4910 		cgroup_idr_remove(&ss->css_idr, id);
4911 		cgroup_put(cgrp);
4912 
4913 		if (parent)
4914 			css_put(parent);
4915 	} else {
4916 		/* cgroup free path */
4917 		atomic_dec(&cgrp->root->nr_cgrps);
4918 		cgroup1_pidlist_destroy_all(cgrp);
4919 		cancel_work_sync(&cgrp->release_agent_work);
4920 
4921 		if (cgroup_parent(cgrp)) {
4922 			/*
4923 			 * We get a ref to the parent, and put the ref when
4924 			 * this cgroup is being freed, so it's guaranteed
4925 			 * that the parent won't be destroyed before its
4926 			 * children.
4927 			 */
4928 			cgroup_put(cgroup_parent(cgrp));
4929 			kernfs_put(cgrp->kn);
4930 			psi_cgroup_free(cgrp);
4931 			if (cgroup_on_dfl(cgrp))
4932 				cgroup_rstat_exit(cgrp);
4933 			kfree(cgrp);
4934 		} else {
4935 			/*
4936 			 * This is root cgroup's refcnt reaching zero,
4937 			 * which indicates that the root should be
4938 			 * released.
4939 			 */
4940 			cgroup_destroy_root(cgrp->root);
4941 		}
4942 	}
4943 }
4944 
4945 static void css_release_work_fn(struct work_struct *work)
4946 {
4947 	struct cgroup_subsys_state *css =
4948 		container_of(work, struct cgroup_subsys_state, destroy_work);
4949 	struct cgroup_subsys *ss = css->ss;
4950 	struct cgroup *cgrp = css->cgroup;
4951 
4952 	mutex_lock(&cgroup_mutex);
4953 
4954 	css->flags |= CSS_RELEASED;
4955 	list_del_rcu(&css->sibling);
4956 
4957 	if (ss) {
4958 		/* css release path */
4959 		if (!list_empty(&css->rstat_css_node)) {
4960 			cgroup_rstat_flush(cgrp);
4961 			list_del_rcu(&css->rstat_css_node);
4962 		}
4963 
4964 		cgroup_idr_replace(&ss->css_idr, NULL, css->id);
4965 		if (ss->css_released)
4966 			ss->css_released(css);
4967 	} else {
4968 		struct cgroup *tcgrp;
4969 
4970 		/* cgroup release path */
4971 		TRACE_CGROUP_PATH(release, cgrp);
4972 
4973 		if (cgroup_on_dfl(cgrp))
4974 			cgroup_rstat_flush(cgrp);
4975 
4976 		spin_lock_irq(&css_set_lock);
4977 		for (tcgrp = cgroup_parent(cgrp); tcgrp;
4978 		     tcgrp = cgroup_parent(tcgrp))
4979 			tcgrp->nr_dying_descendants--;
4980 		spin_unlock_irq(&css_set_lock);
4981 
4982 		cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
4983 		cgrp->id = -1;
4984 
4985 		/*
4986 		 * There are two control paths which try to determine
4987 		 * cgroup from dentry without going through kernfs -
4988 		 * cgroupstats_build() and css_tryget_online_from_dir().
4989 		 * Those are supported by RCU protecting clearing of
4990 		 * cgrp->kn->priv backpointer.
4991 		 */
4992 		if (cgrp->kn)
4993 			RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
4994 					 NULL);
4995 
4996 		cgroup_bpf_put(cgrp);
4997 	}
4998 
4999 	mutex_unlock(&cgroup_mutex);
5000 
5001 	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
5002 	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
5003 }
5004 
5005 static void css_release(struct percpu_ref *ref)
5006 {
5007 	struct cgroup_subsys_state *css =
5008 		container_of(ref, struct cgroup_subsys_state, refcnt);
5009 
5010 	INIT_WORK(&css->destroy_work, css_release_work_fn);
5011 	queue_work(cgroup_destroy_wq, &css->destroy_work);
5012 }
5013 
5014 static void init_and_link_css(struct cgroup_subsys_state *css,
5015 			      struct cgroup_subsys *ss, struct cgroup *cgrp)
5016 {
5017 	lockdep_assert_held(&cgroup_mutex);
5018 
5019 	cgroup_get_live(cgrp);
5020 
5021 	memset(css, 0, sizeof(*css));
5022 	css->cgroup = cgrp;
5023 	css->ss = ss;
5024 	css->id = -1;
5025 	INIT_LIST_HEAD(&css->sibling);
5026 	INIT_LIST_HEAD(&css->children);
5027 	INIT_LIST_HEAD(&css->rstat_css_node);
5028 	css->serial_nr = css_serial_nr_next++;
5029 	atomic_set(&css->online_cnt, 0);
5030 
5031 	if (cgroup_parent(cgrp)) {
5032 		css->parent = cgroup_css(cgroup_parent(cgrp), ss);
5033 		css_get(css->parent);
5034 	}
5035 
5036 	if (cgroup_on_dfl(cgrp) && ss->css_rstat_flush)
5037 		list_add_rcu(&css->rstat_css_node, &cgrp->rstat_css_list);
5038 
5039 	BUG_ON(cgroup_css(cgrp, ss));
5040 }
5041 
5042 /* invoke ->css_online() on a new CSS and mark it online if successful */
5043 static int online_css(struct cgroup_subsys_state *css)
5044 {
5045 	struct cgroup_subsys *ss = css->ss;
5046 	int ret = 0;
5047 
5048 	lockdep_assert_held(&cgroup_mutex);
5049 
5050 	if (ss->css_online)
5051 		ret = ss->css_online(css);
5052 	if (!ret) {
5053 		css->flags |= CSS_ONLINE;
5054 		rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
5055 
5056 		atomic_inc(&css->online_cnt);
5057 		if (css->parent)
5058 			atomic_inc(&css->parent->online_cnt);
5059 	}
5060 	return ret;
5061 }
5062 
5063 /* if the CSS is online, invoke ->css_offline() on it and mark it offline */
5064 static void offline_css(struct cgroup_subsys_state *css)
5065 {
5066 	struct cgroup_subsys *ss = css->ss;
5067 
5068 	lockdep_assert_held(&cgroup_mutex);
5069 
5070 	if (!(css->flags & CSS_ONLINE))
5071 		return;
5072 
5073 	if (ss->css_offline)
5074 		ss->css_offline(css);
5075 
5076 	css->flags &= ~CSS_ONLINE;
5077 	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
5078 
5079 	wake_up_all(&css->cgroup->offline_waitq);
5080 }
5081 
5082 /**
5083  * css_create - create a cgroup_subsys_state
5084  * @cgrp: the cgroup new css will be associated with
5085  * @ss: the subsys of new css
5086  *
5087  * Create a new css associated with @cgrp - @ss pair.  On success, the new
5088  * css is online and installed in @cgrp.  This function doesn't create the
5089  * interface files.  Returns 0 on success, -errno on failure.
5090  */
5091 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
5092 					      struct cgroup_subsys *ss)
5093 {
5094 	struct cgroup *parent = cgroup_parent(cgrp);
5095 	struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
5096 	struct cgroup_subsys_state *css;
5097 	int err;
5098 
5099 	lockdep_assert_held(&cgroup_mutex);
5100 
5101 	css = ss->css_alloc(parent_css);
5102 	if (!css)
5103 		css = ERR_PTR(-ENOMEM);
5104 	if (IS_ERR(css))
5105 		return css;
5106 
5107 	init_and_link_css(css, ss, cgrp);
5108 
5109 	err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
5110 	if (err)
5111 		goto err_free_css;
5112 
5113 	err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
5114 	if (err < 0)
5115 		goto err_free_css;
5116 	css->id = err;
5117 
5118 	/* @css is ready to be brought online now, make it visible */
5119 	list_add_tail_rcu(&css->sibling, &parent_css->children);
5120 	cgroup_idr_replace(&ss->css_idr, css, css->id);
5121 
5122 	err = online_css(css);
5123 	if (err)
5124 		goto err_list_del;
5125 
5126 	if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
5127 	    cgroup_parent(parent)) {
5128 		pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
5129 			current->comm, current->pid, ss->name);
5130 		if (!strcmp(ss->name, "memory"))
5131 			pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
5132 		ss->warned_broken_hierarchy = true;
5133 	}
5134 
5135 	return css;
5136 
5137 err_list_del:
5138 	list_del_rcu(&css->sibling);
5139 err_free_css:
5140 	list_del_rcu(&css->rstat_css_node);
5141 	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
5142 	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
5143 	return ERR_PTR(err);
5144 }
5145 
5146 /*
5147  * The returned cgroup is fully initialized including its control mask, but
5148  * it isn't associated with its kernfs_node and doesn't have the control
5149  * mask applied.
5150  */
5151 static struct cgroup *cgroup_create(struct cgroup *parent)
5152 {
5153 	struct cgroup_root *root = parent->root;
5154 	struct cgroup *cgrp, *tcgrp;
5155 	int level = parent->level + 1;
5156 	int ret;
5157 
5158 	/* allocate the cgroup and its ID, 0 is reserved for the root */
5159 	cgrp = kzalloc(struct_size(cgrp, ancestor_ids, (level + 1)),
5160 		       GFP_KERNEL);
5161 	if (!cgrp)
5162 		return ERR_PTR(-ENOMEM);
5163 
5164 	ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
5165 	if (ret)
5166 		goto out_free_cgrp;
5167 
5168 	if (cgroup_on_dfl(parent)) {
5169 		ret = cgroup_rstat_init(cgrp);
5170 		if (ret)
5171 			goto out_cancel_ref;
5172 	}
5173 
5174 	/*
5175 	 * Temporarily set the pointer to NULL, so idr_find() won't return
5176 	 * a half-baked cgroup.
5177 	 */
5178 	cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
5179 	if (cgrp->id < 0) {
5180 		ret = -ENOMEM;
5181 		goto out_stat_exit;
5182 	}
5183 
5184 	init_cgroup_housekeeping(cgrp);
5185 
5186 	cgrp->self.parent = &parent->self;
5187 	cgrp->root = root;
5188 	cgrp->level = level;
5189 
5190 	ret = psi_cgroup_alloc(cgrp);
5191 	if (ret)
5192 		goto out_idr_free;
5193 
5194 	ret = cgroup_bpf_inherit(cgrp);
5195 	if (ret)
5196 		goto out_psi_free;
5197 
5198 	/*
5199 	 * New cgroup inherits effective freeze counter, and
5200 	 * if the parent has to be frozen, the child has too.
5201 	 */
5202 	cgrp->freezer.e_freeze = parent->freezer.e_freeze;
5203 	if (cgrp->freezer.e_freeze)
5204 		set_bit(CGRP_FROZEN, &cgrp->flags);
5205 
5206 	spin_lock_irq(&css_set_lock);
5207 	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
5208 		cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
5209 
5210 		if (tcgrp != cgrp) {
5211 			tcgrp->nr_descendants++;
5212 
5213 			/*
5214 			 * If the new cgroup is frozen, all ancestor cgroups
5215 			 * get a new frozen descendant, but their state can't
5216 			 * change because of this.
5217 			 */
5218 			if (cgrp->freezer.e_freeze)
5219 				tcgrp->freezer.nr_frozen_descendants++;
5220 		}
5221 	}
5222 	spin_unlock_irq(&css_set_lock);
5223 
5224 	if (notify_on_release(parent))
5225 		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
5226 
5227 	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
5228 		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
5229 
5230 	cgrp->self.serial_nr = css_serial_nr_next++;
5231 
5232 	/* allocation complete, commit to creation */
5233 	list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
5234 	atomic_inc(&root->nr_cgrps);
5235 	cgroup_get_live(parent);
5236 
5237 	/*
5238 	 * @cgrp is now fully operational.  If something fails after this
5239 	 * point, it'll be released via the normal destruction path.
5240 	 */
5241 	cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
5242 
5243 	/*
5244 	 * On the default hierarchy, a child doesn't automatically inherit
5245 	 * subtree_control from the parent.  Each is configured manually.
5246 	 */
5247 	if (!cgroup_on_dfl(cgrp))
5248 		cgrp->subtree_control = cgroup_control(cgrp);
5249 
5250 	cgroup_propagate_control(cgrp);
5251 
5252 	return cgrp;
5253 
5254 out_psi_free:
5255 	psi_cgroup_free(cgrp);
5256 out_idr_free:
5257 	cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
5258 out_stat_exit:
5259 	if (cgroup_on_dfl(parent))
5260 		cgroup_rstat_exit(cgrp);
5261 out_cancel_ref:
5262 	percpu_ref_exit(&cgrp->self.refcnt);
5263 out_free_cgrp:
5264 	kfree(cgrp);
5265 	return ERR_PTR(ret);
5266 }
5267 
5268 static bool cgroup_check_hierarchy_limits(struct cgroup *parent)
5269 {
5270 	struct cgroup *cgroup;
5271 	int ret = false;
5272 	int level = 1;
5273 
5274 	lockdep_assert_held(&cgroup_mutex);
5275 
5276 	for (cgroup = parent; cgroup; cgroup = cgroup_parent(cgroup)) {
5277 		if (cgroup->nr_descendants >= cgroup->max_descendants)
5278 			goto fail;
5279 
5280 		if (level > cgroup->max_depth)
5281 			goto fail;
5282 
5283 		level++;
5284 	}
5285 
5286 	ret = true;
5287 fail:
5288 	return ret;
5289 }
5290 
5291 int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
5292 {
5293 	struct cgroup *parent, *cgrp;
5294 	struct kernfs_node *kn;
5295 	int ret;
5296 
5297 	/* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
5298 	if (strchr(name, '\n'))
5299 		return -EINVAL;
5300 
5301 	parent = cgroup_kn_lock_live(parent_kn, false);
5302 	if (!parent)
5303 		return -ENODEV;
5304 
5305 	if (!cgroup_check_hierarchy_limits(parent)) {
5306 		ret = -EAGAIN;
5307 		goto out_unlock;
5308 	}
5309 
5310 	cgrp = cgroup_create(parent);
5311 	if (IS_ERR(cgrp)) {
5312 		ret = PTR_ERR(cgrp);
5313 		goto out_unlock;
5314 	}
5315 
5316 	/* create the directory */
5317 	kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
5318 	if (IS_ERR(kn)) {
5319 		ret = PTR_ERR(kn);
5320 		goto out_destroy;
5321 	}
5322 	cgrp->kn = kn;
5323 
5324 	/*
5325 	 * This extra ref will be put in cgroup_free_fn() and guarantees
5326 	 * that @cgrp->kn is always accessible.
5327 	 */
5328 	kernfs_get(kn);
5329 
5330 	ret = cgroup_kn_set_ugid(kn);
5331 	if (ret)
5332 		goto out_destroy;
5333 
5334 	ret = css_populate_dir(&cgrp->self);
5335 	if (ret)
5336 		goto out_destroy;
5337 
5338 	ret = cgroup_apply_control_enable(cgrp);
5339 	if (ret)
5340 		goto out_destroy;
5341 
5342 	TRACE_CGROUP_PATH(mkdir, cgrp);
5343 
5344 	/* let's create and online css's */
5345 	kernfs_activate(kn);
5346 
5347 	ret = 0;
5348 	goto out_unlock;
5349 
5350 out_destroy:
5351 	cgroup_destroy_locked(cgrp);
5352 out_unlock:
5353 	cgroup_kn_unlock(parent_kn);
5354 	return ret;
5355 }
5356 
5357 /*
5358  * This is called when the refcnt of a css is confirmed to be killed.
5359  * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
5360  * initate destruction and put the css ref from kill_css().
5361  */
5362 static void css_killed_work_fn(struct work_struct *work)
5363 {
5364 	struct cgroup_subsys_state *css =
5365 		container_of(work, struct cgroup_subsys_state, destroy_work);
5366 
5367 	mutex_lock(&cgroup_mutex);
5368 
5369 	do {
5370 		offline_css(css);
5371 		css_put(css);
5372 		/* @css can't go away while we're holding cgroup_mutex */
5373 		css = css->parent;
5374 	} while (css && atomic_dec_and_test(&css->online_cnt));
5375 
5376 	mutex_unlock(&cgroup_mutex);
5377 }
5378 
5379 /* css kill confirmation processing requires process context, bounce */
5380 static void css_killed_ref_fn(struct percpu_ref *ref)
5381 {
5382 	struct cgroup_subsys_state *css =
5383 		container_of(ref, struct cgroup_subsys_state, refcnt);
5384 
5385 	if (atomic_dec_and_test(&css->online_cnt)) {
5386 		INIT_WORK(&css->destroy_work, css_killed_work_fn);
5387 		queue_work(cgroup_destroy_wq, &css->destroy_work);
5388 	}
5389 }
5390 
5391 /**
5392  * kill_css - destroy a css
5393  * @css: css to destroy
5394  *
5395  * This function initiates destruction of @css by removing cgroup interface
5396  * files and putting its base reference.  ->css_offline() will be invoked
5397  * asynchronously once css_tryget_online() is guaranteed to fail and when
5398  * the reference count reaches zero, @css will be released.
5399  */
5400 static void kill_css(struct cgroup_subsys_state *css)
5401 {
5402 	lockdep_assert_held(&cgroup_mutex);
5403 
5404 	if (css->flags & CSS_DYING)
5405 		return;
5406 
5407 	css->flags |= CSS_DYING;
5408 
5409 	/*
5410 	 * This must happen before css is disassociated with its cgroup.
5411 	 * See seq_css() for details.
5412 	 */
5413 	css_clear_dir(css);
5414 
5415 	/*
5416 	 * Killing would put the base ref, but we need to keep it alive
5417 	 * until after ->css_offline().
5418 	 */
5419 	css_get(css);
5420 
5421 	/*
5422 	 * cgroup core guarantees that, by the time ->css_offline() is
5423 	 * invoked, no new css reference will be given out via
5424 	 * css_tryget_online().  We can't simply call percpu_ref_kill() and
5425 	 * proceed to offlining css's because percpu_ref_kill() doesn't
5426 	 * guarantee that the ref is seen as killed on all CPUs on return.
5427 	 *
5428 	 * Use percpu_ref_kill_and_confirm() to get notifications as each
5429 	 * css is confirmed to be seen as killed on all CPUs.
5430 	 */
5431 	percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5432 }
5433 
5434 /**
5435  * cgroup_destroy_locked - the first stage of cgroup destruction
5436  * @cgrp: cgroup to be destroyed
5437  *
5438  * css's make use of percpu refcnts whose killing latency shouldn't be
5439  * exposed to userland and are RCU protected.  Also, cgroup core needs to
5440  * guarantee that css_tryget_online() won't succeed by the time
5441  * ->css_offline() is invoked.  To satisfy all the requirements,
5442  * destruction is implemented in the following two steps.
5443  *
5444  * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5445  *     userland visible parts and start killing the percpu refcnts of
5446  *     css's.  Set up so that the next stage will be kicked off once all
5447  *     the percpu refcnts are confirmed to be killed.
5448  *
5449  * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5450  *     rest of destruction.  Once all cgroup references are gone, the
5451  *     cgroup is RCU-freed.
5452  *
5453  * This function implements s1.  After this step, @cgrp is gone as far as
5454  * the userland is concerned and a new cgroup with the same name may be
5455  * created.  As cgroup doesn't care about the names internally, this
5456  * doesn't cause any problem.
5457  */
5458 static int cgroup_destroy_locked(struct cgroup *cgrp)
5459 	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5460 {
5461 	struct cgroup *tcgrp, *parent = cgroup_parent(cgrp);
5462 	struct cgroup_subsys_state *css;
5463 	struct cgrp_cset_link *link;
5464 	int ssid;
5465 
5466 	lockdep_assert_held(&cgroup_mutex);
5467 
5468 	/*
5469 	 * Only migration can raise populated from zero and we're already
5470 	 * holding cgroup_mutex.
5471 	 */
5472 	if (cgroup_is_populated(cgrp))
5473 		return -EBUSY;
5474 
5475 	/*
5476 	 * Make sure there's no live children.  We can't test emptiness of
5477 	 * ->self.children as dead children linger on it while being
5478 	 * drained; otherwise, "rmdir parent/child parent" may fail.
5479 	 */
5480 	if (css_has_online_children(&cgrp->self))
5481 		return -EBUSY;
5482 
5483 	/*
5484 	 * Mark @cgrp and the associated csets dead.  The former prevents
5485 	 * further task migration and child creation by disabling
5486 	 * cgroup_lock_live_group().  The latter makes the csets ignored by
5487 	 * the migration path.
5488 	 */
5489 	cgrp->self.flags &= ~CSS_ONLINE;
5490 
5491 	spin_lock_irq(&css_set_lock);
5492 	list_for_each_entry(link, &cgrp->cset_links, cset_link)
5493 		link->cset->dead = true;
5494 	spin_unlock_irq(&css_set_lock);
5495 
5496 	/* initiate massacre of all css's */
5497 	for_each_css(css, ssid, cgrp)
5498 		kill_css(css);
5499 
5500 	/* clear and remove @cgrp dir, @cgrp has an extra ref on its kn */
5501 	css_clear_dir(&cgrp->self);
5502 	kernfs_remove(cgrp->kn);
5503 
5504 	if (parent && cgroup_is_threaded(cgrp))
5505 		parent->nr_threaded_children--;
5506 
5507 	spin_lock_irq(&css_set_lock);
5508 	for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) {
5509 		tcgrp->nr_descendants--;
5510 		tcgrp->nr_dying_descendants++;
5511 		/*
5512 		 * If the dying cgroup is frozen, decrease frozen descendants
5513 		 * counters of ancestor cgroups.
5514 		 */
5515 		if (test_bit(CGRP_FROZEN, &cgrp->flags))
5516 			tcgrp->freezer.nr_frozen_descendants--;
5517 	}
5518 	spin_unlock_irq(&css_set_lock);
5519 
5520 	cgroup1_check_for_release(parent);
5521 
5522 	/* put the base reference */
5523 	percpu_ref_kill(&cgrp->self.refcnt);
5524 
5525 	return 0;
5526 };
5527 
5528 int cgroup_rmdir(struct kernfs_node *kn)
5529 {
5530 	struct cgroup *cgrp;
5531 	int ret = 0;
5532 
5533 	cgrp = cgroup_kn_lock_live(kn, false);
5534 	if (!cgrp)
5535 		return 0;
5536 
5537 	ret = cgroup_destroy_locked(cgrp);
5538 	if (!ret)
5539 		TRACE_CGROUP_PATH(rmdir, cgrp);
5540 
5541 	cgroup_kn_unlock(kn);
5542 	return ret;
5543 }
5544 
5545 static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5546 	.show_options		= cgroup_show_options,
5547 	.mkdir			= cgroup_mkdir,
5548 	.rmdir			= cgroup_rmdir,
5549 	.show_path		= cgroup_show_path,
5550 };
5551 
5552 static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5553 {
5554 	struct cgroup_subsys_state *css;
5555 
5556 	pr_debug("Initializing cgroup subsys %s\n", ss->name);
5557 
5558 	mutex_lock(&cgroup_mutex);
5559 
5560 	idr_init(&ss->css_idr);
5561 	INIT_LIST_HEAD(&ss->cfts);
5562 
5563 	/* Create the root cgroup state for this subsystem */
5564 	ss->root = &cgrp_dfl_root;
5565 	css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5566 	/* We don't handle early failures gracefully */
5567 	BUG_ON(IS_ERR(css));
5568 	init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5569 
5570 	/*
5571 	 * Root csses are never destroyed and we can't initialize
5572 	 * percpu_ref during early init.  Disable refcnting.
5573 	 */
5574 	css->flags |= CSS_NO_REF;
5575 
5576 	if (early) {
5577 		/* allocation can't be done safely during early init */
5578 		css->id = 1;
5579 	} else {
5580 		css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5581 		BUG_ON(css->id < 0);
5582 	}
5583 
5584 	/* Update the init_css_set to contain a subsys
5585 	 * pointer to this state - since the subsystem is
5586 	 * newly registered, all tasks and hence the
5587 	 * init_css_set is in the subsystem's root cgroup. */
5588 	init_css_set.subsys[ss->id] = css;
5589 
5590 	have_fork_callback |= (bool)ss->fork << ss->id;
5591 	have_exit_callback |= (bool)ss->exit << ss->id;
5592 	have_release_callback |= (bool)ss->release << ss->id;
5593 	have_canfork_callback |= (bool)ss->can_fork << ss->id;
5594 
5595 	/* At system boot, before all subsystems have been
5596 	 * registered, no tasks have been forked, so we don't
5597 	 * need to invoke fork callbacks here. */
5598 	BUG_ON(!list_empty(&init_task.tasks));
5599 
5600 	BUG_ON(online_css(css));
5601 
5602 	mutex_unlock(&cgroup_mutex);
5603 }
5604 
5605 /**
5606  * cgroup_init_early - cgroup initialization at system boot
5607  *
5608  * Initialize cgroups at system boot, and initialize any
5609  * subsystems that request early init.
5610  */
5611 int __init cgroup_init_early(void)
5612 {
5613 	static struct cgroup_fs_context __initdata ctx;
5614 	struct cgroup_subsys *ss;
5615 	int i;
5616 
5617 	ctx.root = &cgrp_dfl_root;
5618 	init_cgroup_root(&ctx);
5619 	cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5620 
5621 	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5622 
5623 	for_each_subsys(ss, i) {
5624 		WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5625 		     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5626 		     i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5627 		     ss->id, ss->name);
5628 		WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5629 		     "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5630 
5631 		ss->id = i;
5632 		ss->name = cgroup_subsys_name[i];
5633 		if (!ss->legacy_name)
5634 			ss->legacy_name = cgroup_subsys_name[i];
5635 
5636 		if (ss->early_init)
5637 			cgroup_init_subsys(ss, true);
5638 	}
5639 	return 0;
5640 }
5641 
5642 static u16 cgroup_disable_mask __initdata;
5643 
5644 /**
5645  * cgroup_init - cgroup initialization
5646  *
5647  * Register cgroup filesystem and /proc file, and initialize
5648  * any subsystems that didn't request early init.
5649  */
5650 int __init cgroup_init(void)
5651 {
5652 	struct cgroup_subsys *ss;
5653 	int ssid;
5654 
5655 	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
5656 	BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
5657 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
5658 	BUG_ON(cgroup_init_cftypes(NULL, cgroup1_base_files));
5659 
5660 	cgroup_rstat_boot();
5661 
5662 	/*
5663 	 * The latency of the synchronize_rcu() is too high for cgroups,
5664 	 * avoid it at the cost of forcing all readers into the slow path.
5665 	 */
5666 	rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
5667 
5668 	get_user_ns(init_cgroup_ns.user_ns);
5669 
5670 	mutex_lock(&cgroup_mutex);
5671 
5672 	/*
5673 	 * Add init_css_set to the hash table so that dfl_root can link to
5674 	 * it during init.
5675 	 */
5676 	hash_add(css_set_table, &init_css_set.hlist,
5677 		 css_set_hash(init_css_set.subsys));
5678 
5679 	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5680 
5681 	mutex_unlock(&cgroup_mutex);
5682 
5683 	for_each_subsys(ss, ssid) {
5684 		if (ss->early_init) {
5685 			struct cgroup_subsys_state *css =
5686 				init_css_set.subsys[ss->id];
5687 
5688 			css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5689 						   GFP_KERNEL);
5690 			BUG_ON(css->id < 0);
5691 		} else {
5692 			cgroup_init_subsys(ss, false);
5693 		}
5694 
5695 		list_add_tail(&init_css_set.e_cset_node[ssid],
5696 			      &cgrp_dfl_root.cgrp.e_csets[ssid]);
5697 
5698 		/*
5699 		 * Setting dfl_root subsys_mask needs to consider the
5700 		 * disabled flag and cftype registration needs kmalloc,
5701 		 * both of which aren't available during early_init.
5702 		 */
5703 		if (cgroup_disable_mask & (1 << ssid)) {
5704 			static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5705 			printk(KERN_INFO "Disabling %s control group subsystem\n",
5706 			       ss->name);
5707 			continue;
5708 		}
5709 
5710 		if (cgroup1_ssid_disabled(ssid))
5711 			printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5712 			       ss->name);
5713 
5714 		cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5715 
5716 		/* implicit controllers must be threaded too */
5717 		WARN_ON(ss->implicit_on_dfl && !ss->threaded);
5718 
5719 		if (ss->implicit_on_dfl)
5720 			cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5721 		else if (!ss->dfl_cftypes)
5722 			cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5723 
5724 		if (ss->threaded)
5725 			cgrp_dfl_threaded_ss_mask |= 1 << ss->id;
5726 
5727 		if (ss->dfl_cftypes == ss->legacy_cftypes) {
5728 			WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5729 		} else {
5730 			WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5731 			WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5732 		}
5733 
5734 		if (ss->bind)
5735 			ss->bind(init_css_set.subsys[ssid]);
5736 
5737 		mutex_lock(&cgroup_mutex);
5738 		css_populate_dir(init_css_set.subsys[ssid]);
5739 		mutex_unlock(&cgroup_mutex);
5740 	}
5741 
5742 	/* init_css_set.subsys[] has been updated, re-hash */
5743 	hash_del(&init_css_set.hlist);
5744 	hash_add(css_set_table, &init_css_set.hlist,
5745 		 css_set_hash(init_css_set.subsys));
5746 
5747 	WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5748 	WARN_ON(register_filesystem(&cgroup_fs_type));
5749 	WARN_ON(register_filesystem(&cgroup2_fs_type));
5750 	WARN_ON(!proc_create_single("cgroups", 0, NULL, proc_cgroupstats_show));
5751 
5752 	return 0;
5753 }
5754 
5755 static int __init cgroup_wq_init(void)
5756 {
5757 	/*
5758 	 * There isn't much point in executing destruction path in
5759 	 * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5760 	 * Use 1 for @max_active.
5761 	 *
5762 	 * We would prefer to do this in cgroup_init() above, but that
5763 	 * is called before init_workqueues(): so leave this until after.
5764 	 */
5765 	cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5766 	BUG_ON(!cgroup_destroy_wq);
5767 	return 0;
5768 }
5769 core_initcall(cgroup_wq_init);
5770 
5771 void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
5772 					char *buf, size_t buflen)
5773 {
5774 	struct kernfs_node *kn;
5775 
5776 	kn = kernfs_get_node_by_id(cgrp_dfl_root.kf_root, id);
5777 	if (!kn)
5778 		return;
5779 	kernfs_path(kn, buf, buflen);
5780 	kernfs_put(kn);
5781 }
5782 
5783 /*
5784  * proc_cgroup_show()
5785  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5786  *  - Used for /proc/<pid>/cgroup.
5787  */
5788 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5789 		     struct pid *pid, struct task_struct *tsk)
5790 {
5791 	char *buf;
5792 	int retval;
5793 	struct cgroup_root *root;
5794 
5795 	retval = -ENOMEM;
5796 	buf = kmalloc(PATH_MAX, GFP_KERNEL);
5797 	if (!buf)
5798 		goto out;
5799 
5800 	mutex_lock(&cgroup_mutex);
5801 	spin_lock_irq(&css_set_lock);
5802 
5803 	for_each_root(root) {
5804 		struct cgroup_subsys *ss;
5805 		struct cgroup *cgrp;
5806 		int ssid, count = 0;
5807 
5808 		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5809 			continue;
5810 
5811 		seq_printf(m, "%d:", root->hierarchy_id);
5812 		if (root != &cgrp_dfl_root)
5813 			for_each_subsys(ss, ssid)
5814 				if (root->subsys_mask & (1 << ssid))
5815 					seq_printf(m, "%s%s", count++ ? "," : "",
5816 						   ss->legacy_name);
5817 		if (strlen(root->name))
5818 			seq_printf(m, "%sname=%s", count ? "," : "",
5819 				   root->name);
5820 		seq_putc(m, ':');
5821 
5822 		cgrp = task_cgroup_from_root(tsk, root);
5823 
5824 		/*
5825 		 * On traditional hierarchies, all zombie tasks show up as
5826 		 * belonging to the root cgroup.  On the default hierarchy,
5827 		 * while a zombie doesn't show up in "cgroup.procs" and
5828 		 * thus can't be migrated, its /proc/PID/cgroup keeps
5829 		 * reporting the cgroup it belonged to before exiting.  If
5830 		 * the cgroup is removed before the zombie is reaped,
5831 		 * " (deleted)" is appended to the cgroup path.
5832 		 */
5833 		if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5834 			retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5835 						current->nsproxy->cgroup_ns);
5836 			if (retval >= PATH_MAX)
5837 				retval = -ENAMETOOLONG;
5838 			if (retval < 0)
5839 				goto out_unlock;
5840 
5841 			seq_puts(m, buf);
5842 		} else {
5843 			seq_puts(m, "/");
5844 		}
5845 
5846 		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5847 			seq_puts(m, " (deleted)\n");
5848 		else
5849 			seq_putc(m, '\n');
5850 	}
5851 
5852 	retval = 0;
5853 out_unlock:
5854 	spin_unlock_irq(&css_set_lock);
5855 	mutex_unlock(&cgroup_mutex);
5856 	kfree(buf);
5857 out:
5858 	return retval;
5859 }
5860 
5861 /**
5862  * cgroup_fork - initialize cgroup related fields during copy_process()
5863  * @child: pointer to task_struct of forking parent process.
5864  *
5865  * A task is associated with the init_css_set until cgroup_post_fork()
5866  * attaches it to the parent's css_set.  Empty cg_list indicates that
5867  * @child isn't holding reference to its css_set.
5868  */
5869 void cgroup_fork(struct task_struct *child)
5870 {
5871 	RCU_INIT_POINTER(child->cgroups, &init_css_set);
5872 	INIT_LIST_HEAD(&child->cg_list);
5873 }
5874 
5875 /**
5876  * cgroup_can_fork - called on a new task before the process is exposed
5877  * @child: the task in question.
5878  *
5879  * This calls the subsystem can_fork() callbacks. If the can_fork() callback
5880  * returns an error, the fork aborts with that error code. This allows for
5881  * a cgroup subsystem to conditionally allow or deny new forks.
5882  */
5883 int cgroup_can_fork(struct task_struct *child)
5884 {
5885 	struct cgroup_subsys *ss;
5886 	int i, j, ret;
5887 
5888 	do_each_subsys_mask(ss, i, have_canfork_callback) {
5889 		ret = ss->can_fork(child);
5890 		if (ret)
5891 			goto out_revert;
5892 	} while_each_subsys_mask();
5893 
5894 	return 0;
5895 
5896 out_revert:
5897 	for_each_subsys(ss, j) {
5898 		if (j >= i)
5899 			break;
5900 		if (ss->cancel_fork)
5901 			ss->cancel_fork(child);
5902 	}
5903 
5904 	return ret;
5905 }
5906 
5907 /**
5908  * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5909  * @child: the task in question
5910  *
5911  * This calls the cancel_fork() callbacks if a fork failed *after*
5912  * cgroup_can_fork() succeded.
5913  */
5914 void cgroup_cancel_fork(struct task_struct *child)
5915 {
5916 	struct cgroup_subsys *ss;
5917 	int i;
5918 
5919 	for_each_subsys(ss, i)
5920 		if (ss->cancel_fork)
5921 			ss->cancel_fork(child);
5922 }
5923 
5924 /**
5925  * cgroup_post_fork - called on a new task after adding it to the task list
5926  * @child: the task in question
5927  *
5928  * Adds the task to the list running through its css_set if necessary and
5929  * call the subsystem fork() callbacks.  Has to be after the task is
5930  * visible on the task list in case we race with the first call to
5931  * cgroup_task_iter_start() - to guarantee that the new task ends up on its
5932  * list.
5933  */
5934 void cgroup_post_fork(struct task_struct *child)
5935 {
5936 	struct cgroup_subsys *ss;
5937 	int i;
5938 
5939 	/*
5940 	 * This may race against cgroup_enable_task_cg_lists().  As that
5941 	 * function sets use_task_css_set_links before grabbing
5942 	 * tasklist_lock and we just went through tasklist_lock to add
5943 	 * @child, it's guaranteed that either we see the set
5944 	 * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
5945 	 * @child during its iteration.
5946 	 *
5947 	 * If we won the race, @child is associated with %current's
5948 	 * css_set.  Grabbing css_set_lock guarantees both that the
5949 	 * association is stable, and, on completion of the parent's
5950 	 * migration, @child is visible in the source of migration or
5951 	 * already in the destination cgroup.  This guarantee is necessary
5952 	 * when implementing operations which need to migrate all tasks of
5953 	 * a cgroup to another.
5954 	 *
5955 	 * Note that if we lose to cgroup_enable_task_cg_lists(), @child
5956 	 * will remain in init_css_set.  This is safe because all tasks are
5957 	 * in the init_css_set before cg_links is enabled and there's no
5958 	 * operation which transfers all tasks out of init_css_set.
5959 	 */
5960 	if (use_task_css_set_links) {
5961 		struct css_set *cset;
5962 
5963 		spin_lock_irq(&css_set_lock);
5964 		cset = task_css_set(current);
5965 		if (list_empty(&child->cg_list)) {
5966 			get_css_set(cset);
5967 			cset->nr_tasks++;
5968 			css_set_move_task(child, NULL, cset, false);
5969 		}
5970 
5971 		/*
5972 		 * If the cgroup has to be frozen, the new task has too.
5973 		 * Let's set the JOBCTL_TRAP_FREEZE jobctl bit to get
5974 		 * the task into the frozen state.
5975 		 */
5976 		if (unlikely(cgroup_task_freeze(child))) {
5977 			spin_lock(&child->sighand->siglock);
5978 			WARN_ON_ONCE(child->frozen);
5979 			child->jobctl |= JOBCTL_TRAP_FREEZE;
5980 			spin_unlock(&child->sighand->siglock);
5981 
5982 			/*
5983 			 * Calling cgroup_update_frozen() isn't required here,
5984 			 * because it will be called anyway a bit later
5985 			 * from do_freezer_trap(). So we avoid cgroup's
5986 			 * transient switch from the frozen state and back.
5987 			 */
5988 		}
5989 
5990 		spin_unlock_irq(&css_set_lock);
5991 	}
5992 
5993 	/*
5994 	 * Call ss->fork().  This must happen after @child is linked on
5995 	 * css_set; otherwise, @child might change state between ->fork()
5996 	 * and addition to css_set.
5997 	 */
5998 	do_each_subsys_mask(ss, i, have_fork_callback) {
5999 		ss->fork(child);
6000 	} while_each_subsys_mask();
6001 }
6002 
6003 /**
6004  * cgroup_exit - detach cgroup from exiting task
6005  * @tsk: pointer to task_struct of exiting process
6006  *
6007  * Description: Detach cgroup from @tsk and release it.
6008  *
6009  * Note that cgroups marked notify_on_release force every task in
6010  * them to take the global cgroup_mutex mutex when exiting.
6011  * This could impact scaling on very large systems.  Be reluctant to
6012  * use notify_on_release cgroups where very high task exit scaling
6013  * is required on large systems.
6014  *
6015  * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
6016  * call cgroup_exit() while the task is still competent to handle
6017  * notify_on_release(), then leave the task attached to the root cgroup in
6018  * each hierarchy for the remainder of its exit.  No need to bother with
6019  * init_css_set refcnting.  init_css_set never goes away and we can't race
6020  * with migration path - PF_EXITING is visible to migration path.
6021  */
6022 void cgroup_exit(struct task_struct *tsk)
6023 {
6024 	struct cgroup_subsys *ss;
6025 	struct css_set *cset;
6026 	int i;
6027 
6028 	/*
6029 	 * Unlink from @tsk from its css_set.  As migration path can't race
6030 	 * with us, we can check css_set and cg_list without synchronization.
6031 	 */
6032 	cset = task_css_set(tsk);
6033 
6034 	if (!list_empty(&tsk->cg_list)) {
6035 		spin_lock_irq(&css_set_lock);
6036 		css_set_move_task(tsk, cset, NULL, false);
6037 		cset->nr_tasks--;
6038 
6039 		WARN_ON_ONCE(cgroup_task_frozen(tsk));
6040 		if (unlikely(cgroup_task_freeze(tsk)))
6041 			cgroup_update_frozen(task_dfl_cgroup(tsk));
6042 
6043 		spin_unlock_irq(&css_set_lock);
6044 	} else {
6045 		get_css_set(cset);
6046 	}
6047 
6048 	/* see cgroup_post_fork() for details */
6049 	do_each_subsys_mask(ss, i, have_exit_callback) {
6050 		ss->exit(tsk);
6051 	} while_each_subsys_mask();
6052 }
6053 
6054 void cgroup_release(struct task_struct *task)
6055 {
6056 	struct cgroup_subsys *ss;
6057 	int ssid;
6058 
6059 	do_each_subsys_mask(ss, ssid, have_release_callback) {
6060 		ss->release(task);
6061 	} while_each_subsys_mask();
6062 }
6063 
6064 void cgroup_free(struct task_struct *task)
6065 {
6066 	struct css_set *cset = task_css_set(task);
6067 	put_css_set(cset);
6068 }
6069 
6070 static int __init cgroup_disable(char *str)
6071 {
6072 	struct cgroup_subsys *ss;
6073 	char *token;
6074 	int i;
6075 
6076 	while ((token = strsep(&str, ",")) != NULL) {
6077 		if (!*token)
6078 			continue;
6079 
6080 		for_each_subsys(ss, i) {
6081 			if (strcmp(token, ss->name) &&
6082 			    strcmp(token, ss->legacy_name))
6083 				continue;
6084 			cgroup_disable_mask |= 1 << i;
6085 		}
6086 	}
6087 	return 1;
6088 }
6089 __setup("cgroup_disable=", cgroup_disable);
6090 
6091 void __init __weak enable_debug_cgroup(void) { }
6092 
6093 static int __init enable_cgroup_debug(char *str)
6094 {
6095 	cgroup_debug = true;
6096 	enable_debug_cgroup();
6097 	return 1;
6098 }
6099 __setup("cgroup_debug", enable_cgroup_debug);
6100 
6101 /**
6102  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
6103  * @dentry: directory dentry of interest
6104  * @ss: subsystem of interest
6105  *
6106  * If @dentry is a directory for a cgroup which has @ss enabled on it, try
6107  * to get the corresponding css and return it.  If such css doesn't exist
6108  * or can't be pinned, an ERR_PTR value is returned.
6109  */
6110 struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
6111 						       struct cgroup_subsys *ss)
6112 {
6113 	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
6114 	struct file_system_type *s_type = dentry->d_sb->s_type;
6115 	struct cgroup_subsys_state *css = NULL;
6116 	struct cgroup *cgrp;
6117 
6118 	/* is @dentry a cgroup dir? */
6119 	if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
6120 	    !kn || kernfs_type(kn) != KERNFS_DIR)
6121 		return ERR_PTR(-EBADF);
6122 
6123 	rcu_read_lock();
6124 
6125 	/*
6126 	 * This path doesn't originate from kernfs and @kn could already
6127 	 * have been or be removed at any point.  @kn->priv is RCU
6128 	 * protected for this access.  See css_release_work_fn() for details.
6129 	 */
6130 	cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
6131 	if (cgrp)
6132 		css = cgroup_css(cgrp, ss);
6133 
6134 	if (!css || !css_tryget_online(css))
6135 		css = ERR_PTR(-ENOENT);
6136 
6137 	rcu_read_unlock();
6138 	return css;
6139 }
6140 
6141 /**
6142  * css_from_id - lookup css by id
6143  * @id: the cgroup id
6144  * @ss: cgroup subsys to be looked into
6145  *
6146  * Returns the css if there's valid one with @id, otherwise returns NULL.
6147  * Should be called under rcu_read_lock().
6148  */
6149 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
6150 {
6151 	WARN_ON_ONCE(!rcu_read_lock_held());
6152 	return idr_find(&ss->css_idr, id);
6153 }
6154 
6155 /**
6156  * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
6157  * @path: path on the default hierarchy
6158  *
6159  * Find the cgroup at @path on the default hierarchy, increment its
6160  * reference count and return it.  Returns pointer to the found cgroup on
6161  * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
6162  * if @path points to a non-directory.
6163  */
6164 struct cgroup *cgroup_get_from_path(const char *path)
6165 {
6166 	struct kernfs_node *kn;
6167 	struct cgroup *cgrp;
6168 
6169 	mutex_lock(&cgroup_mutex);
6170 
6171 	kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
6172 	if (kn) {
6173 		if (kernfs_type(kn) == KERNFS_DIR) {
6174 			cgrp = kn->priv;
6175 			cgroup_get_live(cgrp);
6176 		} else {
6177 			cgrp = ERR_PTR(-ENOTDIR);
6178 		}
6179 		kernfs_put(kn);
6180 	} else {
6181 		cgrp = ERR_PTR(-ENOENT);
6182 	}
6183 
6184 	mutex_unlock(&cgroup_mutex);
6185 	return cgrp;
6186 }
6187 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
6188 
6189 /**
6190  * cgroup_get_from_fd - get a cgroup pointer from a fd
6191  * @fd: fd obtained by open(cgroup2_dir)
6192  *
6193  * Find the cgroup from a fd which should be obtained
6194  * by opening a cgroup directory.  Returns a pointer to the
6195  * cgroup on success. ERR_PTR is returned if the cgroup
6196  * cannot be found.
6197  */
6198 struct cgroup *cgroup_get_from_fd(int fd)
6199 {
6200 	struct cgroup_subsys_state *css;
6201 	struct cgroup *cgrp;
6202 	struct file *f;
6203 
6204 	f = fget_raw(fd);
6205 	if (!f)
6206 		return ERR_PTR(-EBADF);
6207 
6208 	css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
6209 	fput(f);
6210 	if (IS_ERR(css))
6211 		return ERR_CAST(css);
6212 
6213 	cgrp = css->cgroup;
6214 	if (!cgroup_on_dfl(cgrp)) {
6215 		cgroup_put(cgrp);
6216 		return ERR_PTR(-EBADF);
6217 	}
6218 
6219 	return cgrp;
6220 }
6221 EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
6222 
6223 /*
6224  * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
6225  * definition in cgroup-defs.h.
6226  */
6227 #ifdef CONFIG_SOCK_CGROUP_DATA
6228 
6229 #if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
6230 
6231 DEFINE_SPINLOCK(cgroup_sk_update_lock);
6232 static bool cgroup_sk_alloc_disabled __read_mostly;
6233 
6234 void cgroup_sk_alloc_disable(void)
6235 {
6236 	if (cgroup_sk_alloc_disabled)
6237 		return;
6238 	pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
6239 	cgroup_sk_alloc_disabled = true;
6240 }
6241 
6242 #else
6243 
6244 #define cgroup_sk_alloc_disabled	false
6245 
6246 #endif
6247 
6248 void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
6249 {
6250 	if (cgroup_sk_alloc_disabled)
6251 		return;
6252 
6253 	/* Socket clone path */
6254 	if (skcd->val) {
6255 		/*
6256 		 * We might be cloning a socket which is left in an empty
6257 		 * cgroup and the cgroup might have already been rmdir'd.
6258 		 * Don't use cgroup_get_live().
6259 		 */
6260 		cgroup_get(sock_cgroup_ptr(skcd));
6261 		return;
6262 	}
6263 
6264 	rcu_read_lock();
6265 
6266 	while (true) {
6267 		struct css_set *cset;
6268 
6269 		cset = task_css_set(current);
6270 		if (likely(cgroup_tryget(cset->dfl_cgrp))) {
6271 			skcd->val = (unsigned long)cset->dfl_cgrp;
6272 			break;
6273 		}
6274 		cpu_relax();
6275 	}
6276 
6277 	rcu_read_unlock();
6278 }
6279 
6280 void cgroup_sk_free(struct sock_cgroup_data *skcd)
6281 {
6282 	cgroup_put(sock_cgroup_ptr(skcd));
6283 }
6284 
6285 #endif	/* CONFIG_SOCK_CGROUP_DATA */
6286 
6287 #ifdef CONFIG_CGROUP_BPF
6288 int cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
6289 		      enum bpf_attach_type type, u32 flags)
6290 {
6291 	int ret;
6292 
6293 	mutex_lock(&cgroup_mutex);
6294 	ret = __cgroup_bpf_attach(cgrp, prog, type, flags);
6295 	mutex_unlock(&cgroup_mutex);
6296 	return ret;
6297 }
6298 int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
6299 		      enum bpf_attach_type type, u32 flags)
6300 {
6301 	int ret;
6302 
6303 	mutex_lock(&cgroup_mutex);
6304 	ret = __cgroup_bpf_detach(cgrp, prog, type);
6305 	mutex_unlock(&cgroup_mutex);
6306 	return ret;
6307 }
6308 int cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
6309 		     union bpf_attr __user *uattr)
6310 {
6311 	int ret;
6312 
6313 	mutex_lock(&cgroup_mutex);
6314 	ret = __cgroup_bpf_query(cgrp, attr, uattr);
6315 	mutex_unlock(&cgroup_mutex);
6316 	return ret;
6317 }
6318 #endif /* CONFIG_CGROUP_BPF */
6319 
6320 #ifdef CONFIG_SYSFS
6321 static ssize_t show_delegatable_files(struct cftype *files, char *buf,
6322 				      ssize_t size, const char *prefix)
6323 {
6324 	struct cftype *cft;
6325 	ssize_t ret = 0;
6326 
6327 	for (cft = files; cft && cft->name[0] != '\0'; cft++) {
6328 		if (!(cft->flags & CFTYPE_NS_DELEGATABLE))
6329 			continue;
6330 
6331 		if (prefix)
6332 			ret += snprintf(buf + ret, size - ret, "%s.", prefix);
6333 
6334 		ret += snprintf(buf + ret, size - ret, "%s\n", cft->name);
6335 
6336 		if (WARN_ON(ret >= size))
6337 			break;
6338 	}
6339 
6340 	return ret;
6341 }
6342 
6343 static ssize_t delegate_show(struct kobject *kobj, struct kobj_attribute *attr,
6344 			      char *buf)
6345 {
6346 	struct cgroup_subsys *ss;
6347 	int ssid;
6348 	ssize_t ret = 0;
6349 
6350 	ret = show_delegatable_files(cgroup_base_files, buf, PAGE_SIZE - ret,
6351 				     NULL);
6352 
6353 	for_each_subsys(ss, ssid)
6354 		ret += show_delegatable_files(ss->dfl_cftypes, buf + ret,
6355 					      PAGE_SIZE - ret,
6356 					      cgroup_subsys_name[ssid]);
6357 
6358 	return ret;
6359 }
6360 static struct kobj_attribute cgroup_delegate_attr = __ATTR_RO(delegate);
6361 
6362 static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr,
6363 			     char *buf)
6364 {
6365 	return snprintf(buf, PAGE_SIZE, "nsdelegate\nmemory_localevents\n");
6366 }
6367 static struct kobj_attribute cgroup_features_attr = __ATTR_RO(features);
6368 
6369 static struct attribute *cgroup_sysfs_attrs[] = {
6370 	&cgroup_delegate_attr.attr,
6371 	&cgroup_features_attr.attr,
6372 	NULL,
6373 };
6374 
6375 static const struct attribute_group cgroup_sysfs_attr_group = {
6376 	.attrs = cgroup_sysfs_attrs,
6377 	.name = "cgroup",
6378 };
6379 
6380 static int __init cgroup_sysfs_init(void)
6381 {
6382 	return sysfs_create_group(kernel_kobj, &cgroup_sysfs_attr_group);
6383 }
6384 subsys_initcall(cgroup_sysfs_init);
6385 #endif /* CONFIG_SYSFS */
6386