xref: /openbmc/linux/block/blk-cgroup.c (revision aaa746ad)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Common Block IO controller cgroup interface
4  *
5  * Based on ideas and code from CFQ, CFS and BFQ:
6  * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
7  *
8  * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
9  *		      Paolo Valente <paolo.valente@unimore.it>
10  *
11  * Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
12  * 	              Nauman Rafique <nauman@google.com>
13  *
14  * For policy-specific per-blkcg data:
15  * Copyright (C) 2015 Paolo Valente <paolo.valente@unimore.it>
16  *                    Arianna Avanzini <avanzini.arianna@gmail.com>
17  */
18 #include <linux/ioprio.h>
19 #include <linux/kdev_t.h>
20 #include <linux/module.h>
21 #include <linux/sched/signal.h>
22 #include <linux/err.h>
23 #include <linux/blkdev.h>
24 #include <linux/backing-dev.h>
25 #include <linux/slab.h>
26 #include <linux/delay.h>
27 #include <linux/atomic.h>
28 #include <linux/ctype.h>
29 #include <linux/resume_user_mode.h>
30 #include <linux/psi.h>
31 #include <linux/part_stat.h>
32 #include "blk.h"
33 #include "blk-cgroup.h"
34 #include "blk-ioprio.h"
35 #include "blk-throttle.h"
36 
37 /*
38  * blkcg_pol_mutex protects blkcg_policy[] and policy [de]activation.
39  * blkcg_pol_register_mutex nests outside of it and synchronizes entire
40  * policy [un]register operations including cgroup file additions /
41  * removals.  Putting cgroup file registration outside blkcg_pol_mutex
42  * allows grabbing it from cgroup callbacks.
43  */
44 static DEFINE_MUTEX(blkcg_pol_register_mutex);
45 static DEFINE_MUTEX(blkcg_pol_mutex);
46 
47 struct blkcg blkcg_root;
48 EXPORT_SYMBOL_GPL(blkcg_root);
49 
50 struct cgroup_subsys_state * const blkcg_root_css = &blkcg_root.css;
51 EXPORT_SYMBOL_GPL(blkcg_root_css);
52 
53 static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
54 
55 static LIST_HEAD(all_blkcgs);		/* protected by blkcg_pol_mutex */
56 
57 bool blkcg_debug_stats = false;
58 static struct workqueue_struct *blkcg_punt_bio_wq;
59 
60 #define BLKG_DESTROY_BATCH_SIZE  64
61 
62 /*
63  * Lockless lists for tracking IO stats update
64  *
65  * New IO stats are stored in the percpu iostat_cpu within blkcg_gq (blkg).
66  * There are multiple blkg's (one for each block device) attached to each
67  * blkcg. The rstat code keeps track of which cpu has IO stats updated,
68  * but it doesn't know which blkg has the updated stats. If there are many
69  * block devices in a system, the cost of iterating all the blkg's to flush
70  * out the IO stats can be high. To reduce such overhead, a set of percpu
71  * lockless lists (lhead) per blkcg are used to track the set of recently
72  * updated iostat_cpu's since the last flush. An iostat_cpu will be put
73  * onto the lockless list on the update side [blk_cgroup_bio_start()] if
74  * not there yet and then removed when being flushed [blkcg_rstat_flush()].
75  * References to blkg are gotten and then put back in the process to
76  * protect against blkg removal.
77  *
78  * Return: 0 if successful or -ENOMEM if allocation fails.
79  */
80 static int init_blkcg_llists(struct blkcg *blkcg)
81 {
82 	int cpu;
83 
84 	blkcg->lhead = alloc_percpu_gfp(struct llist_head, GFP_KERNEL);
85 	if (!blkcg->lhead)
86 		return -ENOMEM;
87 
88 	for_each_possible_cpu(cpu)
89 		init_llist_head(per_cpu_ptr(blkcg->lhead, cpu));
90 	return 0;
91 }
92 
93 /**
94  * blkcg_css - find the current css
95  *
96  * Find the css associated with either the kthread or the current task.
97  * This may return a dying css, so it is up to the caller to use tryget logic
98  * to confirm it is alive and well.
99  */
100 static struct cgroup_subsys_state *blkcg_css(void)
101 {
102 	struct cgroup_subsys_state *css;
103 
104 	css = kthread_blkcg();
105 	if (css)
106 		return css;
107 	return task_css(current, io_cgrp_id);
108 }
109 
110 static bool blkcg_policy_enabled(struct request_queue *q,
111 				 const struct blkcg_policy *pol)
112 {
113 	return pol && test_bit(pol->plid, q->blkcg_pols);
114 }
115 
116 static void blkg_free_workfn(struct work_struct *work)
117 {
118 	struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
119 					     free_work);
120 	int i;
121 
122 	for (i = 0; i < BLKCG_MAX_POLS; i++)
123 		if (blkg->pd[i])
124 			blkcg_policy[i]->pd_free_fn(blkg->pd[i]);
125 
126 	if (blkg->q)
127 		blk_put_queue(blkg->q);
128 	free_percpu(blkg->iostat_cpu);
129 	percpu_ref_exit(&blkg->refcnt);
130 	kfree(blkg);
131 }
132 
133 /**
134  * blkg_free - free a blkg
135  * @blkg: blkg to free
136  *
137  * Free @blkg which may be partially allocated.
138  */
139 static void blkg_free(struct blkcg_gq *blkg)
140 {
141 	if (!blkg)
142 		return;
143 
144 	/*
145 	 * Both ->pd_free_fn() and request queue's release handler may
146 	 * sleep, so free us by scheduling one work func
147 	 */
148 	INIT_WORK(&blkg->free_work, blkg_free_workfn);
149 	schedule_work(&blkg->free_work);
150 }
151 
152 static void __blkg_release(struct rcu_head *rcu)
153 {
154 	struct blkcg_gq *blkg = container_of(rcu, struct blkcg_gq, rcu_head);
155 
156 	WARN_ON(!bio_list_empty(&blkg->async_bios));
157 
158 	/* release the blkcg and parent blkg refs this blkg has been holding */
159 	css_put(&blkg->blkcg->css);
160 	if (blkg->parent)
161 		blkg_put(blkg->parent);
162 	blkg_free(blkg);
163 }
164 
165 /*
166  * A group is RCU protected, but having an rcu lock does not mean that one
167  * can access all the fields of blkg and assume these are valid.  For
168  * example, don't try to follow throtl_data and request queue links.
169  *
170  * Having a reference to blkg under an rcu allows accesses to only values
171  * local to groups like group stats and group rate limits.
172  */
173 static void blkg_release(struct percpu_ref *ref)
174 {
175 	struct blkcg_gq *blkg = container_of(ref, struct blkcg_gq, refcnt);
176 
177 	call_rcu(&blkg->rcu_head, __blkg_release);
178 }
179 
180 static void blkg_async_bio_workfn(struct work_struct *work)
181 {
182 	struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
183 					     async_bio_work);
184 	struct bio_list bios = BIO_EMPTY_LIST;
185 	struct bio *bio;
186 	struct blk_plug plug;
187 	bool need_plug = false;
188 
189 	/* as long as there are pending bios, @blkg can't go away */
190 	spin_lock_bh(&blkg->async_bio_lock);
191 	bio_list_merge(&bios, &blkg->async_bios);
192 	bio_list_init(&blkg->async_bios);
193 	spin_unlock_bh(&blkg->async_bio_lock);
194 
195 	/* start plug only when bio_list contains at least 2 bios */
196 	if (bios.head && bios.head->bi_next) {
197 		need_plug = true;
198 		blk_start_plug(&plug);
199 	}
200 	while ((bio = bio_list_pop(&bios)))
201 		submit_bio(bio);
202 	if (need_plug)
203 		blk_finish_plug(&plug);
204 }
205 
206 /**
207  * bio_blkcg_css - return the blkcg CSS associated with a bio
208  * @bio: target bio
209  *
210  * This returns the CSS for the blkcg associated with a bio, or %NULL if not
211  * associated. Callers are expected to either handle %NULL or know association
212  * has been done prior to calling this.
213  */
214 struct cgroup_subsys_state *bio_blkcg_css(struct bio *bio)
215 {
216 	if (!bio || !bio->bi_blkg)
217 		return NULL;
218 	return &bio->bi_blkg->blkcg->css;
219 }
220 EXPORT_SYMBOL_GPL(bio_blkcg_css);
221 
222 /**
223  * blkcg_parent - get the parent of a blkcg
224  * @blkcg: blkcg of interest
225  *
226  * Return the parent blkcg of @blkcg.  Can be called anytime.
227  */
228 static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
229 {
230 	return css_to_blkcg(blkcg->css.parent);
231 }
232 
233 /**
234  * blkg_alloc - allocate a blkg
235  * @blkcg: block cgroup the new blkg is associated with
236  * @disk: gendisk the new blkg is associated with
237  * @gfp_mask: allocation mask to use
238  *
239  * Allocate a new blkg assocating @blkcg and @q.
240  */
241 static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk,
242 				   gfp_t gfp_mask)
243 {
244 	struct blkcg_gq *blkg;
245 	int i, cpu;
246 
247 	/* alloc and init base part */
248 	blkg = kzalloc_node(sizeof(*blkg), gfp_mask, disk->queue->node);
249 	if (!blkg)
250 		return NULL;
251 
252 	if (percpu_ref_init(&blkg->refcnt, blkg_release, 0, gfp_mask))
253 		goto err_free;
254 
255 	blkg->iostat_cpu = alloc_percpu_gfp(struct blkg_iostat_set, gfp_mask);
256 	if (!blkg->iostat_cpu)
257 		goto err_free;
258 
259 	if (!blk_get_queue(disk->queue))
260 		goto err_free;
261 
262 	blkg->q = disk->queue;
263 	INIT_LIST_HEAD(&blkg->q_node);
264 	spin_lock_init(&blkg->async_bio_lock);
265 	bio_list_init(&blkg->async_bios);
266 	INIT_WORK(&blkg->async_bio_work, blkg_async_bio_workfn);
267 	blkg->blkcg = blkcg;
268 
269 	u64_stats_init(&blkg->iostat.sync);
270 	for_each_possible_cpu(cpu) {
271 		u64_stats_init(&per_cpu_ptr(blkg->iostat_cpu, cpu)->sync);
272 		per_cpu_ptr(blkg->iostat_cpu, cpu)->blkg = blkg;
273 	}
274 
275 	for (i = 0; i < BLKCG_MAX_POLS; i++) {
276 		struct blkcg_policy *pol = blkcg_policy[i];
277 		struct blkg_policy_data *pd;
278 
279 		if (!blkcg_policy_enabled(disk->queue, pol))
280 			continue;
281 
282 		/* alloc per-policy data and attach it to blkg */
283 		pd = pol->pd_alloc_fn(gfp_mask, disk->queue, blkcg);
284 		if (!pd)
285 			goto err_free;
286 
287 		blkg->pd[i] = pd;
288 		pd->blkg = blkg;
289 		pd->plid = i;
290 	}
291 
292 	return blkg;
293 
294 err_free:
295 	blkg_free(blkg);
296 	return NULL;
297 }
298 
299 /*
300  * If @new_blkg is %NULL, this function tries to allocate a new one as
301  * necessary using %GFP_NOWAIT.  @new_blkg is always consumed on return.
302  */
303 static struct blkcg_gq *blkg_create(struct blkcg *blkcg, struct gendisk *disk,
304 				    struct blkcg_gq *new_blkg)
305 {
306 	struct blkcg_gq *blkg;
307 	int i, ret;
308 
309 	lockdep_assert_held(&disk->queue->queue_lock);
310 
311 	/* request_queue is dying, do not create/recreate a blkg */
312 	if (blk_queue_dying(disk->queue)) {
313 		ret = -ENODEV;
314 		goto err_free_blkg;
315 	}
316 
317 	/* blkg holds a reference to blkcg */
318 	if (!css_tryget_online(&blkcg->css)) {
319 		ret = -ENODEV;
320 		goto err_free_blkg;
321 	}
322 
323 	/* allocate */
324 	if (!new_blkg) {
325 		new_blkg = blkg_alloc(blkcg, disk, GFP_NOWAIT | __GFP_NOWARN);
326 		if (unlikely(!new_blkg)) {
327 			ret = -ENOMEM;
328 			goto err_put_css;
329 		}
330 	}
331 	blkg = new_blkg;
332 
333 	/* link parent */
334 	if (blkcg_parent(blkcg)) {
335 		blkg->parent = blkg_lookup(blkcg_parent(blkcg), disk->queue);
336 		if (WARN_ON_ONCE(!blkg->parent)) {
337 			ret = -ENODEV;
338 			goto err_put_css;
339 		}
340 		blkg_get(blkg->parent);
341 	}
342 
343 	/* invoke per-policy init */
344 	for (i = 0; i < BLKCG_MAX_POLS; i++) {
345 		struct blkcg_policy *pol = blkcg_policy[i];
346 
347 		if (blkg->pd[i] && pol->pd_init_fn)
348 			pol->pd_init_fn(blkg->pd[i]);
349 	}
350 
351 	/* insert */
352 	spin_lock(&blkcg->lock);
353 	ret = radix_tree_insert(&blkcg->blkg_tree, disk->queue->id, blkg);
354 	if (likely(!ret)) {
355 		hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
356 		list_add(&blkg->q_node, &disk->queue->blkg_list);
357 
358 		for (i = 0; i < BLKCG_MAX_POLS; i++) {
359 			struct blkcg_policy *pol = blkcg_policy[i];
360 
361 			if (blkg->pd[i] && pol->pd_online_fn)
362 				pol->pd_online_fn(blkg->pd[i]);
363 		}
364 	}
365 	blkg->online = true;
366 	spin_unlock(&blkcg->lock);
367 
368 	if (!ret)
369 		return blkg;
370 
371 	/* @blkg failed fully initialized, use the usual release path */
372 	blkg_put(blkg);
373 	return ERR_PTR(ret);
374 
375 err_put_css:
376 	css_put(&blkcg->css);
377 err_free_blkg:
378 	blkg_free(new_blkg);
379 	return ERR_PTR(ret);
380 }
381 
382 /**
383  * blkg_lookup_create - lookup blkg, try to create one if not there
384  * @blkcg: blkcg of interest
385  * @disk: gendisk of interest
386  *
387  * Lookup blkg for the @blkcg - @disk pair.  If it doesn't exist, try to
388  * create one.  blkg creation is performed recursively from blkcg_root such
389  * that all non-root blkg's have access to the parent blkg.  This function
390  * should be called under RCU read lock and takes @disk->queue->queue_lock.
391  *
392  * Returns the blkg or the closest blkg if blkg_create() fails as it walks
393  * down from root.
394  */
395 static struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
396 		struct gendisk *disk)
397 {
398 	struct request_queue *q = disk->queue;
399 	struct blkcg_gq *blkg;
400 	unsigned long flags;
401 
402 	WARN_ON_ONCE(!rcu_read_lock_held());
403 
404 	blkg = blkg_lookup(blkcg, q);
405 	if (blkg)
406 		return blkg;
407 
408 	spin_lock_irqsave(&q->queue_lock, flags);
409 	blkg = blkg_lookup(blkcg, q);
410 	if (blkg) {
411 		if (blkcg != &blkcg_root &&
412 		    blkg != rcu_dereference(blkcg->blkg_hint))
413 			rcu_assign_pointer(blkcg->blkg_hint, blkg);
414 		goto found;
415 	}
416 
417 	/*
418 	 * Create blkgs walking down from blkcg_root to @blkcg, so that all
419 	 * non-root blkgs have access to their parents.  Returns the closest
420 	 * blkg to the intended blkg should blkg_create() fail.
421 	 */
422 	while (true) {
423 		struct blkcg *pos = blkcg;
424 		struct blkcg *parent = blkcg_parent(blkcg);
425 		struct blkcg_gq *ret_blkg = q->root_blkg;
426 
427 		while (parent) {
428 			blkg = blkg_lookup(parent, q);
429 			if (blkg) {
430 				/* remember closest blkg */
431 				ret_blkg = blkg;
432 				break;
433 			}
434 			pos = parent;
435 			parent = blkcg_parent(parent);
436 		}
437 
438 		blkg = blkg_create(pos, disk, NULL);
439 		if (IS_ERR(blkg)) {
440 			blkg = ret_blkg;
441 			break;
442 		}
443 		if (pos == blkcg)
444 			break;
445 	}
446 
447 found:
448 	spin_unlock_irqrestore(&q->queue_lock, flags);
449 	return blkg;
450 }
451 
452 static void blkg_destroy(struct blkcg_gq *blkg)
453 {
454 	struct blkcg *blkcg = blkg->blkcg;
455 	int i;
456 
457 	lockdep_assert_held(&blkg->q->queue_lock);
458 	lockdep_assert_held(&blkcg->lock);
459 
460 	/* Something wrong if we are trying to remove same group twice */
461 	WARN_ON_ONCE(list_empty(&blkg->q_node));
462 	WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
463 
464 	for (i = 0; i < BLKCG_MAX_POLS; i++) {
465 		struct blkcg_policy *pol = blkcg_policy[i];
466 
467 		if (blkg->pd[i] && pol->pd_offline_fn)
468 			pol->pd_offline_fn(blkg->pd[i]);
469 	}
470 
471 	blkg->online = false;
472 
473 	radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
474 	list_del_init(&blkg->q_node);
475 	hlist_del_init_rcu(&blkg->blkcg_node);
476 
477 	/*
478 	 * Both setting lookup hint to and clearing it from @blkg are done
479 	 * under queue_lock.  If it's not pointing to @blkg now, it never
480 	 * will.  Hint assignment itself can race safely.
481 	 */
482 	if (rcu_access_pointer(blkcg->blkg_hint) == blkg)
483 		rcu_assign_pointer(blkcg->blkg_hint, NULL);
484 
485 	/*
486 	 * Put the reference taken at the time of creation so that when all
487 	 * queues are gone, group can be destroyed.
488 	 */
489 	percpu_ref_kill(&blkg->refcnt);
490 }
491 
492 static void blkg_destroy_all(struct gendisk *disk)
493 {
494 	struct request_queue *q = disk->queue;
495 	struct blkcg_gq *blkg, *n;
496 	int count = BLKG_DESTROY_BATCH_SIZE;
497 
498 restart:
499 	spin_lock_irq(&q->queue_lock);
500 	list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
501 		struct blkcg *blkcg = blkg->blkcg;
502 
503 		spin_lock(&blkcg->lock);
504 		blkg_destroy(blkg);
505 		spin_unlock(&blkcg->lock);
506 
507 		/*
508 		 * in order to avoid holding the spin lock for too long, release
509 		 * it when a batch of blkgs are destroyed.
510 		 */
511 		if (!(--count)) {
512 			count = BLKG_DESTROY_BATCH_SIZE;
513 			spin_unlock_irq(&q->queue_lock);
514 			cond_resched();
515 			goto restart;
516 		}
517 	}
518 
519 	q->root_blkg = NULL;
520 	spin_unlock_irq(&q->queue_lock);
521 }
522 
523 static int blkcg_reset_stats(struct cgroup_subsys_state *css,
524 			     struct cftype *cftype, u64 val)
525 {
526 	struct blkcg *blkcg = css_to_blkcg(css);
527 	struct blkcg_gq *blkg;
528 	int i, cpu;
529 
530 	mutex_lock(&blkcg_pol_mutex);
531 	spin_lock_irq(&blkcg->lock);
532 
533 	/*
534 	 * Note that stat reset is racy - it doesn't synchronize against
535 	 * stat updates.  This is a debug feature which shouldn't exist
536 	 * anyway.  If you get hit by a race, retry.
537 	 */
538 	hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
539 		for_each_possible_cpu(cpu) {
540 			struct blkg_iostat_set *bis =
541 				per_cpu_ptr(blkg->iostat_cpu, cpu);
542 			memset(bis, 0, sizeof(*bis));
543 		}
544 		memset(&blkg->iostat, 0, sizeof(blkg->iostat));
545 
546 		for (i = 0; i < BLKCG_MAX_POLS; i++) {
547 			struct blkcg_policy *pol = blkcg_policy[i];
548 
549 			if (blkg->pd[i] && pol->pd_reset_stats_fn)
550 				pol->pd_reset_stats_fn(blkg->pd[i]);
551 		}
552 	}
553 
554 	spin_unlock_irq(&blkcg->lock);
555 	mutex_unlock(&blkcg_pol_mutex);
556 	return 0;
557 }
558 
559 const char *blkg_dev_name(struct blkcg_gq *blkg)
560 {
561 	if (!blkg->q->disk || !blkg->q->disk->bdi->dev)
562 		return NULL;
563 	return bdi_dev_name(blkg->q->disk->bdi);
564 }
565 
566 /**
567  * blkcg_print_blkgs - helper for printing per-blkg data
568  * @sf: seq_file to print to
569  * @blkcg: blkcg of interest
570  * @prfill: fill function to print out a blkg
571  * @pol: policy in question
572  * @data: data to be passed to @prfill
573  * @show_total: to print out sum of prfill return values or not
574  *
575  * This function invokes @prfill on each blkg of @blkcg if pd for the
576  * policy specified by @pol exists.  @prfill is invoked with @sf, the
577  * policy data and @data and the matching queue lock held.  If @show_total
578  * is %true, the sum of the return values from @prfill is printed with
579  * "Total" label at the end.
580  *
581  * This is to be used to construct print functions for
582  * cftype->read_seq_string method.
583  */
584 void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
585 		       u64 (*prfill)(struct seq_file *,
586 				     struct blkg_policy_data *, int),
587 		       const struct blkcg_policy *pol, int data,
588 		       bool show_total)
589 {
590 	struct blkcg_gq *blkg;
591 	u64 total = 0;
592 
593 	rcu_read_lock();
594 	hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
595 		spin_lock_irq(&blkg->q->queue_lock);
596 		if (blkcg_policy_enabled(blkg->q, pol))
597 			total += prfill(sf, blkg->pd[pol->plid], data);
598 		spin_unlock_irq(&blkg->q->queue_lock);
599 	}
600 	rcu_read_unlock();
601 
602 	if (show_total)
603 		seq_printf(sf, "Total %llu\n", (unsigned long long)total);
604 }
605 EXPORT_SYMBOL_GPL(blkcg_print_blkgs);
606 
607 /**
608  * __blkg_prfill_u64 - prfill helper for a single u64 value
609  * @sf: seq_file to print to
610  * @pd: policy private data of interest
611  * @v: value to print
612  *
613  * Print @v to @sf for the device associated with @pd.
614  */
615 u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v)
616 {
617 	const char *dname = blkg_dev_name(pd->blkg);
618 
619 	if (!dname)
620 		return 0;
621 
622 	seq_printf(sf, "%s %llu\n", dname, (unsigned long long)v);
623 	return v;
624 }
625 EXPORT_SYMBOL_GPL(__blkg_prfill_u64);
626 
627 /**
628  * blkcg_conf_open_bdev - parse and open bdev for per-blkg config update
629  * @inputp: input string pointer
630  *
631  * Parse the device node prefix part, MAJ:MIN, of per-blkg config update
632  * from @input and get and return the matching bdev.  *@inputp is
633  * updated to point past the device node prefix.  Returns an ERR_PTR()
634  * value on error.
635  *
636  * Use this function iff blkg_conf_prep() can't be used for some reason.
637  */
638 struct block_device *blkcg_conf_open_bdev(char **inputp)
639 {
640 	char *input = *inputp;
641 	unsigned int major, minor;
642 	struct block_device *bdev;
643 	int key_len;
644 
645 	if (sscanf(input, "%u:%u%n", &major, &minor, &key_len) != 2)
646 		return ERR_PTR(-EINVAL);
647 
648 	input += key_len;
649 	if (!isspace(*input))
650 		return ERR_PTR(-EINVAL);
651 	input = skip_spaces(input);
652 
653 	bdev = blkdev_get_no_open(MKDEV(major, minor));
654 	if (!bdev)
655 		return ERR_PTR(-ENODEV);
656 	if (bdev_is_partition(bdev)) {
657 		blkdev_put_no_open(bdev);
658 		return ERR_PTR(-ENODEV);
659 	}
660 
661 	*inputp = input;
662 	return bdev;
663 }
664 
665 /**
666  * blkg_conf_prep - parse and prepare for per-blkg config update
667  * @blkcg: target block cgroup
668  * @pol: target policy
669  * @input: input string
670  * @ctx: blkg_conf_ctx to be filled
671  *
672  * Parse per-blkg config update from @input and initialize @ctx with the
673  * result.  @ctx->blkg points to the blkg to be updated and @ctx->body the
674  * part of @input following MAJ:MIN.  This function returns with RCU read
675  * lock and queue lock held and must be paired with blkg_conf_finish().
676  */
677 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
678 		   char *input, struct blkg_conf_ctx *ctx)
679 	__acquires(rcu) __acquires(&bdev->bd_queue->queue_lock)
680 {
681 	struct block_device *bdev;
682 	struct gendisk *disk;
683 	struct request_queue *q;
684 	struct blkcg_gq *blkg;
685 	int ret;
686 
687 	bdev = blkcg_conf_open_bdev(&input);
688 	if (IS_ERR(bdev))
689 		return PTR_ERR(bdev);
690 	disk = bdev->bd_disk;
691 	q = disk->queue;
692 
693 	/*
694 	 * blkcg_deactivate_policy() requires queue to be frozen, we can grab
695 	 * q_usage_counter to prevent concurrent with blkcg_deactivate_policy().
696 	 */
697 	ret = blk_queue_enter(q, 0);
698 	if (ret)
699 		goto fail;
700 
701 	rcu_read_lock();
702 	spin_lock_irq(&q->queue_lock);
703 
704 	if (!blkcg_policy_enabled(q, pol)) {
705 		ret = -EOPNOTSUPP;
706 		goto fail_unlock;
707 	}
708 
709 	blkg = blkg_lookup(blkcg, q);
710 	if (blkg)
711 		goto success;
712 
713 	/*
714 	 * Create blkgs walking down from blkcg_root to @blkcg, so that all
715 	 * non-root blkgs have access to their parents.
716 	 */
717 	while (true) {
718 		struct blkcg *pos = blkcg;
719 		struct blkcg *parent;
720 		struct blkcg_gq *new_blkg;
721 
722 		parent = blkcg_parent(blkcg);
723 		while (parent && !blkg_lookup(parent, q)) {
724 			pos = parent;
725 			parent = blkcg_parent(parent);
726 		}
727 
728 		/* Drop locks to do new blkg allocation with GFP_KERNEL. */
729 		spin_unlock_irq(&q->queue_lock);
730 		rcu_read_unlock();
731 
732 		new_blkg = blkg_alloc(pos, disk, GFP_KERNEL);
733 		if (unlikely(!new_blkg)) {
734 			ret = -ENOMEM;
735 			goto fail_exit_queue;
736 		}
737 
738 		if (radix_tree_preload(GFP_KERNEL)) {
739 			blkg_free(new_blkg);
740 			ret = -ENOMEM;
741 			goto fail_exit_queue;
742 		}
743 
744 		rcu_read_lock();
745 		spin_lock_irq(&q->queue_lock);
746 
747 		if (!blkcg_policy_enabled(q, pol)) {
748 			blkg_free(new_blkg);
749 			ret = -EOPNOTSUPP;
750 			goto fail_preloaded;
751 		}
752 
753 		blkg = blkg_lookup(pos, q);
754 		if (blkg) {
755 			blkg_free(new_blkg);
756 		} else {
757 			blkg = blkg_create(pos, disk, new_blkg);
758 			if (IS_ERR(blkg)) {
759 				ret = PTR_ERR(blkg);
760 				goto fail_preloaded;
761 			}
762 		}
763 
764 		radix_tree_preload_end();
765 
766 		if (pos == blkcg)
767 			goto success;
768 	}
769 success:
770 	blk_queue_exit(q);
771 	ctx->bdev = bdev;
772 	ctx->blkg = blkg;
773 	ctx->body = input;
774 	return 0;
775 
776 fail_preloaded:
777 	radix_tree_preload_end();
778 fail_unlock:
779 	spin_unlock_irq(&q->queue_lock);
780 	rcu_read_unlock();
781 fail_exit_queue:
782 	blk_queue_exit(q);
783 fail:
784 	blkdev_put_no_open(bdev);
785 	/*
786 	 * If queue was bypassing, we should retry.  Do so after a
787 	 * short msleep().  It isn't strictly necessary but queue
788 	 * can be bypassing for some time and it's always nice to
789 	 * avoid busy looping.
790 	 */
791 	if (ret == -EBUSY) {
792 		msleep(10);
793 		ret = restart_syscall();
794 	}
795 	return ret;
796 }
797 EXPORT_SYMBOL_GPL(blkg_conf_prep);
798 
799 /**
800  * blkg_conf_finish - finish up per-blkg config update
801  * @ctx: blkg_conf_ctx initialized by blkg_conf_prep()
802  *
803  * Finish up after per-blkg config update.  This function must be paired
804  * with blkg_conf_prep().
805  */
806 void blkg_conf_finish(struct blkg_conf_ctx *ctx)
807 	__releases(&ctx->bdev->bd_queue->queue_lock) __releases(rcu)
808 {
809 	spin_unlock_irq(&bdev_get_queue(ctx->bdev)->queue_lock);
810 	rcu_read_unlock();
811 	blkdev_put_no_open(ctx->bdev);
812 }
813 EXPORT_SYMBOL_GPL(blkg_conf_finish);
814 
815 static void blkg_iostat_set(struct blkg_iostat *dst, struct blkg_iostat *src)
816 {
817 	int i;
818 
819 	for (i = 0; i < BLKG_IOSTAT_NR; i++) {
820 		dst->bytes[i] = src->bytes[i];
821 		dst->ios[i] = src->ios[i];
822 	}
823 }
824 
825 static void blkg_iostat_add(struct blkg_iostat *dst, struct blkg_iostat *src)
826 {
827 	int i;
828 
829 	for (i = 0; i < BLKG_IOSTAT_NR; i++) {
830 		dst->bytes[i] += src->bytes[i];
831 		dst->ios[i] += src->ios[i];
832 	}
833 }
834 
835 static void blkg_iostat_sub(struct blkg_iostat *dst, struct blkg_iostat *src)
836 {
837 	int i;
838 
839 	for (i = 0; i < BLKG_IOSTAT_NR; i++) {
840 		dst->bytes[i] -= src->bytes[i];
841 		dst->ios[i] -= src->ios[i];
842 	}
843 }
844 
845 static void blkcg_iostat_update(struct blkcg_gq *blkg, struct blkg_iostat *cur,
846 				struct blkg_iostat *last)
847 {
848 	struct blkg_iostat delta;
849 	unsigned long flags;
850 
851 	/* propagate percpu delta to global */
852 	flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
853 	blkg_iostat_set(&delta, cur);
854 	blkg_iostat_sub(&delta, last);
855 	blkg_iostat_add(&blkg->iostat.cur, &delta);
856 	blkg_iostat_add(last, &delta);
857 	u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
858 }
859 
860 static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu)
861 {
862 	struct blkcg *blkcg = css_to_blkcg(css);
863 	struct llist_head *lhead = per_cpu_ptr(blkcg->lhead, cpu);
864 	struct llist_node *lnode;
865 	struct blkg_iostat_set *bisc, *next_bisc;
866 
867 	/* Root-level stats are sourced from system-wide IO stats */
868 	if (!cgroup_parent(css->cgroup))
869 		return;
870 
871 	rcu_read_lock();
872 
873 	lnode = llist_del_all(lhead);
874 	if (!lnode)
875 		goto out;
876 
877 	/*
878 	 * Iterate only the iostat_cpu's queued in the lockless list.
879 	 */
880 	llist_for_each_entry_safe(bisc, next_bisc, lnode, lnode) {
881 		struct blkcg_gq *blkg = bisc->blkg;
882 		struct blkcg_gq *parent = blkg->parent;
883 		struct blkg_iostat cur;
884 		unsigned int seq;
885 
886 		WRITE_ONCE(bisc->lqueued, false);
887 
888 		/* fetch the current per-cpu values */
889 		do {
890 			seq = u64_stats_fetch_begin(&bisc->sync);
891 			blkg_iostat_set(&cur, &bisc->cur);
892 		} while (u64_stats_fetch_retry(&bisc->sync, seq));
893 
894 		blkcg_iostat_update(blkg, &cur, &bisc->last);
895 
896 		/* propagate global delta to parent (unless that's root) */
897 		if (parent && parent->parent)
898 			blkcg_iostat_update(parent, &blkg->iostat.cur,
899 					    &blkg->iostat.last);
900 		percpu_ref_put(&blkg->refcnt);
901 	}
902 
903 out:
904 	rcu_read_unlock();
905 }
906 
907 /*
908  * We source root cgroup stats from the system-wide stats to avoid
909  * tracking the same information twice and incurring overhead when no
910  * cgroups are defined. For that reason, cgroup_rstat_flush in
911  * blkcg_print_stat does not actually fill out the iostat in the root
912  * cgroup's blkcg_gq.
913  *
914  * However, we would like to re-use the printing code between the root and
915  * non-root cgroups to the extent possible. For that reason, we simulate
916  * flushing the root cgroup's stats by explicitly filling in the iostat
917  * with disk level statistics.
918  */
919 static void blkcg_fill_root_iostats(void)
920 {
921 	struct class_dev_iter iter;
922 	struct device *dev;
923 
924 	class_dev_iter_init(&iter, &block_class, NULL, &disk_type);
925 	while ((dev = class_dev_iter_next(&iter))) {
926 		struct block_device *bdev = dev_to_bdev(dev);
927 		struct blkcg_gq *blkg = bdev->bd_disk->queue->root_blkg;
928 		struct blkg_iostat tmp;
929 		int cpu;
930 		unsigned long flags;
931 
932 		memset(&tmp, 0, sizeof(tmp));
933 		for_each_possible_cpu(cpu) {
934 			struct disk_stats *cpu_dkstats;
935 
936 			cpu_dkstats = per_cpu_ptr(bdev->bd_stats, cpu);
937 			tmp.ios[BLKG_IOSTAT_READ] +=
938 				cpu_dkstats->ios[STAT_READ];
939 			tmp.ios[BLKG_IOSTAT_WRITE] +=
940 				cpu_dkstats->ios[STAT_WRITE];
941 			tmp.ios[BLKG_IOSTAT_DISCARD] +=
942 				cpu_dkstats->ios[STAT_DISCARD];
943 			// convert sectors to bytes
944 			tmp.bytes[BLKG_IOSTAT_READ] +=
945 				cpu_dkstats->sectors[STAT_READ] << 9;
946 			tmp.bytes[BLKG_IOSTAT_WRITE] +=
947 				cpu_dkstats->sectors[STAT_WRITE] << 9;
948 			tmp.bytes[BLKG_IOSTAT_DISCARD] +=
949 				cpu_dkstats->sectors[STAT_DISCARD] << 9;
950 		}
951 
952 		flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
953 		blkg_iostat_set(&blkg->iostat.cur, &tmp);
954 		u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
955 	}
956 }
957 
958 static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
959 {
960 	struct blkg_iostat_set *bis = &blkg->iostat;
961 	u64 rbytes, wbytes, rios, wios, dbytes, dios;
962 	const char *dname;
963 	unsigned seq;
964 	int i;
965 
966 	if (!blkg->online)
967 		return;
968 
969 	dname = blkg_dev_name(blkg);
970 	if (!dname)
971 		return;
972 
973 	seq_printf(s, "%s ", dname);
974 
975 	do {
976 		seq = u64_stats_fetch_begin(&bis->sync);
977 
978 		rbytes = bis->cur.bytes[BLKG_IOSTAT_READ];
979 		wbytes = bis->cur.bytes[BLKG_IOSTAT_WRITE];
980 		dbytes = bis->cur.bytes[BLKG_IOSTAT_DISCARD];
981 		rios = bis->cur.ios[BLKG_IOSTAT_READ];
982 		wios = bis->cur.ios[BLKG_IOSTAT_WRITE];
983 		dios = bis->cur.ios[BLKG_IOSTAT_DISCARD];
984 	} while (u64_stats_fetch_retry(&bis->sync, seq));
985 
986 	if (rbytes || wbytes || rios || wios) {
987 		seq_printf(s, "rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu",
988 			rbytes, wbytes, rios, wios,
989 			dbytes, dios);
990 	}
991 
992 	if (blkcg_debug_stats && atomic_read(&blkg->use_delay)) {
993 		seq_printf(s, " use_delay=%d delay_nsec=%llu",
994 			atomic_read(&blkg->use_delay),
995 			atomic64_read(&blkg->delay_nsec));
996 	}
997 
998 	for (i = 0; i < BLKCG_MAX_POLS; i++) {
999 		struct blkcg_policy *pol = blkcg_policy[i];
1000 
1001 		if (!blkg->pd[i] || !pol->pd_stat_fn)
1002 			continue;
1003 
1004 		pol->pd_stat_fn(blkg->pd[i], s);
1005 	}
1006 
1007 	seq_puts(s, "\n");
1008 }
1009 
1010 static int blkcg_print_stat(struct seq_file *sf, void *v)
1011 {
1012 	struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
1013 	struct blkcg_gq *blkg;
1014 
1015 	if (!seq_css(sf)->parent)
1016 		blkcg_fill_root_iostats();
1017 	else
1018 		cgroup_rstat_flush(blkcg->css.cgroup);
1019 
1020 	rcu_read_lock();
1021 	hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
1022 		spin_lock_irq(&blkg->q->queue_lock);
1023 		blkcg_print_one_stat(blkg, sf);
1024 		spin_unlock_irq(&blkg->q->queue_lock);
1025 	}
1026 	rcu_read_unlock();
1027 	return 0;
1028 }
1029 
1030 static struct cftype blkcg_files[] = {
1031 	{
1032 		.name = "stat",
1033 		.seq_show = blkcg_print_stat,
1034 	},
1035 	{ }	/* terminate */
1036 };
1037 
1038 static struct cftype blkcg_legacy_files[] = {
1039 	{
1040 		.name = "reset_stats",
1041 		.write_u64 = blkcg_reset_stats,
1042 	},
1043 	{ }	/* terminate */
1044 };
1045 
1046 #ifdef CONFIG_CGROUP_WRITEBACK
1047 struct list_head *blkcg_get_cgwb_list(struct cgroup_subsys_state *css)
1048 {
1049 	return &css_to_blkcg(css)->cgwb_list;
1050 }
1051 #endif
1052 
1053 /*
1054  * blkcg destruction is a three-stage process.
1055  *
1056  * 1. Destruction starts.  The blkcg_css_offline() callback is invoked
1057  *    which offlines writeback.  Here we tie the next stage of blkg destruction
1058  *    to the completion of writeback associated with the blkcg.  This lets us
1059  *    avoid punting potentially large amounts of outstanding writeback to root
1060  *    while maintaining any ongoing policies.  The next stage is triggered when
1061  *    the nr_cgwbs count goes to zero.
1062  *
1063  * 2. When the nr_cgwbs count goes to zero, blkcg_destroy_blkgs() is called
1064  *    and handles the destruction of blkgs.  Here the css reference held by
1065  *    the blkg is put back eventually allowing blkcg_css_free() to be called.
1066  *    This work may occur in cgwb_release_workfn() on the cgwb_release
1067  *    workqueue.  Any submitted ios that fail to get the blkg ref will be
1068  *    punted to the root_blkg.
1069  *
1070  * 3. Once the blkcg ref count goes to zero, blkcg_css_free() is called.
1071  *    This finally frees the blkcg.
1072  */
1073 
1074 /**
1075  * blkcg_destroy_blkgs - responsible for shooting down blkgs
1076  * @blkcg: blkcg of interest
1077  *
1078  * blkgs should be removed while holding both q and blkcg locks.  As blkcg lock
1079  * is nested inside q lock, this function performs reverse double lock dancing.
1080  * Destroying the blkgs releases the reference held on the blkcg's css allowing
1081  * blkcg_css_free to eventually be called.
1082  *
1083  * This is the blkcg counterpart of ioc_release_fn().
1084  */
1085 static void blkcg_destroy_blkgs(struct blkcg *blkcg)
1086 {
1087 	might_sleep();
1088 
1089 	spin_lock_irq(&blkcg->lock);
1090 
1091 	while (!hlist_empty(&blkcg->blkg_list)) {
1092 		struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
1093 						struct blkcg_gq, blkcg_node);
1094 		struct request_queue *q = blkg->q;
1095 
1096 		if (need_resched() || !spin_trylock(&q->queue_lock)) {
1097 			/*
1098 			 * Given that the system can accumulate a huge number
1099 			 * of blkgs in pathological cases, check to see if we
1100 			 * need to rescheduling to avoid softlockup.
1101 			 */
1102 			spin_unlock_irq(&blkcg->lock);
1103 			cond_resched();
1104 			spin_lock_irq(&blkcg->lock);
1105 			continue;
1106 		}
1107 
1108 		blkg_destroy(blkg);
1109 		spin_unlock(&q->queue_lock);
1110 	}
1111 
1112 	spin_unlock_irq(&blkcg->lock);
1113 }
1114 
1115 /**
1116  * blkcg_pin_online - pin online state
1117  * @blkcg_css: blkcg of interest
1118  *
1119  * While pinned, a blkcg is kept online.  This is primarily used to
1120  * impedance-match blkg and cgwb lifetimes so that blkg doesn't go offline
1121  * while an associated cgwb is still active.
1122  */
1123 void blkcg_pin_online(struct cgroup_subsys_state *blkcg_css)
1124 {
1125 	refcount_inc(&css_to_blkcg(blkcg_css)->online_pin);
1126 }
1127 
1128 /**
1129  * blkcg_unpin_online - unpin online state
1130  * @blkcg_css: blkcg of interest
1131  *
1132  * This is primarily used to impedance-match blkg and cgwb lifetimes so
1133  * that blkg doesn't go offline while an associated cgwb is still active.
1134  * When this count goes to zero, all active cgwbs have finished so the
1135  * blkcg can continue destruction by calling blkcg_destroy_blkgs().
1136  */
1137 void blkcg_unpin_online(struct cgroup_subsys_state *blkcg_css)
1138 {
1139 	struct blkcg *blkcg = css_to_blkcg(blkcg_css);
1140 
1141 	do {
1142 		if (!refcount_dec_and_test(&blkcg->online_pin))
1143 			break;
1144 		blkcg_destroy_blkgs(blkcg);
1145 		blkcg = blkcg_parent(blkcg);
1146 	} while (blkcg);
1147 }
1148 
1149 /**
1150  * blkcg_css_offline - cgroup css_offline callback
1151  * @css: css of interest
1152  *
1153  * This function is called when @css is about to go away.  Here the cgwbs are
1154  * offlined first and only once writeback associated with the blkcg has
1155  * finished do we start step 2 (see above).
1156  */
1157 static void blkcg_css_offline(struct cgroup_subsys_state *css)
1158 {
1159 	/* this prevents anyone from attaching or migrating to this blkcg */
1160 	wb_blkcg_offline(css);
1161 
1162 	/* put the base online pin allowing step 2 to be triggered */
1163 	blkcg_unpin_online(css);
1164 }
1165 
1166 static void blkcg_css_free(struct cgroup_subsys_state *css)
1167 {
1168 	struct blkcg *blkcg = css_to_blkcg(css);
1169 	int i;
1170 
1171 	mutex_lock(&blkcg_pol_mutex);
1172 
1173 	list_del(&blkcg->all_blkcgs_node);
1174 
1175 	for (i = 0; i < BLKCG_MAX_POLS; i++)
1176 		if (blkcg->cpd[i])
1177 			blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
1178 
1179 	mutex_unlock(&blkcg_pol_mutex);
1180 
1181 	free_percpu(blkcg->lhead);
1182 	kfree(blkcg);
1183 }
1184 
1185 static struct cgroup_subsys_state *
1186 blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
1187 {
1188 	struct blkcg *blkcg;
1189 	int i;
1190 
1191 	mutex_lock(&blkcg_pol_mutex);
1192 
1193 	if (!parent_css) {
1194 		blkcg = &blkcg_root;
1195 	} else {
1196 		blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
1197 		if (!blkcg)
1198 			goto unlock;
1199 	}
1200 
1201 	if (init_blkcg_llists(blkcg))
1202 		goto free_blkcg;
1203 
1204 	for (i = 0; i < BLKCG_MAX_POLS ; i++) {
1205 		struct blkcg_policy *pol = blkcg_policy[i];
1206 		struct blkcg_policy_data *cpd;
1207 
1208 		/*
1209 		 * If the policy hasn't been attached yet, wait for it
1210 		 * to be attached before doing anything else. Otherwise,
1211 		 * check if the policy requires any specific per-cgroup
1212 		 * data: if it does, allocate and initialize it.
1213 		 */
1214 		if (!pol || !pol->cpd_alloc_fn)
1215 			continue;
1216 
1217 		cpd = pol->cpd_alloc_fn(GFP_KERNEL);
1218 		if (!cpd)
1219 			goto free_pd_blkcg;
1220 
1221 		blkcg->cpd[i] = cpd;
1222 		cpd->blkcg = blkcg;
1223 		cpd->plid = i;
1224 		if (pol->cpd_init_fn)
1225 			pol->cpd_init_fn(cpd);
1226 	}
1227 
1228 	spin_lock_init(&blkcg->lock);
1229 	refcount_set(&blkcg->online_pin, 1);
1230 	INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT | __GFP_NOWARN);
1231 	INIT_HLIST_HEAD(&blkcg->blkg_list);
1232 #ifdef CONFIG_CGROUP_WRITEBACK
1233 	INIT_LIST_HEAD(&blkcg->cgwb_list);
1234 #endif
1235 	list_add_tail(&blkcg->all_blkcgs_node, &all_blkcgs);
1236 
1237 	mutex_unlock(&blkcg_pol_mutex);
1238 	return &blkcg->css;
1239 
1240 free_pd_blkcg:
1241 	for (i--; i >= 0; i--)
1242 		if (blkcg->cpd[i])
1243 			blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
1244 	free_percpu(blkcg->lhead);
1245 free_blkcg:
1246 	if (blkcg != &blkcg_root)
1247 		kfree(blkcg);
1248 unlock:
1249 	mutex_unlock(&blkcg_pol_mutex);
1250 	return ERR_PTR(-ENOMEM);
1251 }
1252 
1253 static int blkcg_css_online(struct cgroup_subsys_state *css)
1254 {
1255 	struct blkcg *parent = blkcg_parent(css_to_blkcg(css));
1256 
1257 	/*
1258 	 * blkcg_pin_online() is used to delay blkcg offline so that blkgs
1259 	 * don't go offline while cgwbs are still active on them.  Pin the
1260 	 * parent so that offline always happens towards the root.
1261 	 */
1262 	if (parent)
1263 		blkcg_pin_online(&parent->css);
1264 	return 0;
1265 }
1266 
1267 int blkcg_init_disk(struct gendisk *disk)
1268 {
1269 	struct request_queue *q = disk->queue;
1270 	struct blkcg_gq *new_blkg, *blkg;
1271 	bool preloaded;
1272 	int ret;
1273 
1274 	INIT_LIST_HEAD(&q->blkg_list);
1275 
1276 	new_blkg = blkg_alloc(&blkcg_root, disk, GFP_KERNEL);
1277 	if (!new_blkg)
1278 		return -ENOMEM;
1279 
1280 	preloaded = !radix_tree_preload(GFP_KERNEL);
1281 
1282 	/* Make sure the root blkg exists. */
1283 	/* spin_lock_irq can serve as RCU read-side critical section. */
1284 	spin_lock_irq(&q->queue_lock);
1285 	blkg = blkg_create(&blkcg_root, disk, new_blkg);
1286 	if (IS_ERR(blkg))
1287 		goto err_unlock;
1288 	q->root_blkg = blkg;
1289 	spin_unlock_irq(&q->queue_lock);
1290 
1291 	if (preloaded)
1292 		radix_tree_preload_end();
1293 
1294 	ret = blk_ioprio_init(disk);
1295 	if (ret)
1296 		goto err_destroy_all;
1297 
1298 	ret = blk_throtl_init(disk);
1299 	if (ret)
1300 		goto err_ioprio_exit;
1301 
1302 	ret = blk_iolatency_init(disk);
1303 	if (ret)
1304 		goto err_throtl_exit;
1305 
1306 	return 0;
1307 
1308 err_throtl_exit:
1309 	blk_throtl_exit(disk);
1310 err_ioprio_exit:
1311 	blk_ioprio_exit(disk);
1312 err_destroy_all:
1313 	blkg_destroy_all(disk);
1314 	return ret;
1315 err_unlock:
1316 	spin_unlock_irq(&q->queue_lock);
1317 	if (preloaded)
1318 		radix_tree_preload_end();
1319 	return PTR_ERR(blkg);
1320 }
1321 
1322 void blkcg_exit_disk(struct gendisk *disk)
1323 {
1324 	blkg_destroy_all(disk);
1325 	blk_throtl_exit(disk);
1326 }
1327 
1328 static void blkcg_bind(struct cgroup_subsys_state *root_css)
1329 {
1330 	int i;
1331 
1332 	mutex_lock(&blkcg_pol_mutex);
1333 
1334 	for (i = 0; i < BLKCG_MAX_POLS; i++) {
1335 		struct blkcg_policy *pol = blkcg_policy[i];
1336 		struct blkcg *blkcg;
1337 
1338 		if (!pol || !pol->cpd_bind_fn)
1339 			continue;
1340 
1341 		list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node)
1342 			if (blkcg->cpd[pol->plid])
1343 				pol->cpd_bind_fn(blkcg->cpd[pol->plid]);
1344 	}
1345 	mutex_unlock(&blkcg_pol_mutex);
1346 }
1347 
1348 static void blkcg_exit(struct task_struct *tsk)
1349 {
1350 	if (tsk->throttle_queue)
1351 		blk_put_queue(tsk->throttle_queue);
1352 	tsk->throttle_queue = NULL;
1353 }
1354 
1355 struct cgroup_subsys io_cgrp_subsys = {
1356 	.css_alloc = blkcg_css_alloc,
1357 	.css_online = blkcg_css_online,
1358 	.css_offline = blkcg_css_offline,
1359 	.css_free = blkcg_css_free,
1360 	.css_rstat_flush = blkcg_rstat_flush,
1361 	.bind = blkcg_bind,
1362 	.dfl_cftypes = blkcg_files,
1363 	.legacy_cftypes = blkcg_legacy_files,
1364 	.legacy_name = "blkio",
1365 	.exit = blkcg_exit,
1366 #ifdef CONFIG_MEMCG
1367 	/*
1368 	 * This ensures that, if available, memcg is automatically enabled
1369 	 * together on the default hierarchy so that the owner cgroup can
1370 	 * be retrieved from writeback pages.
1371 	 */
1372 	.depends_on = 1 << memory_cgrp_id,
1373 #endif
1374 };
1375 EXPORT_SYMBOL_GPL(io_cgrp_subsys);
1376 
1377 /**
1378  * blkcg_activate_policy - activate a blkcg policy on a request_queue
1379  * @q: request_queue of interest
1380  * @pol: blkcg policy to activate
1381  *
1382  * Activate @pol on @q.  Requires %GFP_KERNEL context.  @q goes through
1383  * bypass mode to populate its blkgs with policy_data for @pol.
1384  *
1385  * Activation happens with @q bypassed, so nobody would be accessing blkgs
1386  * from IO path.  Update of each blkg is protected by both queue and blkcg
1387  * locks so that holding either lock and testing blkcg_policy_enabled() is
1388  * always enough for dereferencing policy data.
1389  *
1390  * The caller is responsible for synchronizing [de]activations and policy
1391  * [un]registerations.  Returns 0 on success, -errno on failure.
1392  */
1393 int blkcg_activate_policy(struct request_queue *q,
1394 			  const struct blkcg_policy *pol)
1395 {
1396 	struct blkg_policy_data *pd_prealloc = NULL;
1397 	struct blkcg_gq *blkg, *pinned_blkg = NULL;
1398 	int ret;
1399 
1400 	if (blkcg_policy_enabled(q, pol))
1401 		return 0;
1402 
1403 	if (queue_is_mq(q))
1404 		blk_mq_freeze_queue(q);
1405 retry:
1406 	spin_lock_irq(&q->queue_lock);
1407 
1408 	/* blkg_list is pushed at the head, reverse walk to allocate parents first */
1409 	list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
1410 		struct blkg_policy_data *pd;
1411 
1412 		if (blkg->pd[pol->plid])
1413 			continue;
1414 
1415 		/* If prealloc matches, use it; otherwise try GFP_NOWAIT */
1416 		if (blkg == pinned_blkg) {
1417 			pd = pd_prealloc;
1418 			pd_prealloc = NULL;
1419 		} else {
1420 			pd = pol->pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN, q,
1421 					      blkg->blkcg);
1422 		}
1423 
1424 		if (!pd) {
1425 			/*
1426 			 * GFP_NOWAIT failed.  Free the existing one and
1427 			 * prealloc for @blkg w/ GFP_KERNEL.
1428 			 */
1429 			if (pinned_blkg)
1430 				blkg_put(pinned_blkg);
1431 			blkg_get(blkg);
1432 			pinned_blkg = blkg;
1433 
1434 			spin_unlock_irq(&q->queue_lock);
1435 
1436 			if (pd_prealloc)
1437 				pol->pd_free_fn(pd_prealloc);
1438 			pd_prealloc = pol->pd_alloc_fn(GFP_KERNEL, q,
1439 						       blkg->blkcg);
1440 			if (pd_prealloc)
1441 				goto retry;
1442 			else
1443 				goto enomem;
1444 		}
1445 
1446 		blkg->pd[pol->plid] = pd;
1447 		pd->blkg = blkg;
1448 		pd->plid = pol->plid;
1449 	}
1450 
1451 	/* all allocated, init in the same order */
1452 	if (pol->pd_init_fn)
1453 		list_for_each_entry_reverse(blkg, &q->blkg_list, q_node)
1454 			pol->pd_init_fn(blkg->pd[pol->plid]);
1455 
1456 	__set_bit(pol->plid, q->blkcg_pols);
1457 	ret = 0;
1458 
1459 	spin_unlock_irq(&q->queue_lock);
1460 out:
1461 	if (queue_is_mq(q))
1462 		blk_mq_unfreeze_queue(q);
1463 	if (pinned_blkg)
1464 		blkg_put(pinned_blkg);
1465 	if (pd_prealloc)
1466 		pol->pd_free_fn(pd_prealloc);
1467 	return ret;
1468 
1469 enomem:
1470 	/* alloc failed, nothing's initialized yet, free everything */
1471 	spin_lock_irq(&q->queue_lock);
1472 	list_for_each_entry(blkg, &q->blkg_list, q_node) {
1473 		struct blkcg *blkcg = blkg->blkcg;
1474 
1475 		spin_lock(&blkcg->lock);
1476 		if (blkg->pd[pol->plid]) {
1477 			pol->pd_free_fn(blkg->pd[pol->plid]);
1478 			blkg->pd[pol->plid] = NULL;
1479 		}
1480 		spin_unlock(&blkcg->lock);
1481 	}
1482 	spin_unlock_irq(&q->queue_lock);
1483 	ret = -ENOMEM;
1484 	goto out;
1485 }
1486 EXPORT_SYMBOL_GPL(blkcg_activate_policy);
1487 
1488 /**
1489  * blkcg_deactivate_policy - deactivate a blkcg policy on a request_queue
1490  * @q: request_queue of interest
1491  * @pol: blkcg policy to deactivate
1492  *
1493  * Deactivate @pol on @q.  Follows the same synchronization rules as
1494  * blkcg_activate_policy().
1495  */
1496 void blkcg_deactivate_policy(struct request_queue *q,
1497 			     const struct blkcg_policy *pol)
1498 {
1499 	struct blkcg_gq *blkg;
1500 
1501 	if (!blkcg_policy_enabled(q, pol))
1502 		return;
1503 
1504 	if (queue_is_mq(q))
1505 		blk_mq_freeze_queue(q);
1506 
1507 	spin_lock_irq(&q->queue_lock);
1508 
1509 	__clear_bit(pol->plid, q->blkcg_pols);
1510 
1511 	list_for_each_entry(blkg, &q->blkg_list, q_node) {
1512 		struct blkcg *blkcg = blkg->blkcg;
1513 
1514 		spin_lock(&blkcg->lock);
1515 		if (blkg->pd[pol->plid]) {
1516 			if (pol->pd_offline_fn)
1517 				pol->pd_offline_fn(blkg->pd[pol->plid]);
1518 			pol->pd_free_fn(blkg->pd[pol->plid]);
1519 			blkg->pd[pol->plid] = NULL;
1520 		}
1521 		spin_unlock(&blkcg->lock);
1522 	}
1523 
1524 	spin_unlock_irq(&q->queue_lock);
1525 
1526 	if (queue_is_mq(q))
1527 		blk_mq_unfreeze_queue(q);
1528 }
1529 EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
1530 
1531 static void blkcg_free_all_cpd(struct blkcg_policy *pol)
1532 {
1533 	struct blkcg *blkcg;
1534 
1535 	list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1536 		if (blkcg->cpd[pol->plid]) {
1537 			pol->cpd_free_fn(blkcg->cpd[pol->plid]);
1538 			blkcg->cpd[pol->plid] = NULL;
1539 		}
1540 	}
1541 }
1542 
1543 /**
1544  * blkcg_policy_register - register a blkcg policy
1545  * @pol: blkcg policy to register
1546  *
1547  * Register @pol with blkcg core.  Might sleep and @pol may be modified on
1548  * successful registration.  Returns 0 on success and -errno on failure.
1549  */
1550 int blkcg_policy_register(struct blkcg_policy *pol)
1551 {
1552 	struct blkcg *blkcg;
1553 	int i, ret;
1554 
1555 	mutex_lock(&blkcg_pol_register_mutex);
1556 	mutex_lock(&blkcg_pol_mutex);
1557 
1558 	/* find an empty slot */
1559 	ret = -ENOSPC;
1560 	for (i = 0; i < BLKCG_MAX_POLS; i++)
1561 		if (!blkcg_policy[i])
1562 			break;
1563 	if (i >= BLKCG_MAX_POLS) {
1564 		pr_warn("blkcg_policy_register: BLKCG_MAX_POLS too small\n");
1565 		goto err_unlock;
1566 	}
1567 
1568 	/* Make sure cpd/pd_alloc_fn and cpd/pd_free_fn in pairs */
1569 	if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
1570 		(!pol->pd_alloc_fn ^ !pol->pd_free_fn))
1571 		goto err_unlock;
1572 
1573 	/* register @pol */
1574 	pol->plid = i;
1575 	blkcg_policy[pol->plid] = pol;
1576 
1577 	/* allocate and install cpd's */
1578 	if (pol->cpd_alloc_fn) {
1579 		list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1580 			struct blkcg_policy_data *cpd;
1581 
1582 			cpd = pol->cpd_alloc_fn(GFP_KERNEL);
1583 			if (!cpd)
1584 				goto err_free_cpds;
1585 
1586 			blkcg->cpd[pol->plid] = cpd;
1587 			cpd->blkcg = blkcg;
1588 			cpd->plid = pol->plid;
1589 			if (pol->cpd_init_fn)
1590 				pol->cpd_init_fn(cpd);
1591 		}
1592 	}
1593 
1594 	mutex_unlock(&blkcg_pol_mutex);
1595 
1596 	/* everything is in place, add intf files for the new policy */
1597 	if (pol->dfl_cftypes)
1598 		WARN_ON(cgroup_add_dfl_cftypes(&io_cgrp_subsys,
1599 					       pol->dfl_cftypes));
1600 	if (pol->legacy_cftypes)
1601 		WARN_ON(cgroup_add_legacy_cftypes(&io_cgrp_subsys,
1602 						  pol->legacy_cftypes));
1603 	mutex_unlock(&blkcg_pol_register_mutex);
1604 	return 0;
1605 
1606 err_free_cpds:
1607 	if (pol->cpd_free_fn)
1608 		blkcg_free_all_cpd(pol);
1609 
1610 	blkcg_policy[pol->plid] = NULL;
1611 err_unlock:
1612 	mutex_unlock(&blkcg_pol_mutex);
1613 	mutex_unlock(&blkcg_pol_register_mutex);
1614 	return ret;
1615 }
1616 EXPORT_SYMBOL_GPL(blkcg_policy_register);
1617 
1618 /**
1619  * blkcg_policy_unregister - unregister a blkcg policy
1620  * @pol: blkcg policy to unregister
1621  *
1622  * Undo blkcg_policy_register(@pol).  Might sleep.
1623  */
1624 void blkcg_policy_unregister(struct blkcg_policy *pol)
1625 {
1626 	mutex_lock(&blkcg_pol_register_mutex);
1627 
1628 	if (WARN_ON(blkcg_policy[pol->plid] != pol))
1629 		goto out_unlock;
1630 
1631 	/* kill the intf files first */
1632 	if (pol->dfl_cftypes)
1633 		cgroup_rm_cftypes(pol->dfl_cftypes);
1634 	if (pol->legacy_cftypes)
1635 		cgroup_rm_cftypes(pol->legacy_cftypes);
1636 
1637 	/* remove cpds and unregister */
1638 	mutex_lock(&blkcg_pol_mutex);
1639 
1640 	if (pol->cpd_free_fn)
1641 		blkcg_free_all_cpd(pol);
1642 
1643 	blkcg_policy[pol->plid] = NULL;
1644 
1645 	mutex_unlock(&blkcg_pol_mutex);
1646 out_unlock:
1647 	mutex_unlock(&blkcg_pol_register_mutex);
1648 }
1649 EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
1650 
1651 bool __blkcg_punt_bio_submit(struct bio *bio)
1652 {
1653 	struct blkcg_gq *blkg = bio->bi_blkg;
1654 
1655 	/* consume the flag first */
1656 	bio->bi_opf &= ~REQ_CGROUP_PUNT;
1657 
1658 	/* never bounce for the root cgroup */
1659 	if (!blkg->parent)
1660 		return false;
1661 
1662 	spin_lock_bh(&blkg->async_bio_lock);
1663 	bio_list_add(&blkg->async_bios, bio);
1664 	spin_unlock_bh(&blkg->async_bio_lock);
1665 
1666 	queue_work(blkcg_punt_bio_wq, &blkg->async_bio_work);
1667 	return true;
1668 }
1669 
1670 /*
1671  * Scale the accumulated delay based on how long it has been since we updated
1672  * the delay.  We only call this when we are adding delay, in case it's been a
1673  * while since we added delay, and when we are checking to see if we need to
1674  * delay a task, to account for any delays that may have occurred.
1675  */
1676 static void blkcg_scale_delay(struct blkcg_gq *blkg, u64 now)
1677 {
1678 	u64 old = atomic64_read(&blkg->delay_start);
1679 
1680 	/* negative use_delay means no scaling, see blkcg_set_delay() */
1681 	if (atomic_read(&blkg->use_delay) < 0)
1682 		return;
1683 
1684 	/*
1685 	 * We only want to scale down every second.  The idea here is that we
1686 	 * want to delay people for min(delay_nsec, NSEC_PER_SEC) in a certain
1687 	 * time window.  We only want to throttle tasks for recent delay that
1688 	 * has occurred, in 1 second time windows since that's the maximum
1689 	 * things can be throttled.  We save the current delay window in
1690 	 * blkg->last_delay so we know what amount is still left to be charged
1691 	 * to the blkg from this point onward.  blkg->last_use keeps track of
1692 	 * the use_delay counter.  The idea is if we're unthrottling the blkg we
1693 	 * are ok with whatever is happening now, and we can take away more of
1694 	 * the accumulated delay as we've already throttled enough that
1695 	 * everybody is happy with their IO latencies.
1696 	 */
1697 	if (time_before64(old + NSEC_PER_SEC, now) &&
1698 	    atomic64_try_cmpxchg(&blkg->delay_start, &old, now)) {
1699 		u64 cur = atomic64_read(&blkg->delay_nsec);
1700 		u64 sub = min_t(u64, blkg->last_delay, now - old);
1701 		int cur_use = atomic_read(&blkg->use_delay);
1702 
1703 		/*
1704 		 * We've been unthrottled, subtract a larger chunk of our
1705 		 * accumulated delay.
1706 		 */
1707 		if (cur_use < blkg->last_use)
1708 			sub = max_t(u64, sub, blkg->last_delay >> 1);
1709 
1710 		/*
1711 		 * This shouldn't happen, but handle it anyway.  Our delay_nsec
1712 		 * should only ever be growing except here where we subtract out
1713 		 * min(last_delay, 1 second), but lord knows bugs happen and I'd
1714 		 * rather not end up with negative numbers.
1715 		 */
1716 		if (unlikely(cur < sub)) {
1717 			atomic64_set(&blkg->delay_nsec, 0);
1718 			blkg->last_delay = 0;
1719 		} else {
1720 			atomic64_sub(sub, &blkg->delay_nsec);
1721 			blkg->last_delay = cur - sub;
1722 		}
1723 		blkg->last_use = cur_use;
1724 	}
1725 }
1726 
1727 /*
1728  * This is called when we want to actually walk up the hierarchy and check to
1729  * see if we need to throttle, and then actually throttle if there is some
1730  * accumulated delay.  This should only be called upon return to user space so
1731  * we're not holding some lock that would induce a priority inversion.
1732  */
1733 static void blkcg_maybe_throttle_blkg(struct blkcg_gq *blkg, bool use_memdelay)
1734 {
1735 	unsigned long pflags;
1736 	bool clamp;
1737 	u64 now = ktime_to_ns(ktime_get());
1738 	u64 exp;
1739 	u64 delay_nsec = 0;
1740 	int tok;
1741 
1742 	while (blkg->parent) {
1743 		int use_delay = atomic_read(&blkg->use_delay);
1744 
1745 		if (use_delay) {
1746 			u64 this_delay;
1747 
1748 			blkcg_scale_delay(blkg, now);
1749 			this_delay = atomic64_read(&blkg->delay_nsec);
1750 			if (this_delay > delay_nsec) {
1751 				delay_nsec = this_delay;
1752 				clamp = use_delay > 0;
1753 			}
1754 		}
1755 		blkg = blkg->parent;
1756 	}
1757 
1758 	if (!delay_nsec)
1759 		return;
1760 
1761 	/*
1762 	 * Let's not sleep for all eternity if we've amassed a huge delay.
1763 	 * Swapping or metadata IO can accumulate 10's of seconds worth of
1764 	 * delay, and we want userspace to be able to do _something_ so cap the
1765 	 * delays at 0.25s. If there's 10's of seconds worth of delay then the
1766 	 * tasks will be delayed for 0.25 second for every syscall. If
1767 	 * blkcg_set_delay() was used as indicated by negative use_delay, the
1768 	 * caller is responsible for regulating the range.
1769 	 */
1770 	if (clamp)
1771 		delay_nsec = min_t(u64, delay_nsec, 250 * NSEC_PER_MSEC);
1772 
1773 	if (use_memdelay)
1774 		psi_memstall_enter(&pflags);
1775 
1776 	exp = ktime_add_ns(now, delay_nsec);
1777 	tok = io_schedule_prepare();
1778 	do {
1779 		__set_current_state(TASK_KILLABLE);
1780 		if (!schedule_hrtimeout(&exp, HRTIMER_MODE_ABS))
1781 			break;
1782 	} while (!fatal_signal_pending(current));
1783 	io_schedule_finish(tok);
1784 
1785 	if (use_memdelay)
1786 		psi_memstall_leave(&pflags);
1787 }
1788 
1789 /**
1790  * blkcg_maybe_throttle_current - throttle the current task if it has been marked
1791  *
1792  * This is only called if we've been marked with set_notify_resume().  Obviously
1793  * we can be set_notify_resume() for reasons other than blkcg throttling, so we
1794  * check to see if current->throttle_queue is set and if not this doesn't do
1795  * anything.  This should only ever be called by the resume code, it's not meant
1796  * to be called by people willy-nilly as it will actually do the work to
1797  * throttle the task if it is setup for throttling.
1798  */
1799 void blkcg_maybe_throttle_current(void)
1800 {
1801 	struct request_queue *q = current->throttle_queue;
1802 	struct blkcg *blkcg;
1803 	struct blkcg_gq *blkg;
1804 	bool use_memdelay = current->use_memdelay;
1805 
1806 	if (!q)
1807 		return;
1808 
1809 	current->throttle_queue = NULL;
1810 	current->use_memdelay = false;
1811 
1812 	rcu_read_lock();
1813 	blkcg = css_to_blkcg(blkcg_css());
1814 	if (!blkcg)
1815 		goto out;
1816 	blkg = blkg_lookup(blkcg, q);
1817 	if (!blkg)
1818 		goto out;
1819 	if (!blkg_tryget(blkg))
1820 		goto out;
1821 	rcu_read_unlock();
1822 
1823 	blkcg_maybe_throttle_blkg(blkg, use_memdelay);
1824 	blkg_put(blkg);
1825 	blk_put_queue(q);
1826 	return;
1827 out:
1828 	rcu_read_unlock();
1829 	blk_put_queue(q);
1830 }
1831 
1832 /**
1833  * blkcg_schedule_throttle - this task needs to check for throttling
1834  * @disk: disk to throttle
1835  * @use_memdelay: do we charge this to memory delay for PSI
1836  *
1837  * This is called by the IO controller when we know there's delay accumulated
1838  * for the blkg for this task.  We do not pass the blkg because there are places
1839  * we call this that may not have that information, the swapping code for
1840  * instance will only have a block_device at that point.  This set's the
1841  * notify_resume for the task to check and see if it requires throttling before
1842  * returning to user space.
1843  *
1844  * We will only schedule once per syscall.  You can call this over and over
1845  * again and it will only do the check once upon return to user space, and only
1846  * throttle once.  If the task needs to be throttled again it'll need to be
1847  * re-set at the next time we see the task.
1848  */
1849 void blkcg_schedule_throttle(struct gendisk *disk, bool use_memdelay)
1850 {
1851 	struct request_queue *q = disk->queue;
1852 
1853 	if (unlikely(current->flags & PF_KTHREAD))
1854 		return;
1855 
1856 	if (current->throttle_queue != q) {
1857 		if (!blk_get_queue(q))
1858 			return;
1859 
1860 		if (current->throttle_queue)
1861 			blk_put_queue(current->throttle_queue);
1862 		current->throttle_queue = q;
1863 	}
1864 
1865 	if (use_memdelay)
1866 		current->use_memdelay = use_memdelay;
1867 	set_notify_resume(current);
1868 }
1869 
1870 /**
1871  * blkcg_add_delay - add delay to this blkg
1872  * @blkg: blkg of interest
1873  * @now: the current time in nanoseconds
1874  * @delta: how many nanoseconds of delay to add
1875  *
1876  * Charge @delta to the blkg's current delay accumulation.  This is used to
1877  * throttle tasks if an IO controller thinks we need more throttling.
1878  */
1879 void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta)
1880 {
1881 	if (WARN_ON_ONCE(atomic_read(&blkg->use_delay) < 0))
1882 		return;
1883 	blkcg_scale_delay(blkg, now);
1884 	atomic64_add(delta, &blkg->delay_nsec);
1885 }
1886 
1887 /**
1888  * blkg_tryget_closest - try and get a blkg ref on the closet blkg
1889  * @bio: target bio
1890  * @css: target css
1891  *
1892  * As the failure mode here is to walk up the blkg tree, this ensure that the
1893  * blkg->parent pointers are always valid.  This returns the blkg that it ended
1894  * up taking a reference on or %NULL if no reference was taken.
1895  */
1896 static inline struct blkcg_gq *blkg_tryget_closest(struct bio *bio,
1897 		struct cgroup_subsys_state *css)
1898 {
1899 	struct blkcg_gq *blkg, *ret_blkg = NULL;
1900 
1901 	rcu_read_lock();
1902 	blkg = blkg_lookup_create(css_to_blkcg(css), bio->bi_bdev->bd_disk);
1903 	while (blkg) {
1904 		if (blkg_tryget(blkg)) {
1905 			ret_blkg = blkg;
1906 			break;
1907 		}
1908 		blkg = blkg->parent;
1909 	}
1910 	rcu_read_unlock();
1911 
1912 	return ret_blkg;
1913 }
1914 
1915 /**
1916  * bio_associate_blkg_from_css - associate a bio with a specified css
1917  * @bio: target bio
1918  * @css: target css
1919  *
1920  * Associate @bio with the blkg found by combining the css's blkg and the
1921  * request_queue of the @bio.  An association failure is handled by walking up
1922  * the blkg tree.  Therefore, the blkg associated can be anything between @blkg
1923  * and q->root_blkg.  This situation only happens when a cgroup is dying and
1924  * then the remaining bios will spill to the closest alive blkg.
1925  *
1926  * A reference will be taken on the blkg and will be released when @bio is
1927  * freed.
1928  */
1929 void bio_associate_blkg_from_css(struct bio *bio,
1930 				 struct cgroup_subsys_state *css)
1931 {
1932 	if (bio->bi_blkg)
1933 		blkg_put(bio->bi_blkg);
1934 
1935 	if (css && css->parent) {
1936 		bio->bi_blkg = blkg_tryget_closest(bio, css);
1937 	} else {
1938 		blkg_get(bdev_get_queue(bio->bi_bdev)->root_blkg);
1939 		bio->bi_blkg = bdev_get_queue(bio->bi_bdev)->root_blkg;
1940 	}
1941 }
1942 EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
1943 
1944 /**
1945  * bio_associate_blkg - associate a bio with a blkg
1946  * @bio: target bio
1947  *
1948  * Associate @bio with the blkg found from the bio's css and request_queue.
1949  * If one is not found, bio_lookup_blkg() creates the blkg.  If a blkg is
1950  * already associated, the css is reused and association redone as the
1951  * request_queue may have changed.
1952  */
1953 void bio_associate_blkg(struct bio *bio)
1954 {
1955 	struct cgroup_subsys_state *css;
1956 
1957 	rcu_read_lock();
1958 
1959 	if (bio->bi_blkg)
1960 		css = bio_blkcg_css(bio);
1961 	else
1962 		css = blkcg_css();
1963 
1964 	bio_associate_blkg_from_css(bio, css);
1965 
1966 	rcu_read_unlock();
1967 }
1968 EXPORT_SYMBOL_GPL(bio_associate_blkg);
1969 
1970 /**
1971  * bio_clone_blkg_association - clone blkg association from src to dst bio
1972  * @dst: destination bio
1973  * @src: source bio
1974  */
1975 void bio_clone_blkg_association(struct bio *dst, struct bio *src)
1976 {
1977 	if (src->bi_blkg)
1978 		bio_associate_blkg_from_css(dst, bio_blkcg_css(src));
1979 }
1980 EXPORT_SYMBOL_GPL(bio_clone_blkg_association);
1981 
1982 static int blk_cgroup_io_type(struct bio *bio)
1983 {
1984 	if (op_is_discard(bio->bi_opf))
1985 		return BLKG_IOSTAT_DISCARD;
1986 	if (op_is_write(bio->bi_opf))
1987 		return BLKG_IOSTAT_WRITE;
1988 	return BLKG_IOSTAT_READ;
1989 }
1990 
1991 void blk_cgroup_bio_start(struct bio *bio)
1992 {
1993 	struct blkcg *blkcg = bio->bi_blkg->blkcg;
1994 	int rwd = blk_cgroup_io_type(bio), cpu;
1995 	struct blkg_iostat_set *bis;
1996 	unsigned long flags;
1997 
1998 	cpu = get_cpu();
1999 	bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
2000 	flags = u64_stats_update_begin_irqsave(&bis->sync);
2001 
2002 	/*
2003 	 * If the bio is flagged with BIO_CGROUP_ACCT it means this is a split
2004 	 * bio and we would have already accounted for the size of the bio.
2005 	 */
2006 	if (!bio_flagged(bio, BIO_CGROUP_ACCT)) {
2007 		bio_set_flag(bio, BIO_CGROUP_ACCT);
2008 		bis->cur.bytes[rwd] += bio->bi_iter.bi_size;
2009 	}
2010 	bis->cur.ios[rwd]++;
2011 
2012 	/*
2013 	 * If the iostat_cpu isn't in a lockless list, put it into the
2014 	 * list to indicate that a stat update is pending.
2015 	 */
2016 	if (!READ_ONCE(bis->lqueued)) {
2017 		struct llist_head *lhead = this_cpu_ptr(blkcg->lhead);
2018 
2019 		llist_add(&bis->lnode, lhead);
2020 		WRITE_ONCE(bis->lqueued, true);
2021 		percpu_ref_get(&bis->blkg->refcnt);
2022 	}
2023 
2024 	u64_stats_update_end_irqrestore(&bis->sync, flags);
2025 	if (cgroup_subsys_on_dfl(io_cgrp_subsys))
2026 		cgroup_rstat_updated(blkcg->css.cgroup, cpu);
2027 	put_cpu();
2028 }
2029 
2030 bool blk_cgroup_congested(void)
2031 {
2032 	struct cgroup_subsys_state *css;
2033 	bool ret = false;
2034 
2035 	rcu_read_lock();
2036 	for (css = blkcg_css(); css; css = css->parent) {
2037 		if (atomic_read(&css->cgroup->congestion_count)) {
2038 			ret = true;
2039 			break;
2040 		}
2041 	}
2042 	rcu_read_unlock();
2043 	return ret;
2044 }
2045 
2046 static int __init blkcg_init(void)
2047 {
2048 	blkcg_punt_bio_wq = alloc_workqueue("blkcg_punt_bio",
2049 					    WQ_MEM_RECLAIM | WQ_FREEZABLE |
2050 					    WQ_UNBOUND | WQ_SYSFS, 0);
2051 	if (!blkcg_punt_bio_wq)
2052 		return -ENOMEM;
2053 	return 0;
2054 }
2055 subsys_initcall(blkcg_init);
2056 
2057 module_param(blkcg_debug_stats, bool, 0644);
2058 MODULE_PARM_DESC(blkcg_debug_stats, "True if you want debug stats, false if not");
2059