xref: /openbmc/linux/fs/super.c (revision 3c881e05c814c970e4f9577446a9d3461d134607)
1  // SPDX-License-Identifier: GPL-2.0
2  /*
3   *  linux/fs/super.c
4   *
5   *  Copyright (C) 1991, 1992  Linus Torvalds
6   *
7   *  super.c contains code to handle: - mount structures
8   *                                   - super-block tables
9   *                                   - filesystem drivers list
10   *                                   - mount system call
11   *                                   - umount system call
12   *                                   - ustat system call
13   *
14   * GK 2/5/95  -  Changed to support mounting the root fs via NFS
15   *
16   *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
17   *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
18   *  Added options to /proc/mounts:
19   *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
20   *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
21   *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
22   */
23  
24  #include <linux/export.h>
25  #include <linux/slab.h>
26  #include <linux/blkdev.h>
27  #include <linux/mount.h>
28  #include <linux/security.h>
29  #include <linux/writeback.h>		/* for the emergency remount stuff */
30  #include <linux/idr.h>
31  #include <linux/mutex.h>
32  #include <linux/backing-dev.h>
33  #include <linux/rculist_bl.h>
34  #include <linux/cleancache.h>
35  #include <linux/fscrypt.h>
36  #include <linux/fsnotify.h>
37  #include <linux/lockdep.h>
38  #include <linux/user_namespace.h>
39  #include <linux/fs_context.h>
40  #include <uapi/linux/mount.h>
41  #include "internal.h"
42  
43  static int thaw_super_locked(struct super_block *sb);
44  
45  static LIST_HEAD(super_blocks);
46  static DEFINE_SPINLOCK(sb_lock);
47  
48  static char *sb_writers_name[SB_FREEZE_LEVELS] = {
49  	"sb_writers",
50  	"sb_pagefaults",
51  	"sb_internal",
52  };
53  
54  /*
55   * One thing we have to be careful of with a per-sb shrinker is that we don't
56   * drop the last active reference to the superblock from within the shrinker.
57   * If that happens we could trigger unregistering the shrinker from within the
58   * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
59   * take a passive reference to the superblock to avoid this from occurring.
60   */
61  static unsigned long super_cache_scan(struct shrinker *shrink,
62  				      struct shrink_control *sc)
63  {
64  	struct super_block *sb;
65  	long	fs_objects = 0;
66  	long	total_objects;
67  	long	freed = 0;
68  	long	dentries;
69  	long	inodes;
70  
71  	sb = container_of(shrink, struct super_block, s_shrink);
72  
73  	/*
74  	 * Deadlock avoidance.  We may hold various FS locks, and we don't want
75  	 * to recurse into the FS that called us in clear_inode() and friends..
76  	 */
77  	if (!(sc->gfp_mask & __GFP_FS))
78  		return SHRINK_STOP;
79  
80  	if (!trylock_super(sb))
81  		return SHRINK_STOP;
82  
83  	if (sb->s_op->nr_cached_objects)
84  		fs_objects = sb->s_op->nr_cached_objects(sb, sc);
85  
86  	inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
87  	dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc);
88  	total_objects = dentries + inodes + fs_objects + 1;
89  	if (!total_objects)
90  		total_objects = 1;
91  
92  	/* proportion the scan between the caches */
93  	dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);
94  	inodes = mult_frac(sc->nr_to_scan, inodes, total_objects);
95  	fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
96  
97  	/*
98  	 * prune the dcache first as the icache is pinned by it, then
99  	 * prune the icache, followed by the filesystem specific caches
100  	 *
101  	 * Ensure that we always scan at least one object - memcg kmem
102  	 * accounting uses this to fully empty the caches.
103  	 */
104  	sc->nr_to_scan = dentries + 1;
105  	freed = prune_dcache_sb(sb, sc);
106  	sc->nr_to_scan = inodes + 1;
107  	freed += prune_icache_sb(sb, sc);
108  
109  	if (fs_objects) {
110  		sc->nr_to_scan = fs_objects + 1;
111  		freed += sb->s_op->free_cached_objects(sb, sc);
112  	}
113  
114  	up_read(&sb->s_umount);
115  	return freed;
116  }
117  
118  static unsigned long super_cache_count(struct shrinker *shrink,
119  				       struct shrink_control *sc)
120  {
121  	struct super_block *sb;
122  	long	total_objects = 0;
123  
124  	sb = container_of(shrink, struct super_block, s_shrink);
125  
126  	/*
127  	 * We don't call trylock_super() here as it is a scalability bottleneck,
128  	 * so we're exposed to partial setup state. The shrinker rwsem does not
129  	 * protect filesystem operations backing list_lru_shrink_count() or
130  	 * s_op->nr_cached_objects(). Counts can change between
131  	 * super_cache_count and super_cache_scan, so we really don't need locks
132  	 * here.
133  	 *
134  	 * However, if we are currently mounting the superblock, the underlying
135  	 * filesystem might be in a state of partial construction and hence it
136  	 * is dangerous to access it.  trylock_super() uses a SB_BORN check to
137  	 * avoid this situation, so do the same here. The memory barrier is
138  	 * matched with the one in mount_fs() as we don't hold locks here.
139  	 */
140  	if (!(sb->s_flags & SB_BORN))
141  		return 0;
142  	smp_rmb();
143  
144  	if (sb->s_op && sb->s_op->nr_cached_objects)
145  		total_objects = sb->s_op->nr_cached_objects(sb, sc);
146  
147  	total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
148  	total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
149  
150  	if (!total_objects)
151  		return SHRINK_EMPTY;
152  
153  	total_objects = vfs_pressure_ratio(total_objects);
154  	return total_objects;
155  }
156  
157  static void destroy_super_work(struct work_struct *work)
158  {
159  	struct super_block *s = container_of(work, struct super_block,
160  							destroy_work);
161  	int i;
162  
163  	for (i = 0; i < SB_FREEZE_LEVELS; i++)
164  		percpu_free_rwsem(&s->s_writers.rw_sem[i]);
165  	kfree(s);
166  }
167  
168  static void destroy_super_rcu(struct rcu_head *head)
169  {
170  	struct super_block *s = container_of(head, struct super_block, rcu);
171  	INIT_WORK(&s->destroy_work, destroy_super_work);
172  	schedule_work(&s->destroy_work);
173  }
174  
175  /* Free a superblock that has never been seen by anyone */
176  static void destroy_unused_super(struct super_block *s)
177  {
178  	if (!s)
179  		return;
180  	up_write(&s->s_umount);
181  	list_lru_destroy(&s->s_dentry_lru);
182  	list_lru_destroy(&s->s_inode_lru);
183  	security_sb_free(s);
184  	put_user_ns(s->s_user_ns);
185  	kfree(s->s_subtype);
186  	free_prealloced_shrinker(&s->s_shrink);
187  	/* no delays needed */
188  	destroy_super_work(&s->destroy_work);
189  }
190  
191  /**
192   *	alloc_super	-	create new superblock
193   *	@type:	filesystem type superblock should belong to
194   *	@flags: the mount flags
195   *	@user_ns: User namespace for the super_block
196   *
197   *	Allocates and initializes a new &struct super_block.  alloc_super()
198   *	returns a pointer new superblock or %NULL if allocation had failed.
199   */
200  static struct super_block *alloc_super(struct file_system_type *type, int flags,
201  				       struct user_namespace *user_ns)
202  {
203  	struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
204  	static const struct super_operations default_op;
205  	int i;
206  
207  	if (!s)
208  		return NULL;
209  
210  	INIT_LIST_HEAD(&s->s_mounts);
211  	s->s_user_ns = get_user_ns(user_ns);
212  	init_rwsem(&s->s_umount);
213  	lockdep_set_class(&s->s_umount, &type->s_umount_key);
214  	/*
215  	 * sget() can have s_umount recursion.
216  	 *
217  	 * When it cannot find a suitable sb, it allocates a new
218  	 * one (this one), and tries again to find a suitable old
219  	 * one.
220  	 *
221  	 * In case that succeeds, it will acquire the s_umount
222  	 * lock of the old one. Since these are clearly distrinct
223  	 * locks, and this object isn't exposed yet, there's no
224  	 * risk of deadlocks.
225  	 *
226  	 * Annotate this by putting this lock in a different
227  	 * subclass.
228  	 */
229  	down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
230  
231  	if (security_sb_alloc(s))
232  		goto fail;
233  
234  	for (i = 0; i < SB_FREEZE_LEVELS; i++) {
235  		if (__percpu_init_rwsem(&s->s_writers.rw_sem[i],
236  					sb_writers_name[i],
237  					&type->s_writers_key[i]))
238  			goto fail;
239  	}
240  	init_waitqueue_head(&s->s_writers.wait_unfrozen);
241  	s->s_bdi = &noop_backing_dev_info;
242  	s->s_flags = flags;
243  	if (s->s_user_ns != &init_user_ns)
244  		s->s_iflags |= SB_I_NODEV;
245  	INIT_HLIST_NODE(&s->s_instances);
246  	INIT_HLIST_BL_HEAD(&s->s_roots);
247  	mutex_init(&s->s_sync_lock);
248  	INIT_LIST_HEAD(&s->s_inodes);
249  	spin_lock_init(&s->s_inode_list_lock);
250  	INIT_LIST_HEAD(&s->s_inodes_wb);
251  	spin_lock_init(&s->s_inode_wblist_lock);
252  
253  	s->s_count = 1;
254  	atomic_set(&s->s_active, 1);
255  	mutex_init(&s->s_vfs_rename_mutex);
256  	lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
257  	init_rwsem(&s->s_dquot.dqio_sem);
258  	s->s_maxbytes = MAX_NON_LFS;
259  	s->s_op = &default_op;
260  	s->s_time_gran = 1000000000;
261  	s->s_time_min = TIME64_MIN;
262  	s->s_time_max = TIME64_MAX;
263  	s->cleancache_poolid = CLEANCACHE_NO_POOL;
264  
265  	s->s_shrink.seeks = DEFAULT_SEEKS;
266  	s->s_shrink.scan_objects = super_cache_scan;
267  	s->s_shrink.count_objects = super_cache_count;
268  	s->s_shrink.batch = 1024;
269  	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
270  	if (prealloc_shrinker(&s->s_shrink))
271  		goto fail;
272  	if (list_lru_init_memcg(&s->s_dentry_lru, &s->s_shrink))
273  		goto fail;
274  	if (list_lru_init_memcg(&s->s_inode_lru, &s->s_shrink))
275  		goto fail;
276  	return s;
277  
278  fail:
279  	destroy_unused_super(s);
280  	return NULL;
281  }
282  
283  /* Superblock refcounting  */
284  
285  /*
286   * Drop a superblock's refcount.  The caller must hold sb_lock.
287   */
288  static void __put_super(struct super_block *s)
289  {
290  	if (!--s->s_count) {
291  		list_del_init(&s->s_list);
292  		WARN_ON(s->s_dentry_lru.node);
293  		WARN_ON(s->s_inode_lru.node);
294  		WARN_ON(!list_empty(&s->s_mounts));
295  		security_sb_free(s);
296  		fscrypt_sb_free(s);
297  		put_user_ns(s->s_user_ns);
298  		kfree(s->s_subtype);
299  		call_rcu(&s->rcu, destroy_super_rcu);
300  	}
301  }
302  
303  /**
304   *	put_super	-	drop a temporary reference to superblock
305   *	@sb: superblock in question
306   *
307   *	Drops a temporary reference, frees superblock if there's no
308   *	references left.
309   */
310  void put_super(struct super_block *sb)
311  {
312  	spin_lock(&sb_lock);
313  	__put_super(sb);
314  	spin_unlock(&sb_lock);
315  }
316  
317  
318  /**
319   *	deactivate_locked_super	-	drop an active reference to superblock
320   *	@s: superblock to deactivate
321   *
322   *	Drops an active reference to superblock, converting it into a temporary
323   *	one if there is no other active references left.  In that case we
324   *	tell fs driver to shut it down and drop the temporary reference we
325   *	had just acquired.
326   *
327   *	Caller holds exclusive lock on superblock; that lock is released.
328   */
329  void deactivate_locked_super(struct super_block *s)
330  {
331  	struct file_system_type *fs = s->s_type;
332  	if (atomic_dec_and_test(&s->s_active)) {
333  		cleancache_invalidate_fs(s);
334  		unregister_shrinker(&s->s_shrink);
335  		fs->kill_sb(s);
336  
337  		/*
338  		 * Since list_lru_destroy() may sleep, we cannot call it from
339  		 * put_super(), where we hold the sb_lock. Therefore we destroy
340  		 * the lru lists right now.
341  		 */
342  		list_lru_destroy(&s->s_dentry_lru);
343  		list_lru_destroy(&s->s_inode_lru);
344  
345  		put_filesystem(fs);
346  		put_super(s);
347  	} else {
348  		up_write(&s->s_umount);
349  	}
350  }
351  
352  EXPORT_SYMBOL(deactivate_locked_super);
353  
354  /**
355   *	deactivate_super	-	drop an active reference to superblock
356   *	@s: superblock to deactivate
357   *
358   *	Variant of deactivate_locked_super(), except that superblock is *not*
359   *	locked by caller.  If we are going to drop the final active reference,
360   *	lock will be acquired prior to that.
361   */
362  void deactivate_super(struct super_block *s)
363  {
364  	if (!atomic_add_unless(&s->s_active, -1, 1)) {
365  		down_write(&s->s_umount);
366  		deactivate_locked_super(s);
367  	}
368  }
369  
370  EXPORT_SYMBOL(deactivate_super);
371  
372  /**
373   *	grab_super - acquire an active reference
374   *	@s: reference we are trying to make active
375   *
376   *	Tries to acquire an active reference.  grab_super() is used when we
377   * 	had just found a superblock in super_blocks or fs_type->fs_supers
378   *	and want to turn it into a full-blown active reference.  grab_super()
379   *	is called with sb_lock held and drops it.  Returns 1 in case of
380   *	success, 0 if we had failed (superblock contents was already dead or
381   *	dying when grab_super() had been called).  Note that this is only
382   *	called for superblocks not in rundown mode (== ones still on ->fs_supers
383   *	of their type), so increment of ->s_count is OK here.
384   */
385  static int grab_super(struct super_block *s) __releases(sb_lock)
386  {
387  	s->s_count++;
388  	spin_unlock(&sb_lock);
389  	down_write(&s->s_umount);
390  	if ((s->s_flags & SB_BORN) && atomic_inc_not_zero(&s->s_active)) {
391  		put_super(s);
392  		return 1;
393  	}
394  	up_write(&s->s_umount);
395  	put_super(s);
396  	return 0;
397  }
398  
399  /*
400   *	trylock_super - try to grab ->s_umount shared
401   *	@sb: reference we are trying to grab
402   *
403   *	Try to prevent fs shutdown.  This is used in places where we
404   *	cannot take an active reference but we need to ensure that the
405   *	filesystem is not shut down while we are working on it. It returns
406   *	false if we cannot acquire s_umount or if we lose the race and
407   *	filesystem already got into shutdown, and returns true with the s_umount
408   *	lock held in read mode in case of success. On successful return,
409   *	the caller must drop the s_umount lock when done.
410   *
411   *	Note that unlike get_super() et.al. this one does *not* bump ->s_count.
412   *	The reason why it's safe is that we are OK with doing trylock instead
413   *	of down_read().  There's a couple of places that are OK with that, but
414   *	it's very much not a general-purpose interface.
415   */
416  bool trylock_super(struct super_block *sb)
417  {
418  	if (down_read_trylock(&sb->s_umount)) {
419  		if (!hlist_unhashed(&sb->s_instances) &&
420  		    sb->s_root && (sb->s_flags & SB_BORN))
421  			return true;
422  		up_read(&sb->s_umount);
423  	}
424  
425  	return false;
426  }
427  
428  /**
429   *	generic_shutdown_super	-	common helper for ->kill_sb()
430   *	@sb: superblock to kill
431   *
432   *	generic_shutdown_super() does all fs-independent work on superblock
433   *	shutdown.  Typical ->kill_sb() should pick all fs-specific objects
434   *	that need destruction out of superblock, call generic_shutdown_super()
435   *	and release aforementioned objects.  Note: dentries and inodes _are_
436   *	taken care of and do not need specific handling.
437   *
438   *	Upon calling this function, the filesystem may no longer alter or
439   *	rearrange the set of dentries belonging to this super_block, nor may it
440   *	change the attachments of dentries to inodes.
441   */
442  void generic_shutdown_super(struct super_block *sb)
443  {
444  	const struct super_operations *sop = sb->s_op;
445  
446  	if (sb->s_root) {
447  		shrink_dcache_for_umount(sb);
448  		sync_filesystem(sb);
449  		sb->s_flags &= ~SB_ACTIVE;
450  
451  		cgroup_writeback_umount();
452  
453  		/* evict all inodes with zero refcount */
454  		evict_inodes(sb);
455  		/* only nonzero refcount inodes can have marks */
456  		fsnotify_sb_delete(sb);
457  		security_sb_delete(sb);
458  
459  		if (sb->s_dio_done_wq) {
460  			destroy_workqueue(sb->s_dio_done_wq);
461  			sb->s_dio_done_wq = NULL;
462  		}
463  
464  		if (sop->put_super)
465  			sop->put_super(sb);
466  
467  		if (!list_empty(&sb->s_inodes)) {
468  			printk("VFS: Busy inodes after unmount of %s. "
469  			   "Self-destruct in 5 seconds.  Have a nice day...\n",
470  			   sb->s_id);
471  		}
472  	}
473  	spin_lock(&sb_lock);
474  	/* should be initialized for __put_super_and_need_restart() */
475  	hlist_del_init(&sb->s_instances);
476  	spin_unlock(&sb_lock);
477  	up_write(&sb->s_umount);
478  	if (sb->s_bdi != &noop_backing_dev_info) {
479  		bdi_put(sb->s_bdi);
480  		sb->s_bdi = &noop_backing_dev_info;
481  	}
482  }
483  
484  EXPORT_SYMBOL(generic_shutdown_super);
485  
486  bool mount_capable(struct fs_context *fc)
487  {
488  	if (!(fc->fs_type->fs_flags & FS_USERNS_MOUNT))
489  		return capable(CAP_SYS_ADMIN);
490  	else
491  		return ns_capable(fc->user_ns, CAP_SYS_ADMIN);
492  }
493  
494  /**
495   * sget_fc - Find or create a superblock
496   * @fc:	Filesystem context.
497   * @test: Comparison callback
498   * @set: Setup callback
499   *
500   * Find or create a superblock using the parameters stored in the filesystem
501   * context and the two callback functions.
502   *
503   * If an extant superblock is matched, then that will be returned with an
504   * elevated reference count that the caller must transfer or discard.
505   *
506   * If no match is made, a new superblock will be allocated and basic
507   * initialisation will be performed (s_type, s_fs_info and s_id will be set and
508   * the set() callback will be invoked), the superblock will be published and it
509   * will be returned in a partially constructed state with SB_BORN and SB_ACTIVE
510   * as yet unset.
511   */
512  struct super_block *sget_fc(struct fs_context *fc,
513  			    int (*test)(struct super_block *, struct fs_context *),
514  			    int (*set)(struct super_block *, struct fs_context *))
515  {
516  	struct super_block *s = NULL;
517  	struct super_block *old;
518  	struct user_namespace *user_ns = fc->global ? &init_user_ns : fc->user_ns;
519  	int err;
520  
521  retry:
522  	spin_lock(&sb_lock);
523  	if (test) {
524  		hlist_for_each_entry(old, &fc->fs_type->fs_supers, s_instances) {
525  			if (test(old, fc))
526  				goto share_extant_sb;
527  		}
528  	}
529  	if (!s) {
530  		spin_unlock(&sb_lock);
531  		s = alloc_super(fc->fs_type, fc->sb_flags, user_ns);
532  		if (!s)
533  			return ERR_PTR(-ENOMEM);
534  		goto retry;
535  	}
536  
537  	s->s_fs_info = fc->s_fs_info;
538  	err = set(s, fc);
539  	if (err) {
540  		s->s_fs_info = NULL;
541  		spin_unlock(&sb_lock);
542  		destroy_unused_super(s);
543  		return ERR_PTR(err);
544  	}
545  	fc->s_fs_info = NULL;
546  	s->s_type = fc->fs_type;
547  	s->s_iflags |= fc->s_iflags;
548  	strlcpy(s->s_id, s->s_type->name, sizeof(s->s_id));
549  	list_add_tail(&s->s_list, &super_blocks);
550  	hlist_add_head(&s->s_instances, &s->s_type->fs_supers);
551  	spin_unlock(&sb_lock);
552  	get_filesystem(s->s_type);
553  	register_shrinker_prepared(&s->s_shrink);
554  	return s;
555  
556  share_extant_sb:
557  	if (user_ns != old->s_user_ns) {
558  		spin_unlock(&sb_lock);
559  		destroy_unused_super(s);
560  		return ERR_PTR(-EBUSY);
561  	}
562  	if (!grab_super(old))
563  		goto retry;
564  	destroy_unused_super(s);
565  	return old;
566  }
567  EXPORT_SYMBOL(sget_fc);
568  
569  /**
570   *	sget	-	find or create a superblock
571   *	@type:	  filesystem type superblock should belong to
572   *	@test:	  comparison callback
573   *	@set:	  setup callback
574   *	@flags:	  mount flags
575   *	@data:	  argument to each of them
576   */
577  struct super_block *sget(struct file_system_type *type,
578  			int (*test)(struct super_block *,void *),
579  			int (*set)(struct super_block *,void *),
580  			int flags,
581  			void *data)
582  {
583  	struct user_namespace *user_ns = current_user_ns();
584  	struct super_block *s = NULL;
585  	struct super_block *old;
586  	int err;
587  
588  	/* We don't yet pass the user namespace of the parent
589  	 * mount through to here so always use &init_user_ns
590  	 * until that changes.
591  	 */
592  	if (flags & SB_SUBMOUNT)
593  		user_ns = &init_user_ns;
594  
595  retry:
596  	spin_lock(&sb_lock);
597  	if (test) {
598  		hlist_for_each_entry(old, &type->fs_supers, s_instances) {
599  			if (!test(old, data))
600  				continue;
601  			if (user_ns != old->s_user_ns) {
602  				spin_unlock(&sb_lock);
603  				destroy_unused_super(s);
604  				return ERR_PTR(-EBUSY);
605  			}
606  			if (!grab_super(old))
607  				goto retry;
608  			destroy_unused_super(s);
609  			return old;
610  		}
611  	}
612  	if (!s) {
613  		spin_unlock(&sb_lock);
614  		s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
615  		if (!s)
616  			return ERR_PTR(-ENOMEM);
617  		goto retry;
618  	}
619  
620  	err = set(s, data);
621  	if (err) {
622  		spin_unlock(&sb_lock);
623  		destroy_unused_super(s);
624  		return ERR_PTR(err);
625  	}
626  	s->s_type = type;
627  	strlcpy(s->s_id, type->name, sizeof(s->s_id));
628  	list_add_tail(&s->s_list, &super_blocks);
629  	hlist_add_head(&s->s_instances, &type->fs_supers);
630  	spin_unlock(&sb_lock);
631  	get_filesystem(type);
632  	register_shrinker_prepared(&s->s_shrink);
633  	return s;
634  }
635  EXPORT_SYMBOL(sget);
636  
637  void drop_super(struct super_block *sb)
638  {
639  	up_read(&sb->s_umount);
640  	put_super(sb);
641  }
642  
643  EXPORT_SYMBOL(drop_super);
644  
645  void drop_super_exclusive(struct super_block *sb)
646  {
647  	up_write(&sb->s_umount);
648  	put_super(sb);
649  }
650  EXPORT_SYMBOL(drop_super_exclusive);
651  
652  static void __iterate_supers(void (*f)(struct super_block *))
653  {
654  	struct super_block *sb, *p = NULL;
655  
656  	spin_lock(&sb_lock);
657  	list_for_each_entry(sb, &super_blocks, s_list) {
658  		if (hlist_unhashed(&sb->s_instances))
659  			continue;
660  		sb->s_count++;
661  		spin_unlock(&sb_lock);
662  
663  		f(sb);
664  
665  		spin_lock(&sb_lock);
666  		if (p)
667  			__put_super(p);
668  		p = sb;
669  	}
670  	if (p)
671  		__put_super(p);
672  	spin_unlock(&sb_lock);
673  }
674  /**
675   *	iterate_supers - call function for all active superblocks
676   *	@f: function to call
677   *	@arg: argument to pass to it
678   *
679   *	Scans the superblock list and calls given function, passing it
680   *	locked superblock and given argument.
681   */
682  void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
683  {
684  	struct super_block *sb, *p = NULL;
685  
686  	spin_lock(&sb_lock);
687  	list_for_each_entry(sb, &super_blocks, s_list) {
688  		if (hlist_unhashed(&sb->s_instances))
689  			continue;
690  		sb->s_count++;
691  		spin_unlock(&sb_lock);
692  
693  		down_read(&sb->s_umount);
694  		if (sb->s_root && (sb->s_flags & SB_BORN))
695  			f(sb, arg);
696  		up_read(&sb->s_umount);
697  
698  		spin_lock(&sb_lock);
699  		if (p)
700  			__put_super(p);
701  		p = sb;
702  	}
703  	if (p)
704  		__put_super(p);
705  	spin_unlock(&sb_lock);
706  }
707  
708  /**
709   *	iterate_supers_type - call function for superblocks of given type
710   *	@type: fs type
711   *	@f: function to call
712   *	@arg: argument to pass to it
713   *
714   *	Scans the superblock list and calls given function, passing it
715   *	locked superblock and given argument.
716   */
717  void iterate_supers_type(struct file_system_type *type,
718  	void (*f)(struct super_block *, void *), void *arg)
719  {
720  	struct super_block *sb, *p = NULL;
721  
722  	spin_lock(&sb_lock);
723  	hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
724  		sb->s_count++;
725  		spin_unlock(&sb_lock);
726  
727  		down_read(&sb->s_umount);
728  		if (sb->s_root && (sb->s_flags & SB_BORN))
729  			f(sb, arg);
730  		up_read(&sb->s_umount);
731  
732  		spin_lock(&sb_lock);
733  		if (p)
734  			__put_super(p);
735  		p = sb;
736  	}
737  	if (p)
738  		__put_super(p);
739  	spin_unlock(&sb_lock);
740  }
741  
742  EXPORT_SYMBOL(iterate_supers_type);
743  
744  /**
745   * get_super - get the superblock of a device
746   * @bdev: device to get the superblock for
747   *
748   * Scans the superblock list and finds the superblock of the file system
749   * mounted on the device given. %NULL is returned if no match is found.
750   */
751  struct super_block *get_super(struct block_device *bdev)
752  {
753  	struct super_block *sb;
754  
755  	if (!bdev)
756  		return NULL;
757  
758  	spin_lock(&sb_lock);
759  rescan:
760  	list_for_each_entry(sb, &super_blocks, s_list) {
761  		if (hlist_unhashed(&sb->s_instances))
762  			continue;
763  		if (sb->s_bdev == bdev) {
764  			sb->s_count++;
765  			spin_unlock(&sb_lock);
766  			down_read(&sb->s_umount);
767  			/* still alive? */
768  			if (sb->s_root && (sb->s_flags & SB_BORN))
769  				return sb;
770  			up_read(&sb->s_umount);
771  			/* nope, got unmounted */
772  			spin_lock(&sb_lock);
773  			__put_super(sb);
774  			goto rescan;
775  		}
776  	}
777  	spin_unlock(&sb_lock);
778  	return NULL;
779  }
780  
781  /**
782   * get_active_super - get an active reference to the superblock of a device
783   * @bdev: device to get the superblock for
784   *
785   * Scans the superblock list and finds the superblock of the file system
786   * mounted on the device given.  Returns the superblock with an active
787   * reference or %NULL if none was found.
788   */
789  struct super_block *get_active_super(struct block_device *bdev)
790  {
791  	struct super_block *sb;
792  
793  	if (!bdev)
794  		return NULL;
795  
796  restart:
797  	spin_lock(&sb_lock);
798  	list_for_each_entry(sb, &super_blocks, s_list) {
799  		if (hlist_unhashed(&sb->s_instances))
800  			continue;
801  		if (sb->s_bdev == bdev) {
802  			if (!grab_super(sb))
803  				goto restart;
804  			up_write(&sb->s_umount);
805  			return sb;
806  		}
807  	}
808  	spin_unlock(&sb_lock);
809  	return NULL;
810  }
811  
812  struct super_block *user_get_super(dev_t dev, bool excl)
813  {
814  	struct super_block *sb;
815  
816  	spin_lock(&sb_lock);
817  rescan:
818  	list_for_each_entry(sb, &super_blocks, s_list) {
819  		if (hlist_unhashed(&sb->s_instances))
820  			continue;
821  		if (sb->s_dev ==  dev) {
822  			sb->s_count++;
823  			spin_unlock(&sb_lock);
824  			if (excl)
825  				down_write(&sb->s_umount);
826  			else
827  				down_read(&sb->s_umount);
828  			/* still alive? */
829  			if (sb->s_root && (sb->s_flags & SB_BORN))
830  				return sb;
831  			if (excl)
832  				up_write(&sb->s_umount);
833  			else
834  				up_read(&sb->s_umount);
835  			/* nope, got unmounted */
836  			spin_lock(&sb_lock);
837  			__put_super(sb);
838  			goto rescan;
839  		}
840  	}
841  	spin_unlock(&sb_lock);
842  	return NULL;
843  }
844  
845  /**
846   * reconfigure_super - asks filesystem to change superblock parameters
847   * @fc: The superblock and configuration
848   *
849   * Alters the configuration parameters of a live superblock.
850   */
851  int reconfigure_super(struct fs_context *fc)
852  {
853  	struct super_block *sb = fc->root->d_sb;
854  	int retval;
855  	bool remount_ro = false;
856  	bool force = fc->sb_flags & SB_FORCE;
857  
858  	if (fc->sb_flags_mask & ~MS_RMT_MASK)
859  		return -EINVAL;
860  	if (sb->s_writers.frozen != SB_UNFROZEN)
861  		return -EBUSY;
862  
863  	retval = security_sb_remount(sb, fc->security);
864  	if (retval)
865  		return retval;
866  
867  	if (fc->sb_flags_mask & SB_RDONLY) {
868  #ifdef CONFIG_BLOCK
869  		if (!(fc->sb_flags & SB_RDONLY) && sb->s_bdev &&
870  		    bdev_read_only(sb->s_bdev))
871  			return -EACCES;
872  #endif
873  
874  		remount_ro = (fc->sb_flags & SB_RDONLY) && !sb_rdonly(sb);
875  	}
876  
877  	if (remount_ro) {
878  		if (!hlist_empty(&sb->s_pins)) {
879  			up_write(&sb->s_umount);
880  			group_pin_kill(&sb->s_pins);
881  			down_write(&sb->s_umount);
882  			if (!sb->s_root)
883  				return 0;
884  			if (sb->s_writers.frozen != SB_UNFROZEN)
885  				return -EBUSY;
886  			remount_ro = !sb_rdonly(sb);
887  		}
888  	}
889  	shrink_dcache_sb(sb);
890  
891  	/* If we are reconfiguring to RDONLY and current sb is read/write,
892  	 * make sure there are no files open for writing.
893  	 */
894  	if (remount_ro) {
895  		if (force) {
896  			sb->s_readonly_remount = 1;
897  			smp_wmb();
898  		} else {
899  			retval = sb_prepare_remount_readonly(sb);
900  			if (retval)
901  				return retval;
902  		}
903  	}
904  
905  	if (fc->ops->reconfigure) {
906  		retval = fc->ops->reconfigure(fc);
907  		if (retval) {
908  			if (!force)
909  				goto cancel_readonly;
910  			/* If forced remount, go ahead despite any errors */
911  			WARN(1, "forced remount of a %s fs returned %i\n",
912  			     sb->s_type->name, retval);
913  		}
914  	}
915  
916  	WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) |
917  				 (fc->sb_flags & fc->sb_flags_mask)));
918  	/* Needs to be ordered wrt mnt_is_readonly() */
919  	smp_wmb();
920  	sb->s_readonly_remount = 0;
921  
922  	/*
923  	 * Some filesystems modify their metadata via some other path than the
924  	 * bdev buffer cache (eg. use a private mapping, or directories in
925  	 * pagecache, etc). Also file data modifications go via their own
926  	 * mappings. So If we try to mount readonly then copy the filesystem
927  	 * from bdev, we could get stale data, so invalidate it to give a best
928  	 * effort at coherency.
929  	 */
930  	if (remount_ro && sb->s_bdev)
931  		invalidate_bdev(sb->s_bdev);
932  	return 0;
933  
934  cancel_readonly:
935  	sb->s_readonly_remount = 0;
936  	return retval;
937  }
938  
939  static void do_emergency_remount_callback(struct super_block *sb)
940  {
941  	down_write(&sb->s_umount);
942  	if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
943  	    !sb_rdonly(sb)) {
944  		struct fs_context *fc;
945  
946  		fc = fs_context_for_reconfigure(sb->s_root,
947  					SB_RDONLY | SB_FORCE, SB_RDONLY);
948  		if (!IS_ERR(fc)) {
949  			if (parse_monolithic_mount_data(fc, NULL) == 0)
950  				(void)reconfigure_super(fc);
951  			put_fs_context(fc);
952  		}
953  	}
954  	up_write(&sb->s_umount);
955  }
956  
957  static void do_emergency_remount(struct work_struct *work)
958  {
959  	__iterate_supers(do_emergency_remount_callback);
960  	kfree(work);
961  	printk("Emergency Remount complete\n");
962  }
963  
964  void emergency_remount(void)
965  {
966  	struct work_struct *work;
967  
968  	work = kmalloc(sizeof(*work), GFP_ATOMIC);
969  	if (work) {
970  		INIT_WORK(work, do_emergency_remount);
971  		schedule_work(work);
972  	}
973  }
974  
975  static void do_thaw_all_callback(struct super_block *sb)
976  {
977  	down_write(&sb->s_umount);
978  	if (sb->s_root && sb->s_flags & SB_BORN) {
979  		emergency_thaw_bdev(sb);
980  		thaw_super_locked(sb);
981  	} else {
982  		up_write(&sb->s_umount);
983  	}
984  }
985  
986  static void do_thaw_all(struct work_struct *work)
987  {
988  	__iterate_supers(do_thaw_all_callback);
989  	kfree(work);
990  	printk(KERN_WARNING "Emergency Thaw complete\n");
991  }
992  
993  /**
994   * emergency_thaw_all -- forcibly thaw every frozen filesystem
995   *
996   * Used for emergency unfreeze of all filesystems via SysRq
997   */
998  void emergency_thaw_all(void)
999  {
1000  	struct work_struct *work;
1001  
1002  	work = kmalloc(sizeof(*work), GFP_ATOMIC);
1003  	if (work) {
1004  		INIT_WORK(work, do_thaw_all);
1005  		schedule_work(work);
1006  	}
1007  }
1008  
1009  static DEFINE_IDA(unnamed_dev_ida);
1010  
1011  /**
1012   * get_anon_bdev - Allocate a block device for filesystems which don't have one.
1013   * @p: Pointer to a dev_t.
1014   *
1015   * Filesystems which don't use real block devices can call this function
1016   * to allocate a virtual block device.
1017   *
1018   * Context: Any context.  Frequently called while holding sb_lock.
1019   * Return: 0 on success, -EMFILE if there are no anonymous bdevs left
1020   * or -ENOMEM if memory allocation failed.
1021   */
1022  int get_anon_bdev(dev_t *p)
1023  {
1024  	int dev;
1025  
1026  	/*
1027  	 * Many userspace utilities consider an FSID of 0 invalid.
1028  	 * Always return at least 1 from get_anon_bdev.
1029  	 */
1030  	dev = ida_alloc_range(&unnamed_dev_ida, 1, (1 << MINORBITS) - 1,
1031  			GFP_ATOMIC);
1032  	if (dev == -ENOSPC)
1033  		dev = -EMFILE;
1034  	if (dev < 0)
1035  		return dev;
1036  
1037  	*p = MKDEV(0, dev);
1038  	return 0;
1039  }
1040  EXPORT_SYMBOL(get_anon_bdev);
1041  
1042  void free_anon_bdev(dev_t dev)
1043  {
1044  	ida_free(&unnamed_dev_ida, MINOR(dev));
1045  }
1046  EXPORT_SYMBOL(free_anon_bdev);
1047  
1048  int set_anon_super(struct super_block *s, void *data)
1049  {
1050  	return get_anon_bdev(&s->s_dev);
1051  }
1052  EXPORT_SYMBOL(set_anon_super);
1053  
1054  void kill_anon_super(struct super_block *sb)
1055  {
1056  	dev_t dev = sb->s_dev;
1057  	generic_shutdown_super(sb);
1058  	free_anon_bdev(dev);
1059  }
1060  EXPORT_SYMBOL(kill_anon_super);
1061  
1062  void kill_litter_super(struct super_block *sb)
1063  {
1064  	if (sb->s_root)
1065  		d_genocide(sb->s_root);
1066  	kill_anon_super(sb);
1067  }
1068  EXPORT_SYMBOL(kill_litter_super);
1069  
1070  int set_anon_super_fc(struct super_block *sb, struct fs_context *fc)
1071  {
1072  	return set_anon_super(sb, NULL);
1073  }
1074  EXPORT_SYMBOL(set_anon_super_fc);
1075  
1076  static int test_keyed_super(struct super_block *sb, struct fs_context *fc)
1077  {
1078  	return sb->s_fs_info == fc->s_fs_info;
1079  }
1080  
1081  static int test_single_super(struct super_block *s, struct fs_context *fc)
1082  {
1083  	return 1;
1084  }
1085  
1086  /**
1087   * vfs_get_super - Get a superblock with a search key set in s_fs_info.
1088   * @fc: The filesystem context holding the parameters
1089   * @keying: How to distinguish superblocks
1090   * @fill_super: Helper to initialise a new superblock
1091   *
1092   * Search for a superblock and create a new one if not found.  The search
1093   * criterion is controlled by @keying.  If the search fails, a new superblock
1094   * is created and @fill_super() is called to initialise it.
1095   *
1096   * @keying can take one of a number of values:
1097   *
1098   * (1) vfs_get_single_super - Only one superblock of this type may exist on the
1099   *     system.  This is typically used for special system filesystems.
1100   *
1101   * (2) vfs_get_keyed_super - Multiple superblocks may exist, but they must have
1102   *     distinct keys (where the key is in s_fs_info).  Searching for the same
1103   *     key again will turn up the superblock for that key.
1104   *
1105   * (3) vfs_get_independent_super - Multiple superblocks may exist and are
1106   *     unkeyed.  Each call will get a new superblock.
1107   *
1108   * A permissions check is made by sget_fc() unless we're getting a superblock
1109   * for a kernel-internal mount or a submount.
1110   */
1111  int vfs_get_super(struct fs_context *fc,
1112  		  enum vfs_get_super_keying keying,
1113  		  int (*fill_super)(struct super_block *sb,
1114  				    struct fs_context *fc))
1115  {
1116  	int (*test)(struct super_block *, struct fs_context *);
1117  	struct super_block *sb;
1118  	int err;
1119  
1120  	switch (keying) {
1121  	case vfs_get_single_super:
1122  	case vfs_get_single_reconf_super:
1123  		test = test_single_super;
1124  		break;
1125  	case vfs_get_keyed_super:
1126  		test = test_keyed_super;
1127  		break;
1128  	case vfs_get_independent_super:
1129  		test = NULL;
1130  		break;
1131  	default:
1132  		BUG();
1133  	}
1134  
1135  	sb = sget_fc(fc, test, set_anon_super_fc);
1136  	if (IS_ERR(sb))
1137  		return PTR_ERR(sb);
1138  
1139  	if (!sb->s_root) {
1140  		err = fill_super(sb, fc);
1141  		if (err)
1142  			goto error;
1143  
1144  		sb->s_flags |= SB_ACTIVE;
1145  		fc->root = dget(sb->s_root);
1146  	} else {
1147  		fc->root = dget(sb->s_root);
1148  		if (keying == vfs_get_single_reconf_super) {
1149  			err = reconfigure_super(fc);
1150  			if (err < 0) {
1151  				dput(fc->root);
1152  				fc->root = NULL;
1153  				goto error;
1154  			}
1155  		}
1156  	}
1157  
1158  	return 0;
1159  
1160  error:
1161  	deactivate_locked_super(sb);
1162  	return err;
1163  }
1164  EXPORT_SYMBOL(vfs_get_super);
1165  
1166  int get_tree_nodev(struct fs_context *fc,
1167  		  int (*fill_super)(struct super_block *sb,
1168  				    struct fs_context *fc))
1169  {
1170  	return vfs_get_super(fc, vfs_get_independent_super, fill_super);
1171  }
1172  EXPORT_SYMBOL(get_tree_nodev);
1173  
1174  int get_tree_single(struct fs_context *fc,
1175  		  int (*fill_super)(struct super_block *sb,
1176  				    struct fs_context *fc))
1177  {
1178  	return vfs_get_super(fc, vfs_get_single_super, fill_super);
1179  }
1180  EXPORT_SYMBOL(get_tree_single);
1181  
1182  int get_tree_single_reconf(struct fs_context *fc,
1183  		  int (*fill_super)(struct super_block *sb,
1184  				    struct fs_context *fc))
1185  {
1186  	return vfs_get_super(fc, vfs_get_single_reconf_super, fill_super);
1187  }
1188  EXPORT_SYMBOL(get_tree_single_reconf);
1189  
1190  int get_tree_keyed(struct fs_context *fc,
1191  		  int (*fill_super)(struct super_block *sb,
1192  				    struct fs_context *fc),
1193  		void *key)
1194  {
1195  	fc->s_fs_info = key;
1196  	return vfs_get_super(fc, vfs_get_keyed_super, fill_super);
1197  }
1198  EXPORT_SYMBOL(get_tree_keyed);
1199  
1200  #ifdef CONFIG_BLOCK
1201  
1202  static int set_bdev_super(struct super_block *s, void *data)
1203  {
1204  	s->s_bdev = data;
1205  	s->s_dev = s->s_bdev->bd_dev;
1206  	s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
1207  
1208  	if (blk_queue_stable_writes(s->s_bdev->bd_disk->queue))
1209  		s->s_iflags |= SB_I_STABLE_WRITES;
1210  	return 0;
1211  }
1212  
1213  static int set_bdev_super_fc(struct super_block *s, struct fs_context *fc)
1214  {
1215  	return set_bdev_super(s, fc->sget_key);
1216  }
1217  
1218  static int test_bdev_super_fc(struct super_block *s, struct fs_context *fc)
1219  {
1220  	return s->s_bdev == fc->sget_key;
1221  }
1222  
1223  /**
1224   * get_tree_bdev - Get a superblock based on a single block device
1225   * @fc: The filesystem context holding the parameters
1226   * @fill_super: Helper to initialise a new superblock
1227   */
1228  int get_tree_bdev(struct fs_context *fc,
1229  		int (*fill_super)(struct super_block *,
1230  				  struct fs_context *))
1231  {
1232  	struct block_device *bdev;
1233  	struct super_block *s;
1234  	fmode_t mode = FMODE_READ | FMODE_EXCL;
1235  	int error = 0;
1236  
1237  	if (!(fc->sb_flags & SB_RDONLY))
1238  		mode |= FMODE_WRITE;
1239  
1240  	if (!fc->source)
1241  		return invalf(fc, "No source specified");
1242  
1243  	bdev = blkdev_get_by_path(fc->source, mode, fc->fs_type);
1244  	if (IS_ERR(bdev)) {
1245  		errorf(fc, "%s: Can't open blockdev", fc->source);
1246  		return PTR_ERR(bdev);
1247  	}
1248  
1249  	/* Once the superblock is inserted into the list by sget_fc(), s_umount
1250  	 * will protect the lockfs code from trying to start a snapshot while
1251  	 * we are mounting
1252  	 */
1253  	mutex_lock(&bdev->bd_fsfreeze_mutex);
1254  	if (bdev->bd_fsfreeze_count > 0) {
1255  		mutex_unlock(&bdev->bd_fsfreeze_mutex);
1256  		warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
1257  		blkdev_put(bdev, mode);
1258  		return -EBUSY;
1259  	}
1260  
1261  	fc->sb_flags |= SB_NOSEC;
1262  	fc->sget_key = bdev;
1263  	s = sget_fc(fc, test_bdev_super_fc, set_bdev_super_fc);
1264  	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1265  	if (IS_ERR(s)) {
1266  		blkdev_put(bdev, mode);
1267  		return PTR_ERR(s);
1268  	}
1269  
1270  	if (s->s_root) {
1271  		/* Don't summarily change the RO/RW state. */
1272  		if ((fc->sb_flags ^ s->s_flags) & SB_RDONLY) {
1273  			warnf(fc, "%pg: Can't mount, would change RO state", bdev);
1274  			deactivate_locked_super(s);
1275  			blkdev_put(bdev, mode);
1276  			return -EBUSY;
1277  		}
1278  
1279  		/*
1280  		 * s_umount nests inside bd_mutex during
1281  		 * __invalidate_device().  blkdev_put() acquires
1282  		 * bd_mutex and can't be called under s_umount.  Drop
1283  		 * s_umount temporarily.  This is safe as we're
1284  		 * holding an active reference.
1285  		 */
1286  		up_write(&s->s_umount);
1287  		blkdev_put(bdev, mode);
1288  		down_write(&s->s_umount);
1289  	} else {
1290  		s->s_mode = mode;
1291  		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1292  		sb_set_blocksize(s, block_size(bdev));
1293  		error = fill_super(s, fc);
1294  		if (error) {
1295  			deactivate_locked_super(s);
1296  			return error;
1297  		}
1298  
1299  		s->s_flags |= SB_ACTIVE;
1300  		bdev->bd_super = s;
1301  	}
1302  
1303  	BUG_ON(fc->root);
1304  	fc->root = dget(s->s_root);
1305  	return 0;
1306  }
1307  EXPORT_SYMBOL(get_tree_bdev);
1308  
1309  static int test_bdev_super(struct super_block *s, void *data)
1310  {
1311  	return (void *)s->s_bdev == data;
1312  }
1313  
1314  struct dentry *mount_bdev(struct file_system_type *fs_type,
1315  	int flags, const char *dev_name, void *data,
1316  	int (*fill_super)(struct super_block *, void *, int))
1317  {
1318  	struct block_device *bdev;
1319  	struct super_block *s;
1320  	fmode_t mode = FMODE_READ | FMODE_EXCL;
1321  	int error = 0;
1322  
1323  	if (!(flags & SB_RDONLY))
1324  		mode |= FMODE_WRITE;
1325  
1326  	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
1327  	if (IS_ERR(bdev))
1328  		return ERR_CAST(bdev);
1329  
1330  	/*
1331  	 * once the super is inserted into the list by sget, s_umount
1332  	 * will protect the lockfs code from trying to start a snapshot
1333  	 * while we are mounting
1334  	 */
1335  	mutex_lock(&bdev->bd_fsfreeze_mutex);
1336  	if (bdev->bd_fsfreeze_count > 0) {
1337  		mutex_unlock(&bdev->bd_fsfreeze_mutex);
1338  		error = -EBUSY;
1339  		goto error_bdev;
1340  	}
1341  	s = sget(fs_type, test_bdev_super, set_bdev_super, flags | SB_NOSEC,
1342  		 bdev);
1343  	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1344  	if (IS_ERR(s))
1345  		goto error_s;
1346  
1347  	if (s->s_root) {
1348  		if ((flags ^ s->s_flags) & SB_RDONLY) {
1349  			deactivate_locked_super(s);
1350  			error = -EBUSY;
1351  			goto error_bdev;
1352  		}
1353  
1354  		/*
1355  		 * s_umount nests inside bd_mutex during
1356  		 * __invalidate_device().  blkdev_put() acquires
1357  		 * bd_mutex and can't be called under s_umount.  Drop
1358  		 * s_umount temporarily.  This is safe as we're
1359  		 * holding an active reference.
1360  		 */
1361  		up_write(&s->s_umount);
1362  		blkdev_put(bdev, mode);
1363  		down_write(&s->s_umount);
1364  	} else {
1365  		s->s_mode = mode;
1366  		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1367  		sb_set_blocksize(s, block_size(bdev));
1368  		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1369  		if (error) {
1370  			deactivate_locked_super(s);
1371  			goto error;
1372  		}
1373  
1374  		s->s_flags |= SB_ACTIVE;
1375  		bdev->bd_super = s;
1376  	}
1377  
1378  	return dget(s->s_root);
1379  
1380  error_s:
1381  	error = PTR_ERR(s);
1382  error_bdev:
1383  	blkdev_put(bdev, mode);
1384  error:
1385  	return ERR_PTR(error);
1386  }
1387  EXPORT_SYMBOL(mount_bdev);
1388  
1389  void kill_block_super(struct super_block *sb)
1390  {
1391  	struct block_device *bdev = sb->s_bdev;
1392  	fmode_t mode = sb->s_mode;
1393  
1394  	bdev->bd_super = NULL;
1395  	generic_shutdown_super(sb);
1396  	sync_blockdev(bdev);
1397  	WARN_ON_ONCE(!(mode & FMODE_EXCL));
1398  	blkdev_put(bdev, mode | FMODE_EXCL);
1399  }
1400  
1401  EXPORT_SYMBOL(kill_block_super);
1402  #endif
1403  
1404  struct dentry *mount_nodev(struct file_system_type *fs_type,
1405  	int flags, void *data,
1406  	int (*fill_super)(struct super_block *, void *, int))
1407  {
1408  	int error;
1409  	struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1410  
1411  	if (IS_ERR(s))
1412  		return ERR_CAST(s);
1413  
1414  	error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1415  	if (error) {
1416  		deactivate_locked_super(s);
1417  		return ERR_PTR(error);
1418  	}
1419  	s->s_flags |= SB_ACTIVE;
1420  	return dget(s->s_root);
1421  }
1422  EXPORT_SYMBOL(mount_nodev);
1423  
1424  static int reconfigure_single(struct super_block *s,
1425  			      int flags, void *data)
1426  {
1427  	struct fs_context *fc;
1428  	int ret;
1429  
1430  	/* The caller really need to be passing fc down into mount_single(),
1431  	 * then a chunk of this can be removed.  [Bollocks -- AV]
1432  	 * Better yet, reconfiguration shouldn't happen, but rather the second
1433  	 * mount should be rejected if the parameters are not compatible.
1434  	 */
1435  	fc = fs_context_for_reconfigure(s->s_root, flags, MS_RMT_MASK);
1436  	if (IS_ERR(fc))
1437  		return PTR_ERR(fc);
1438  
1439  	ret = parse_monolithic_mount_data(fc, data);
1440  	if (ret < 0)
1441  		goto out;
1442  
1443  	ret = reconfigure_super(fc);
1444  out:
1445  	put_fs_context(fc);
1446  	return ret;
1447  }
1448  
1449  static int compare_single(struct super_block *s, void *p)
1450  {
1451  	return 1;
1452  }
1453  
1454  struct dentry *mount_single(struct file_system_type *fs_type,
1455  	int flags, void *data,
1456  	int (*fill_super)(struct super_block *, void *, int))
1457  {
1458  	struct super_block *s;
1459  	int error;
1460  
1461  	s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1462  	if (IS_ERR(s))
1463  		return ERR_CAST(s);
1464  	if (!s->s_root) {
1465  		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1466  		if (!error)
1467  			s->s_flags |= SB_ACTIVE;
1468  	} else {
1469  		error = reconfigure_single(s, flags, data);
1470  	}
1471  	if (unlikely(error)) {
1472  		deactivate_locked_super(s);
1473  		return ERR_PTR(error);
1474  	}
1475  	return dget(s->s_root);
1476  }
1477  EXPORT_SYMBOL(mount_single);
1478  
1479  /**
1480   * vfs_get_tree - Get the mountable root
1481   * @fc: The superblock configuration context.
1482   *
1483   * The filesystem is invoked to get or create a superblock which can then later
1484   * be used for mounting.  The filesystem places a pointer to the root to be
1485   * used for mounting in @fc->root.
1486   */
1487  int vfs_get_tree(struct fs_context *fc)
1488  {
1489  	struct super_block *sb;
1490  	int error;
1491  
1492  	if (fc->root)
1493  		return -EBUSY;
1494  
1495  	/* Get the mountable root in fc->root, with a ref on the root and a ref
1496  	 * on the superblock.
1497  	 */
1498  	error = fc->ops->get_tree(fc);
1499  	if (error < 0)
1500  		return error;
1501  
1502  	if (!fc->root) {
1503  		pr_err("Filesystem %s get_tree() didn't set fc->root\n",
1504  		       fc->fs_type->name);
1505  		/* We don't know what the locking state of the superblock is -
1506  		 * if there is a superblock.
1507  		 */
1508  		BUG();
1509  	}
1510  
1511  	sb = fc->root->d_sb;
1512  	WARN_ON(!sb->s_bdi);
1513  
1514  	/*
1515  	 * Write barrier is for super_cache_count(). We place it before setting
1516  	 * SB_BORN as the data dependency between the two functions is the
1517  	 * superblock structure contents that we just set up, not the SB_BORN
1518  	 * flag.
1519  	 */
1520  	smp_wmb();
1521  	sb->s_flags |= SB_BORN;
1522  
1523  	error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
1524  	if (unlikely(error)) {
1525  		fc_drop_locked(fc);
1526  		return error;
1527  	}
1528  
1529  	/*
1530  	 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1531  	 * but s_maxbytes was an unsigned long long for many releases. Throw
1532  	 * this warning for a little while to try and catch filesystems that
1533  	 * violate this rule.
1534  	 */
1535  	WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1536  		"negative value (%lld)\n", fc->fs_type->name, sb->s_maxbytes);
1537  
1538  	return 0;
1539  }
1540  EXPORT_SYMBOL(vfs_get_tree);
1541  
1542  /*
1543   * Setup private BDI for given superblock. It gets automatically cleaned up
1544   * in generic_shutdown_super().
1545   */
1546  int super_setup_bdi_name(struct super_block *sb, char *fmt, ...)
1547  {
1548  	struct backing_dev_info *bdi;
1549  	int err;
1550  	va_list args;
1551  
1552  	bdi = bdi_alloc(NUMA_NO_NODE);
1553  	if (!bdi)
1554  		return -ENOMEM;
1555  
1556  	va_start(args, fmt);
1557  	err = bdi_register_va(bdi, fmt, args);
1558  	va_end(args);
1559  	if (err) {
1560  		bdi_put(bdi);
1561  		return err;
1562  	}
1563  	WARN_ON(sb->s_bdi != &noop_backing_dev_info);
1564  	sb->s_bdi = bdi;
1565  
1566  	return 0;
1567  }
1568  EXPORT_SYMBOL(super_setup_bdi_name);
1569  
1570  /*
1571   * Setup private BDI for given superblock. I gets automatically cleaned up
1572   * in generic_shutdown_super().
1573   */
1574  int super_setup_bdi(struct super_block *sb)
1575  {
1576  	static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
1577  
1578  	return super_setup_bdi_name(sb, "%.28s-%ld", sb->s_type->name,
1579  				    atomic_long_inc_return(&bdi_seq));
1580  }
1581  EXPORT_SYMBOL(super_setup_bdi);
1582  
1583  /**
1584   * sb_wait_write - wait until all writers to given file system finish
1585   * @sb: the super for which we wait
1586   * @level: type of writers we wait for (normal vs page fault)
1587   *
1588   * This function waits until there are no writers of given type to given file
1589   * system.
1590   */
1591  static void sb_wait_write(struct super_block *sb, int level)
1592  {
1593  	percpu_down_write(sb->s_writers.rw_sem + level-1);
1594  }
1595  
1596  /*
1597   * We are going to return to userspace and forget about these locks, the
1598   * ownership goes to the caller of thaw_super() which does unlock().
1599   */
1600  static void lockdep_sb_freeze_release(struct super_block *sb)
1601  {
1602  	int level;
1603  
1604  	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1605  		percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1606  }
1607  
1608  /*
1609   * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
1610   */
1611  static void lockdep_sb_freeze_acquire(struct super_block *sb)
1612  {
1613  	int level;
1614  
1615  	for (level = 0; level < SB_FREEZE_LEVELS; ++level)
1616  		percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1617  }
1618  
1619  static void sb_freeze_unlock(struct super_block *sb)
1620  {
1621  	int level;
1622  
1623  	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1624  		percpu_up_write(sb->s_writers.rw_sem + level);
1625  }
1626  
1627  /**
1628   * freeze_super - lock the filesystem and force it into a consistent state
1629   * @sb: the super to lock
1630   *
1631   * Syncs the super to make sure the filesystem is consistent and calls the fs's
1632   * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1633   * -EBUSY.
1634   *
1635   * During this function, sb->s_writers.frozen goes through these values:
1636   *
1637   * SB_UNFROZEN: File system is normal, all writes progress as usual.
1638   *
1639   * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
1640   * writes should be blocked, though page faults are still allowed. We wait for
1641   * all writes to complete and then proceed to the next stage.
1642   *
1643   * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1644   * but internal fs threads can still modify the filesystem (although they
1645   * should not dirty new pages or inodes), writeback can run etc. After waiting
1646   * for all running page faults we sync the filesystem which will clean all
1647   * dirty pages and inodes (no new dirty pages or inodes can be created when
1648   * sync is running).
1649   *
1650   * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1651   * modification are blocked (e.g. XFS preallocation truncation on inode
1652   * reclaim). This is usually implemented by blocking new transactions for
1653   * filesystems that have them and need this additional guard. After all
1654   * internal writers are finished we call ->freeze_fs() to finish filesystem
1655   * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1656   * mostly auxiliary for filesystems to verify they do not modify frozen fs.
1657   *
1658   * sb->s_writers.frozen is protected by sb->s_umount.
1659   */
1660  int freeze_super(struct super_block *sb)
1661  {
1662  	int ret;
1663  
1664  	atomic_inc(&sb->s_active);
1665  	down_write(&sb->s_umount);
1666  	if (sb->s_writers.frozen != SB_UNFROZEN) {
1667  		deactivate_locked_super(sb);
1668  		return -EBUSY;
1669  	}
1670  
1671  	if (!(sb->s_flags & SB_BORN)) {
1672  		up_write(&sb->s_umount);
1673  		return 0;	/* sic - it's "nothing to do" */
1674  	}
1675  
1676  	if (sb_rdonly(sb)) {
1677  		/* Nothing to do really... */
1678  		sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1679  		up_write(&sb->s_umount);
1680  		return 0;
1681  	}
1682  
1683  	sb->s_writers.frozen = SB_FREEZE_WRITE;
1684  	/* Release s_umount to preserve sb_start_write -> s_umount ordering */
1685  	up_write(&sb->s_umount);
1686  	sb_wait_write(sb, SB_FREEZE_WRITE);
1687  	down_write(&sb->s_umount);
1688  
1689  	/* Now we go and block page faults... */
1690  	sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1691  	sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1692  
1693  	/* All writers are done so after syncing there won't be dirty data */
1694  	sync_filesystem(sb);
1695  
1696  	/* Now wait for internal filesystem counter */
1697  	sb->s_writers.frozen = SB_FREEZE_FS;
1698  	sb_wait_write(sb, SB_FREEZE_FS);
1699  
1700  	if (sb->s_op->freeze_fs) {
1701  		ret = sb->s_op->freeze_fs(sb);
1702  		if (ret) {
1703  			printk(KERN_ERR
1704  				"VFS:Filesystem freeze failed\n");
1705  			sb->s_writers.frozen = SB_UNFROZEN;
1706  			sb_freeze_unlock(sb);
1707  			wake_up(&sb->s_writers.wait_unfrozen);
1708  			deactivate_locked_super(sb);
1709  			return ret;
1710  		}
1711  	}
1712  	/*
1713  	 * For debugging purposes so that fs can warn if it sees write activity
1714  	 * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
1715  	 */
1716  	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1717  	lockdep_sb_freeze_release(sb);
1718  	up_write(&sb->s_umount);
1719  	return 0;
1720  }
1721  EXPORT_SYMBOL(freeze_super);
1722  
1723  static int thaw_super_locked(struct super_block *sb)
1724  {
1725  	int error;
1726  
1727  	if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
1728  		up_write(&sb->s_umount);
1729  		return -EINVAL;
1730  	}
1731  
1732  	if (sb_rdonly(sb)) {
1733  		sb->s_writers.frozen = SB_UNFROZEN;
1734  		goto out;
1735  	}
1736  
1737  	lockdep_sb_freeze_acquire(sb);
1738  
1739  	if (sb->s_op->unfreeze_fs) {
1740  		error = sb->s_op->unfreeze_fs(sb);
1741  		if (error) {
1742  			printk(KERN_ERR
1743  				"VFS:Filesystem thaw failed\n");
1744  			lockdep_sb_freeze_release(sb);
1745  			up_write(&sb->s_umount);
1746  			return error;
1747  		}
1748  	}
1749  
1750  	sb->s_writers.frozen = SB_UNFROZEN;
1751  	sb_freeze_unlock(sb);
1752  out:
1753  	wake_up(&sb->s_writers.wait_unfrozen);
1754  	deactivate_locked_super(sb);
1755  	return 0;
1756  }
1757  
1758  /**
1759   * thaw_super -- unlock filesystem
1760   * @sb: the super to thaw
1761   *
1762   * Unlocks the filesystem and marks it writeable again after freeze_super().
1763   */
1764  int thaw_super(struct super_block *sb)
1765  {
1766  	down_write(&sb->s_umount);
1767  	return thaw_super_locked(sb);
1768  }
1769  EXPORT_SYMBOL(thaw_super);
1770