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