Loading...
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);
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/fscrypt.h>
35#include <linux/fsnotify.h>
36#include <linux/lockdep.h>
37#include <linux/user_namespace.h>
38#include <linux/fs_context.h>
39#include <uapi/linux/mount.h>
40#include "internal.h"
41
42static int thaw_super_locked(struct super_block *sb, enum freeze_holder who);
43
44static LIST_HEAD(super_blocks);
45static DEFINE_SPINLOCK(sb_lock);
46
47static char *sb_writers_name[SB_FREEZE_LEVELS] = {
48 "sb_writers",
49 "sb_pagefaults",
50 "sb_internal",
51};
52
53static inline void __super_lock(struct super_block *sb, bool excl)
54{
55 if (excl)
56 down_write(&sb->s_umount);
57 else
58 down_read(&sb->s_umount);
59}
60
61static inline void super_unlock(struct super_block *sb, bool excl)
62{
63 if (excl)
64 up_write(&sb->s_umount);
65 else
66 up_read(&sb->s_umount);
67}
68
69static inline void __super_lock_excl(struct super_block *sb)
70{
71 __super_lock(sb, true);
72}
73
74static inline void super_unlock_excl(struct super_block *sb)
75{
76 super_unlock(sb, true);
77}
78
79static inline void super_unlock_shared(struct super_block *sb)
80{
81 super_unlock(sb, false);
82}
83
84static bool super_flags(const struct super_block *sb, unsigned int flags)
85{
86 /*
87 * Pairs with smp_store_release() in super_wake() and ensures
88 * that we see @flags after we're woken.
89 */
90 return smp_load_acquire(&sb->s_flags) & flags;
91}
92
93/**
94 * super_lock - wait for superblock to become ready and lock it
95 * @sb: superblock to wait for
96 * @excl: whether exclusive access is required
97 *
98 * If the superblock has neither passed through vfs_get_tree() or
99 * generic_shutdown_super() yet wait for it to happen. Either superblock
100 * creation will succeed and SB_BORN is set by vfs_get_tree() or we're
101 * woken and we'll see SB_DYING.
102 *
103 * The caller must have acquired a temporary reference on @sb->s_count.
104 *
105 * Return: The function returns true if SB_BORN was set and with
106 * s_umount held. The function returns false if SB_DYING was
107 * set and without s_umount held.
108 */
109static __must_check bool super_lock(struct super_block *sb, bool excl)
110{
111 lockdep_assert_not_held(&sb->s_umount);
112
113 /* wait until the superblock is ready or dying */
114 wait_var_event(&sb->s_flags, super_flags(sb, SB_BORN | SB_DYING));
115
116 /* Don't pointlessly acquire s_umount. */
117 if (super_flags(sb, SB_DYING))
118 return false;
119
120 __super_lock(sb, excl);
121
122 /*
123 * Has gone through generic_shutdown_super() in the meantime.
124 * @sb->s_root is NULL and @sb->s_active is 0. No one needs to
125 * grab a reference to this. Tell them so.
126 */
127 if (sb->s_flags & SB_DYING) {
128 super_unlock(sb, excl);
129 return false;
130 }
131
132 WARN_ON_ONCE(!(sb->s_flags & SB_BORN));
133 return true;
134}
135
136/* wait and try to acquire read-side of @sb->s_umount */
137static inline bool super_lock_shared(struct super_block *sb)
138{
139 return super_lock(sb, false);
140}
141
142/* wait and try to acquire write-side of @sb->s_umount */
143static inline bool super_lock_excl(struct super_block *sb)
144{
145 return super_lock(sb, true);
146}
147
148/* wake waiters */
149#define SUPER_WAKE_FLAGS (SB_BORN | SB_DYING | SB_DEAD)
150static void super_wake(struct super_block *sb, unsigned int flag)
151{
152 WARN_ON_ONCE((flag & ~SUPER_WAKE_FLAGS));
153 WARN_ON_ONCE(hweight32(flag & SUPER_WAKE_FLAGS) > 1);
154
155 /*
156 * Pairs with smp_load_acquire() in super_lock() to make sure
157 * all initializations in the superblock are seen by the user
158 * seeing SB_BORN sent.
159 */
160 smp_store_release(&sb->s_flags, sb->s_flags | flag);
161 /*
162 * Pairs with the barrier in prepare_to_wait_event() to make sure
163 * ___wait_var_event() either sees SB_BORN set or
164 * waitqueue_active() check in wake_up_var() sees the waiter.
165 */
166 smp_mb();
167 wake_up_var(&sb->s_flags);
168}
169
170/*
171 * One thing we have to be careful of with a per-sb shrinker is that we don't
172 * drop the last active reference to the superblock from within the shrinker.
173 * If that happens we could trigger unregistering the shrinker from within the
174 * shrinker path and that leads to deadlock on the shrinker_mutex. Hence we
175 * take a passive reference to the superblock to avoid this from occurring.
176 */
177static unsigned long super_cache_scan(struct shrinker *shrink,
178 struct shrink_control *sc)
179{
180 struct super_block *sb;
181 long fs_objects = 0;
182 long total_objects;
183 long freed = 0;
184 long dentries;
185 long inodes;
186
187 sb = shrink->private_data;
188
189 /*
190 * Deadlock avoidance. We may hold various FS locks, and we don't want
191 * to recurse into the FS that called us in clear_inode() and friends..
192 */
193 if (!(sc->gfp_mask & __GFP_FS))
194 return SHRINK_STOP;
195
196 if (!super_trylock_shared(sb))
197 return SHRINK_STOP;
198
199 if (sb->s_op->nr_cached_objects)
200 fs_objects = sb->s_op->nr_cached_objects(sb, sc);
201
202 inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
203 dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc);
204 total_objects = dentries + inodes + fs_objects + 1;
205 if (!total_objects)
206 total_objects = 1;
207
208 /* proportion the scan between the caches */
209 dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);
210 inodes = mult_frac(sc->nr_to_scan, inodes, total_objects);
211 fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
212
213 /*
214 * prune the dcache first as the icache is pinned by it, then
215 * prune the icache, followed by the filesystem specific caches
216 *
217 * Ensure that we always scan at least one object - memcg kmem
218 * accounting uses this to fully empty the caches.
219 */
220 sc->nr_to_scan = dentries + 1;
221 freed = prune_dcache_sb(sb, sc);
222 sc->nr_to_scan = inodes + 1;
223 freed += prune_icache_sb(sb, sc);
224
225 if (fs_objects) {
226 sc->nr_to_scan = fs_objects + 1;
227 freed += sb->s_op->free_cached_objects(sb, sc);
228 }
229
230 super_unlock_shared(sb);
231 return freed;
232}
233
234static unsigned long super_cache_count(struct shrinker *shrink,
235 struct shrink_control *sc)
236{
237 struct super_block *sb;
238 long total_objects = 0;
239
240 sb = shrink->private_data;
241
242 /*
243 * We don't call super_trylock_shared() here as it is a scalability
244 * bottleneck, so we're exposed to partial setup state. The shrinker
245 * rwsem does not protect filesystem operations backing
246 * list_lru_shrink_count() or s_op->nr_cached_objects(). Counts can
247 * change between super_cache_count and super_cache_scan, so we really
248 * don't need locks here.
249 *
250 * However, if we are currently mounting the superblock, the underlying
251 * filesystem might be in a state of partial construction and hence it
252 * is dangerous to access it. super_trylock_shared() uses a SB_BORN check
253 * to avoid this situation, so do the same here. The memory barrier is
254 * matched with the one in mount_fs() as we don't hold locks here.
255 */
256 if (!(sb->s_flags & SB_BORN))
257 return 0;
258 smp_rmb();
259
260 if (sb->s_op && sb->s_op->nr_cached_objects)
261 total_objects = sb->s_op->nr_cached_objects(sb, sc);
262
263 total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
264 total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
265
266 if (!total_objects)
267 return SHRINK_EMPTY;
268
269 total_objects = vfs_pressure_ratio(total_objects);
270 return total_objects;
271}
272
273static void destroy_super_work(struct work_struct *work)
274{
275 struct super_block *s = container_of(work, struct super_block,
276 destroy_work);
277 security_sb_free(s);
278 put_user_ns(s->s_user_ns);
279 kfree(s->s_subtype);
280 for (int i = 0; i < SB_FREEZE_LEVELS; i++)
281 percpu_free_rwsem(&s->s_writers.rw_sem[i]);
282 kfree(s);
283}
284
285static void destroy_super_rcu(struct rcu_head *head)
286{
287 struct super_block *s = container_of(head, struct super_block, rcu);
288 INIT_WORK(&s->destroy_work, destroy_super_work);
289 schedule_work(&s->destroy_work);
290}
291
292/* Free a superblock that has never been seen by anyone */
293static void destroy_unused_super(struct super_block *s)
294{
295 if (!s)
296 return;
297 super_unlock_excl(s);
298 list_lru_destroy(&s->s_dentry_lru);
299 list_lru_destroy(&s->s_inode_lru);
300 shrinker_free(s->s_shrink);
301 /* no delays needed */
302 destroy_super_work(&s->destroy_work);
303}
304
305/**
306 * alloc_super - create new superblock
307 * @type: filesystem type superblock should belong to
308 * @flags: the mount flags
309 * @user_ns: User namespace for the super_block
310 *
311 * Allocates and initializes a new &struct super_block. alloc_super()
312 * returns a pointer new superblock or %NULL if allocation had failed.
313 */
314static struct super_block *alloc_super(struct file_system_type *type, int flags,
315 struct user_namespace *user_ns)
316{
317 struct super_block *s = kzalloc(sizeof(struct super_block), GFP_KERNEL);
318 static const struct super_operations default_op;
319 int i;
320
321 if (!s)
322 return NULL;
323
324 INIT_LIST_HEAD(&s->s_mounts);
325 s->s_user_ns = get_user_ns(user_ns);
326 init_rwsem(&s->s_umount);
327 lockdep_set_class(&s->s_umount, &type->s_umount_key);
328 /*
329 * sget() can have s_umount recursion.
330 *
331 * When it cannot find a suitable sb, it allocates a new
332 * one (this one), and tries again to find a suitable old
333 * one.
334 *
335 * In case that succeeds, it will acquire the s_umount
336 * lock of the old one. Since these are clearly distrinct
337 * locks, and this object isn't exposed yet, there's no
338 * risk of deadlocks.
339 *
340 * Annotate this by putting this lock in a different
341 * subclass.
342 */
343 down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
344
345 if (security_sb_alloc(s))
346 goto fail;
347
348 for (i = 0; i < SB_FREEZE_LEVELS; i++) {
349 if (__percpu_init_rwsem(&s->s_writers.rw_sem[i],
350 sb_writers_name[i],
351 &type->s_writers_key[i]))
352 goto fail;
353 }
354 s->s_bdi = &noop_backing_dev_info;
355 s->s_flags = flags;
356 if (s->s_user_ns != &init_user_ns)
357 s->s_iflags |= SB_I_NODEV;
358 INIT_HLIST_NODE(&s->s_instances);
359 INIT_HLIST_BL_HEAD(&s->s_roots);
360 mutex_init(&s->s_sync_lock);
361 INIT_LIST_HEAD(&s->s_inodes);
362 spin_lock_init(&s->s_inode_list_lock);
363 INIT_LIST_HEAD(&s->s_inodes_wb);
364 spin_lock_init(&s->s_inode_wblist_lock);
365
366 s->s_count = 1;
367 atomic_set(&s->s_active, 1);
368 mutex_init(&s->s_vfs_rename_mutex);
369 lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
370 init_rwsem(&s->s_dquot.dqio_sem);
371 s->s_maxbytes = MAX_NON_LFS;
372 s->s_op = &default_op;
373 s->s_time_gran = 1000000000;
374 s->s_time_min = TIME64_MIN;
375 s->s_time_max = TIME64_MAX;
376
377 s->s_shrink = shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
378 "sb-%s", type->name);
379 if (!s->s_shrink)
380 goto fail;
381
382 s->s_shrink->scan_objects = super_cache_scan;
383 s->s_shrink->count_objects = super_cache_count;
384 s->s_shrink->batch = 1024;
385 s->s_shrink->private_data = s;
386
387 if (list_lru_init_memcg(&s->s_dentry_lru, s->s_shrink))
388 goto fail;
389 if (list_lru_init_memcg(&s->s_inode_lru, s->s_shrink))
390 goto fail;
391 return s;
392
393fail:
394 destroy_unused_super(s);
395 return NULL;
396}
397
398/* Superblock refcounting */
399
400/*
401 * Drop a superblock's refcount. The caller must hold sb_lock.
402 */
403static void __put_super(struct super_block *s)
404{
405 if (!--s->s_count) {
406 list_del_init(&s->s_list);
407 WARN_ON(s->s_dentry_lru.node);
408 WARN_ON(s->s_inode_lru.node);
409 WARN_ON(!list_empty(&s->s_mounts));
410 call_rcu(&s->rcu, destroy_super_rcu);
411 }
412}
413
414/**
415 * put_super - drop a temporary reference to superblock
416 * @sb: superblock in question
417 *
418 * Drops a temporary reference, frees superblock if there's no
419 * references left.
420 */
421void put_super(struct super_block *sb)
422{
423 spin_lock(&sb_lock);
424 __put_super(sb);
425 spin_unlock(&sb_lock);
426}
427
428static void kill_super_notify(struct super_block *sb)
429{
430 lockdep_assert_not_held(&sb->s_umount);
431
432 /* already notified earlier */
433 if (sb->s_flags & SB_DEAD)
434 return;
435
436 /*
437 * Remove it from @fs_supers so it isn't found by new
438 * sget{_fc}() walkers anymore. Any concurrent mounter still
439 * managing to grab a temporary reference is guaranteed to
440 * already see SB_DYING and will wait until we notify them about
441 * SB_DEAD.
442 */
443 spin_lock(&sb_lock);
444 hlist_del_init(&sb->s_instances);
445 spin_unlock(&sb_lock);
446
447 /*
448 * Let concurrent mounts know that this thing is really dead.
449 * We don't need @sb->s_umount here as every concurrent caller
450 * will see SB_DYING and either discard the superblock or wait
451 * for SB_DEAD.
452 */
453 super_wake(sb, SB_DEAD);
454}
455
456/**
457 * deactivate_locked_super - drop an active reference to superblock
458 * @s: superblock to deactivate
459 *
460 * Drops an active reference to superblock, converting it into a temporary
461 * one if there is no other active references left. In that case we
462 * tell fs driver to shut it down and drop the temporary reference we
463 * had just acquired.
464 *
465 * Caller holds exclusive lock on superblock; that lock is released.
466 */
467void deactivate_locked_super(struct super_block *s)
468{
469 struct file_system_type *fs = s->s_type;
470 if (atomic_dec_and_test(&s->s_active)) {
471 shrinker_free(s->s_shrink);
472 fs->kill_sb(s);
473
474 kill_super_notify(s);
475
476 /*
477 * Since list_lru_destroy() may sleep, we cannot call it from
478 * put_super(), where we hold the sb_lock. Therefore we destroy
479 * the lru lists right now.
480 */
481 list_lru_destroy(&s->s_dentry_lru);
482 list_lru_destroy(&s->s_inode_lru);
483
484 put_filesystem(fs);
485 put_super(s);
486 } else {
487 super_unlock_excl(s);
488 }
489}
490
491EXPORT_SYMBOL(deactivate_locked_super);
492
493/**
494 * deactivate_super - drop an active reference to superblock
495 * @s: superblock to deactivate
496 *
497 * Variant of deactivate_locked_super(), except that superblock is *not*
498 * locked by caller. If we are going to drop the final active reference,
499 * lock will be acquired prior to that.
500 */
501void deactivate_super(struct super_block *s)
502{
503 if (!atomic_add_unless(&s->s_active, -1, 1)) {
504 __super_lock_excl(s);
505 deactivate_locked_super(s);
506 }
507}
508
509EXPORT_SYMBOL(deactivate_super);
510
511/**
512 * grab_super - acquire an active reference to a superblock
513 * @sb: superblock to acquire
514 *
515 * Acquire a temporary reference on a superblock and try to trade it for
516 * an active reference. This is used in sget{_fc}() to wait for a
517 * superblock to either become SB_BORN or for it to pass through
518 * sb->kill() and be marked as SB_DEAD.
519 *
520 * Return: This returns true if an active reference could be acquired,
521 * false if not.
522 */
523static bool grab_super(struct super_block *sb)
524{
525 bool locked;
526
527 sb->s_count++;
528 spin_unlock(&sb_lock);
529 locked = super_lock_excl(sb);
530 if (locked) {
531 if (atomic_inc_not_zero(&sb->s_active)) {
532 put_super(sb);
533 return true;
534 }
535 super_unlock_excl(sb);
536 }
537 wait_var_event(&sb->s_flags, super_flags(sb, SB_DEAD));
538 put_super(sb);
539 return false;
540}
541
542/*
543 * super_trylock_shared - try to grab ->s_umount shared
544 * @sb: reference we are trying to grab
545 *
546 * Try to prevent fs shutdown. This is used in places where we
547 * cannot take an active reference but we need to ensure that the
548 * filesystem is not shut down while we are working on it. It returns
549 * false if we cannot acquire s_umount or if we lose the race and
550 * filesystem already got into shutdown, and returns true with the s_umount
551 * lock held in read mode in case of success. On successful return,
552 * the caller must drop the s_umount lock when done.
553 *
554 * Note that unlike get_super() et.al. this one does *not* bump ->s_count.
555 * The reason why it's safe is that we are OK with doing trylock instead
556 * of down_read(). There's a couple of places that are OK with that, but
557 * it's very much not a general-purpose interface.
558 */
559bool super_trylock_shared(struct super_block *sb)
560{
561 if (down_read_trylock(&sb->s_umount)) {
562 if (!(sb->s_flags & SB_DYING) && sb->s_root &&
563 (sb->s_flags & SB_BORN))
564 return true;
565 super_unlock_shared(sb);
566 }
567
568 return false;
569}
570
571/**
572 * retire_super - prevents superblock from being reused
573 * @sb: superblock to retire
574 *
575 * The function marks superblock to be ignored in superblock test, which
576 * prevents it from being reused for any new mounts. If the superblock has
577 * a private bdi, it also unregisters it, but doesn't reduce the refcount
578 * of the superblock to prevent potential races. The refcount is reduced
579 * by generic_shutdown_super(). The function can not be called
580 * concurrently with generic_shutdown_super(). It is safe to call the
581 * function multiple times, subsequent calls have no effect.
582 *
583 * The marker will affect the re-use only for block-device-based
584 * superblocks. Other superblocks will still get marked if this function
585 * is used, but that will not affect their reusability.
586 */
587void retire_super(struct super_block *sb)
588{
589 WARN_ON(!sb->s_bdev);
590 __super_lock_excl(sb);
591 if (sb->s_iflags & SB_I_PERSB_BDI) {
592 bdi_unregister(sb->s_bdi);
593 sb->s_iflags &= ~SB_I_PERSB_BDI;
594 }
595 sb->s_iflags |= SB_I_RETIRED;
596 super_unlock_excl(sb);
597}
598EXPORT_SYMBOL(retire_super);
599
600/**
601 * generic_shutdown_super - common helper for ->kill_sb()
602 * @sb: superblock to kill
603 *
604 * generic_shutdown_super() does all fs-independent work on superblock
605 * shutdown. Typical ->kill_sb() should pick all fs-specific objects
606 * that need destruction out of superblock, call generic_shutdown_super()
607 * and release aforementioned objects. Note: dentries and inodes _are_
608 * taken care of and do not need specific handling.
609 *
610 * Upon calling this function, the filesystem may no longer alter or
611 * rearrange the set of dentries belonging to this super_block, nor may it
612 * change the attachments of dentries to inodes.
613 */
614void generic_shutdown_super(struct super_block *sb)
615{
616 const struct super_operations *sop = sb->s_op;
617
618 if (sb->s_root) {
619 shrink_dcache_for_umount(sb);
620 sync_filesystem(sb);
621 sb->s_flags &= ~SB_ACTIVE;
622
623 cgroup_writeback_umount();
624
625 /* Evict all inodes with zero refcount. */
626 evict_inodes(sb);
627
628 /*
629 * Clean up and evict any inodes that still have references due
630 * to fsnotify or the security policy.
631 */
632 fsnotify_sb_delete(sb);
633 security_sb_delete(sb);
634
635 if (sb->s_dio_done_wq) {
636 destroy_workqueue(sb->s_dio_done_wq);
637 sb->s_dio_done_wq = NULL;
638 }
639
640 if (sop->put_super)
641 sop->put_super(sb);
642
643 /*
644 * Now that all potentially-encrypted inodes have been evicted,
645 * the fscrypt keyring can be destroyed.
646 */
647 fscrypt_destroy_keyring(sb);
648
649 if (CHECK_DATA_CORRUPTION(!list_empty(&sb->s_inodes),
650 "VFS: Busy inodes after unmount of %s (%s)",
651 sb->s_id, sb->s_type->name)) {
652 /*
653 * Adding a proper bailout path here would be hard, but
654 * we can at least make it more likely that a later
655 * iput_final() or such crashes cleanly.
656 */
657 struct inode *inode;
658
659 spin_lock(&sb->s_inode_list_lock);
660 list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
661 inode->i_op = VFS_PTR_POISON;
662 inode->i_sb = VFS_PTR_POISON;
663 inode->i_mapping = VFS_PTR_POISON;
664 }
665 spin_unlock(&sb->s_inode_list_lock);
666 }
667 }
668 /*
669 * Broadcast to everyone that grabbed a temporary reference to this
670 * superblock before we removed it from @fs_supers that the superblock
671 * is dying. Every walker of @fs_supers outside of sget{_fc}() will now
672 * discard this superblock and treat it as dead.
673 *
674 * We leave the superblock on @fs_supers so it can be found by
675 * sget{_fc}() until we passed sb->kill_sb().
676 */
677 super_wake(sb, SB_DYING);
678 super_unlock_excl(sb);
679 if (sb->s_bdi != &noop_backing_dev_info) {
680 if (sb->s_iflags & SB_I_PERSB_BDI)
681 bdi_unregister(sb->s_bdi);
682 bdi_put(sb->s_bdi);
683 sb->s_bdi = &noop_backing_dev_info;
684 }
685}
686
687EXPORT_SYMBOL(generic_shutdown_super);
688
689bool mount_capable(struct fs_context *fc)
690{
691 if (!(fc->fs_type->fs_flags & FS_USERNS_MOUNT))
692 return capable(CAP_SYS_ADMIN);
693 else
694 return ns_capable(fc->user_ns, CAP_SYS_ADMIN);
695}
696
697/**
698 * sget_fc - Find or create a superblock
699 * @fc: Filesystem context.
700 * @test: Comparison callback
701 * @set: Setup callback
702 *
703 * Create a new superblock or find an existing one.
704 *
705 * The @test callback is used to find a matching existing superblock.
706 * Whether or not the requested parameters in @fc are taken into account
707 * is specific to the @test callback that is used. They may even be
708 * completely ignored.
709 *
710 * If an extant superblock is matched, it will be returned unless:
711 *
712 * (1) the namespace the filesystem context @fc and the extant
713 * superblock's namespace differ
714 *
715 * (2) the filesystem context @fc has requested that reusing an extant
716 * superblock is not allowed
717 *
718 * In both cases EBUSY will be returned.
719 *
720 * If no match is made, a new superblock will be allocated and basic
721 * initialisation will be performed (s_type, s_fs_info and s_id will be
722 * set and the @set callback will be invoked), the superblock will be
723 * published and it will be returned in a partially constructed state
724 * with SB_BORN and SB_ACTIVE as yet unset.
725 *
726 * Return: On success, an extant or newly created superblock is
727 * returned. On failure an error pointer is returned.
728 */
729struct super_block *sget_fc(struct fs_context *fc,
730 int (*test)(struct super_block *, struct fs_context *),
731 int (*set)(struct super_block *, struct fs_context *))
732{
733 struct super_block *s = NULL;
734 struct super_block *old;
735 struct user_namespace *user_ns = fc->global ? &init_user_ns : fc->user_ns;
736 int err;
737
738retry:
739 spin_lock(&sb_lock);
740 if (test) {
741 hlist_for_each_entry(old, &fc->fs_type->fs_supers, s_instances) {
742 if (test(old, fc))
743 goto share_extant_sb;
744 }
745 }
746 if (!s) {
747 spin_unlock(&sb_lock);
748 s = alloc_super(fc->fs_type, fc->sb_flags, user_ns);
749 if (!s)
750 return ERR_PTR(-ENOMEM);
751 goto retry;
752 }
753
754 s->s_fs_info = fc->s_fs_info;
755 err = set(s, fc);
756 if (err) {
757 s->s_fs_info = NULL;
758 spin_unlock(&sb_lock);
759 destroy_unused_super(s);
760 return ERR_PTR(err);
761 }
762 fc->s_fs_info = NULL;
763 s->s_type = fc->fs_type;
764 s->s_iflags |= fc->s_iflags;
765 strscpy(s->s_id, s->s_type->name, sizeof(s->s_id));
766 /*
767 * Make the superblock visible on @super_blocks and @fs_supers.
768 * It's in a nascent state and users should wait on SB_BORN or
769 * SB_DYING to be set.
770 */
771 list_add_tail(&s->s_list, &super_blocks);
772 hlist_add_head(&s->s_instances, &s->s_type->fs_supers);
773 spin_unlock(&sb_lock);
774 get_filesystem(s->s_type);
775 shrinker_register(s->s_shrink);
776 return s;
777
778share_extant_sb:
779 if (user_ns != old->s_user_ns || fc->exclusive) {
780 spin_unlock(&sb_lock);
781 destroy_unused_super(s);
782 if (fc->exclusive)
783 warnfc(fc, "reusing existing filesystem not allowed");
784 else
785 warnfc(fc, "reusing existing filesystem in another namespace not allowed");
786 return ERR_PTR(-EBUSY);
787 }
788 if (!grab_super(old))
789 goto retry;
790 destroy_unused_super(s);
791 return old;
792}
793EXPORT_SYMBOL(sget_fc);
794
795/**
796 * sget - find or create a superblock
797 * @type: filesystem type superblock should belong to
798 * @test: comparison callback
799 * @set: setup callback
800 * @flags: mount flags
801 * @data: argument to each of them
802 */
803struct super_block *sget(struct file_system_type *type,
804 int (*test)(struct super_block *,void *),
805 int (*set)(struct super_block *,void *),
806 int flags,
807 void *data)
808{
809 struct user_namespace *user_ns = current_user_ns();
810 struct super_block *s = NULL;
811 struct super_block *old;
812 int err;
813
814 /* We don't yet pass the user namespace of the parent
815 * mount through to here so always use &init_user_ns
816 * until that changes.
817 */
818 if (flags & SB_SUBMOUNT)
819 user_ns = &init_user_ns;
820
821retry:
822 spin_lock(&sb_lock);
823 if (test) {
824 hlist_for_each_entry(old, &type->fs_supers, s_instances) {
825 if (!test(old, data))
826 continue;
827 if (user_ns != old->s_user_ns) {
828 spin_unlock(&sb_lock);
829 destroy_unused_super(s);
830 return ERR_PTR(-EBUSY);
831 }
832 if (!grab_super(old))
833 goto retry;
834 destroy_unused_super(s);
835 return old;
836 }
837 }
838 if (!s) {
839 spin_unlock(&sb_lock);
840 s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
841 if (!s)
842 return ERR_PTR(-ENOMEM);
843 goto retry;
844 }
845
846 err = set(s, data);
847 if (err) {
848 spin_unlock(&sb_lock);
849 destroy_unused_super(s);
850 return ERR_PTR(err);
851 }
852 s->s_type = type;
853 strscpy(s->s_id, type->name, sizeof(s->s_id));
854 list_add_tail(&s->s_list, &super_blocks);
855 hlist_add_head(&s->s_instances, &type->fs_supers);
856 spin_unlock(&sb_lock);
857 get_filesystem(type);
858 shrinker_register(s->s_shrink);
859 return s;
860}
861EXPORT_SYMBOL(sget);
862
863void drop_super(struct super_block *sb)
864{
865 super_unlock_shared(sb);
866 put_super(sb);
867}
868
869EXPORT_SYMBOL(drop_super);
870
871void drop_super_exclusive(struct super_block *sb)
872{
873 super_unlock_excl(sb);
874 put_super(sb);
875}
876EXPORT_SYMBOL(drop_super_exclusive);
877
878static void __iterate_supers(void (*f)(struct super_block *))
879{
880 struct super_block *sb, *p = NULL;
881
882 spin_lock(&sb_lock);
883 list_for_each_entry(sb, &super_blocks, s_list) {
884 if (super_flags(sb, SB_DYING))
885 continue;
886 sb->s_count++;
887 spin_unlock(&sb_lock);
888
889 f(sb);
890
891 spin_lock(&sb_lock);
892 if (p)
893 __put_super(p);
894 p = sb;
895 }
896 if (p)
897 __put_super(p);
898 spin_unlock(&sb_lock);
899}
900/**
901 * iterate_supers - call function for all active superblocks
902 * @f: function to call
903 * @arg: argument to pass to it
904 *
905 * Scans the superblock list and calls given function, passing it
906 * locked superblock and given argument.
907 */
908void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
909{
910 struct super_block *sb, *p = NULL;
911
912 spin_lock(&sb_lock);
913 list_for_each_entry(sb, &super_blocks, s_list) {
914 bool locked;
915
916 sb->s_count++;
917 spin_unlock(&sb_lock);
918
919 locked = super_lock_shared(sb);
920 if (locked) {
921 if (sb->s_root)
922 f(sb, arg);
923 super_unlock_shared(sb);
924 }
925
926 spin_lock(&sb_lock);
927 if (p)
928 __put_super(p);
929 p = sb;
930 }
931 if (p)
932 __put_super(p);
933 spin_unlock(&sb_lock);
934}
935
936/**
937 * iterate_supers_type - call function for superblocks of given type
938 * @type: fs type
939 * @f: function to call
940 * @arg: argument to pass to it
941 *
942 * Scans the superblock list and calls given function, passing it
943 * locked superblock and given argument.
944 */
945void iterate_supers_type(struct file_system_type *type,
946 void (*f)(struct super_block *, void *), void *arg)
947{
948 struct super_block *sb, *p = NULL;
949
950 spin_lock(&sb_lock);
951 hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
952 bool locked;
953
954 sb->s_count++;
955 spin_unlock(&sb_lock);
956
957 locked = super_lock_shared(sb);
958 if (locked) {
959 if (sb->s_root)
960 f(sb, arg);
961 super_unlock_shared(sb);
962 }
963
964 spin_lock(&sb_lock);
965 if (p)
966 __put_super(p);
967 p = sb;
968 }
969 if (p)
970 __put_super(p);
971 spin_unlock(&sb_lock);
972}
973
974EXPORT_SYMBOL(iterate_supers_type);
975
976struct super_block *user_get_super(dev_t dev, bool excl)
977{
978 struct super_block *sb;
979
980 spin_lock(&sb_lock);
981 list_for_each_entry(sb, &super_blocks, s_list) {
982 if (sb->s_dev == dev) {
983 bool locked;
984
985 sb->s_count++;
986 spin_unlock(&sb_lock);
987 /* still alive? */
988 locked = super_lock(sb, excl);
989 if (locked) {
990 if (sb->s_root)
991 return sb;
992 super_unlock(sb, excl);
993 }
994 /* nope, got unmounted */
995 spin_lock(&sb_lock);
996 __put_super(sb);
997 break;
998 }
999 }
1000 spin_unlock(&sb_lock);
1001 return NULL;
1002}
1003
1004/**
1005 * reconfigure_super - asks filesystem to change superblock parameters
1006 * @fc: The superblock and configuration
1007 *
1008 * Alters the configuration parameters of a live superblock.
1009 */
1010int reconfigure_super(struct fs_context *fc)
1011{
1012 struct super_block *sb = fc->root->d_sb;
1013 int retval;
1014 bool remount_ro = false;
1015 bool remount_rw = false;
1016 bool force = fc->sb_flags & SB_FORCE;
1017
1018 if (fc->sb_flags_mask & ~MS_RMT_MASK)
1019 return -EINVAL;
1020 if (sb->s_writers.frozen != SB_UNFROZEN)
1021 return -EBUSY;
1022
1023 retval = security_sb_remount(sb, fc->security);
1024 if (retval)
1025 return retval;
1026
1027 if (fc->sb_flags_mask & SB_RDONLY) {
1028#ifdef CONFIG_BLOCK
1029 if (!(fc->sb_flags & SB_RDONLY) && sb->s_bdev &&
1030 bdev_read_only(sb->s_bdev))
1031 return -EACCES;
1032#endif
1033 remount_rw = !(fc->sb_flags & SB_RDONLY) && sb_rdonly(sb);
1034 remount_ro = (fc->sb_flags & SB_RDONLY) && !sb_rdonly(sb);
1035 }
1036
1037 if (remount_ro) {
1038 if (!hlist_empty(&sb->s_pins)) {
1039 super_unlock_excl(sb);
1040 group_pin_kill(&sb->s_pins);
1041 __super_lock_excl(sb);
1042 if (!sb->s_root)
1043 return 0;
1044 if (sb->s_writers.frozen != SB_UNFROZEN)
1045 return -EBUSY;
1046 remount_ro = !sb_rdonly(sb);
1047 }
1048 }
1049 shrink_dcache_sb(sb);
1050
1051 /* If we are reconfiguring to RDONLY and current sb is read/write,
1052 * make sure there are no files open for writing.
1053 */
1054 if (remount_ro) {
1055 if (force) {
1056 sb_start_ro_state_change(sb);
1057 } else {
1058 retval = sb_prepare_remount_readonly(sb);
1059 if (retval)
1060 return retval;
1061 }
1062 } else if (remount_rw) {
1063 /*
1064 * Protect filesystem's reconfigure code from writes from
1065 * userspace until reconfigure finishes.
1066 */
1067 sb_start_ro_state_change(sb);
1068 }
1069
1070 if (fc->ops->reconfigure) {
1071 retval = fc->ops->reconfigure(fc);
1072 if (retval) {
1073 if (!force)
1074 goto cancel_readonly;
1075 /* If forced remount, go ahead despite any errors */
1076 WARN(1, "forced remount of a %s fs returned %i\n",
1077 sb->s_type->name, retval);
1078 }
1079 }
1080
1081 WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) |
1082 (fc->sb_flags & fc->sb_flags_mask)));
1083 sb_end_ro_state_change(sb);
1084
1085 /*
1086 * Some filesystems modify their metadata via some other path than the
1087 * bdev buffer cache (eg. use a private mapping, or directories in
1088 * pagecache, etc). Also file data modifications go via their own
1089 * mappings. So If we try to mount readonly then copy the filesystem
1090 * from bdev, we could get stale data, so invalidate it to give a best
1091 * effort at coherency.
1092 */
1093 if (remount_ro && sb->s_bdev)
1094 invalidate_bdev(sb->s_bdev);
1095 return 0;
1096
1097cancel_readonly:
1098 sb_end_ro_state_change(sb);
1099 return retval;
1100}
1101
1102static void do_emergency_remount_callback(struct super_block *sb)
1103{
1104 bool locked = super_lock_excl(sb);
1105
1106 if (locked && sb->s_root && sb->s_bdev && !sb_rdonly(sb)) {
1107 struct fs_context *fc;
1108
1109 fc = fs_context_for_reconfigure(sb->s_root,
1110 SB_RDONLY | SB_FORCE, SB_RDONLY);
1111 if (!IS_ERR(fc)) {
1112 if (parse_monolithic_mount_data(fc, NULL) == 0)
1113 (void)reconfigure_super(fc);
1114 put_fs_context(fc);
1115 }
1116 }
1117 if (locked)
1118 super_unlock_excl(sb);
1119}
1120
1121static void do_emergency_remount(struct work_struct *work)
1122{
1123 __iterate_supers(do_emergency_remount_callback);
1124 kfree(work);
1125 printk("Emergency Remount complete\n");
1126}
1127
1128void emergency_remount(void)
1129{
1130 struct work_struct *work;
1131
1132 work = kmalloc(sizeof(*work), GFP_ATOMIC);
1133 if (work) {
1134 INIT_WORK(work, do_emergency_remount);
1135 schedule_work(work);
1136 }
1137}
1138
1139static void do_thaw_all_callback(struct super_block *sb)
1140{
1141 bool locked = super_lock_excl(sb);
1142
1143 if (locked && sb->s_root) {
1144 if (IS_ENABLED(CONFIG_BLOCK))
1145 while (sb->s_bdev && !bdev_thaw(sb->s_bdev))
1146 pr_warn("Emergency Thaw on %pg\n", sb->s_bdev);
1147 thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE);
1148 return;
1149 }
1150 if (locked)
1151 super_unlock_excl(sb);
1152}
1153
1154static void do_thaw_all(struct work_struct *work)
1155{
1156 __iterate_supers(do_thaw_all_callback);
1157 kfree(work);
1158 printk(KERN_WARNING "Emergency Thaw complete\n");
1159}
1160
1161/**
1162 * emergency_thaw_all -- forcibly thaw every frozen filesystem
1163 *
1164 * Used for emergency unfreeze of all filesystems via SysRq
1165 */
1166void emergency_thaw_all(void)
1167{
1168 struct work_struct *work;
1169
1170 work = kmalloc(sizeof(*work), GFP_ATOMIC);
1171 if (work) {
1172 INIT_WORK(work, do_thaw_all);
1173 schedule_work(work);
1174 }
1175}
1176
1177static DEFINE_IDA(unnamed_dev_ida);
1178
1179/**
1180 * get_anon_bdev - Allocate a block device for filesystems which don't have one.
1181 * @p: Pointer to a dev_t.
1182 *
1183 * Filesystems which don't use real block devices can call this function
1184 * to allocate a virtual block device.
1185 *
1186 * Context: Any context. Frequently called while holding sb_lock.
1187 * Return: 0 on success, -EMFILE if there are no anonymous bdevs left
1188 * or -ENOMEM if memory allocation failed.
1189 */
1190int get_anon_bdev(dev_t *p)
1191{
1192 int dev;
1193
1194 /*
1195 * Many userspace utilities consider an FSID of 0 invalid.
1196 * Always return at least 1 from get_anon_bdev.
1197 */
1198 dev = ida_alloc_range(&unnamed_dev_ida, 1, (1 << MINORBITS) - 1,
1199 GFP_ATOMIC);
1200 if (dev == -ENOSPC)
1201 dev = -EMFILE;
1202 if (dev < 0)
1203 return dev;
1204
1205 *p = MKDEV(0, dev);
1206 return 0;
1207}
1208EXPORT_SYMBOL(get_anon_bdev);
1209
1210void free_anon_bdev(dev_t dev)
1211{
1212 ida_free(&unnamed_dev_ida, MINOR(dev));
1213}
1214EXPORT_SYMBOL(free_anon_bdev);
1215
1216int set_anon_super(struct super_block *s, void *data)
1217{
1218 return get_anon_bdev(&s->s_dev);
1219}
1220EXPORT_SYMBOL(set_anon_super);
1221
1222void kill_anon_super(struct super_block *sb)
1223{
1224 dev_t dev = sb->s_dev;
1225 generic_shutdown_super(sb);
1226 kill_super_notify(sb);
1227 free_anon_bdev(dev);
1228}
1229EXPORT_SYMBOL(kill_anon_super);
1230
1231void kill_litter_super(struct super_block *sb)
1232{
1233 if (sb->s_root)
1234 d_genocide(sb->s_root);
1235 kill_anon_super(sb);
1236}
1237EXPORT_SYMBOL(kill_litter_super);
1238
1239int set_anon_super_fc(struct super_block *sb, struct fs_context *fc)
1240{
1241 return set_anon_super(sb, NULL);
1242}
1243EXPORT_SYMBOL(set_anon_super_fc);
1244
1245static int test_keyed_super(struct super_block *sb, struct fs_context *fc)
1246{
1247 return sb->s_fs_info == fc->s_fs_info;
1248}
1249
1250static int test_single_super(struct super_block *s, struct fs_context *fc)
1251{
1252 return 1;
1253}
1254
1255static int vfs_get_super(struct fs_context *fc,
1256 int (*test)(struct super_block *, struct fs_context *),
1257 int (*fill_super)(struct super_block *sb,
1258 struct fs_context *fc))
1259{
1260 struct super_block *sb;
1261 int err;
1262
1263 sb = sget_fc(fc, test, set_anon_super_fc);
1264 if (IS_ERR(sb))
1265 return PTR_ERR(sb);
1266
1267 if (!sb->s_root) {
1268 err = fill_super(sb, fc);
1269 if (err)
1270 goto error;
1271
1272 sb->s_flags |= SB_ACTIVE;
1273 }
1274
1275 fc->root = dget(sb->s_root);
1276 return 0;
1277
1278error:
1279 deactivate_locked_super(sb);
1280 return err;
1281}
1282
1283int get_tree_nodev(struct fs_context *fc,
1284 int (*fill_super)(struct super_block *sb,
1285 struct fs_context *fc))
1286{
1287 return vfs_get_super(fc, NULL, fill_super);
1288}
1289EXPORT_SYMBOL(get_tree_nodev);
1290
1291int get_tree_single(struct fs_context *fc,
1292 int (*fill_super)(struct super_block *sb,
1293 struct fs_context *fc))
1294{
1295 return vfs_get_super(fc, test_single_super, fill_super);
1296}
1297EXPORT_SYMBOL(get_tree_single);
1298
1299int get_tree_keyed(struct fs_context *fc,
1300 int (*fill_super)(struct super_block *sb,
1301 struct fs_context *fc),
1302 void *key)
1303{
1304 fc->s_fs_info = key;
1305 return vfs_get_super(fc, test_keyed_super, fill_super);
1306}
1307EXPORT_SYMBOL(get_tree_keyed);
1308
1309static int set_bdev_super(struct super_block *s, void *data)
1310{
1311 s->s_dev = *(dev_t *)data;
1312 return 0;
1313}
1314
1315static int super_s_dev_set(struct super_block *s, struct fs_context *fc)
1316{
1317 return set_bdev_super(s, fc->sget_key);
1318}
1319
1320static int super_s_dev_test(struct super_block *s, struct fs_context *fc)
1321{
1322 return !(s->s_iflags & SB_I_RETIRED) &&
1323 s->s_dev == *(dev_t *)fc->sget_key;
1324}
1325
1326/**
1327 * sget_dev - Find or create a superblock by device number
1328 * @fc: Filesystem context.
1329 * @dev: device number
1330 *
1331 * Find or create a superblock using the provided device number that
1332 * will be stored in fc->sget_key.
1333 *
1334 * If an extant superblock is matched, then that will be returned with
1335 * an elevated reference count that the caller must transfer or discard.
1336 *
1337 * If no match is made, a new superblock will be allocated and basic
1338 * initialisation will be performed (s_type, s_fs_info, s_id, s_dev will
1339 * be set). The superblock will be published and it will be returned in
1340 * a partially constructed state with SB_BORN and SB_ACTIVE as yet
1341 * unset.
1342 *
1343 * Return: an existing or newly created superblock on success, an error
1344 * pointer on failure.
1345 */
1346struct super_block *sget_dev(struct fs_context *fc, dev_t dev)
1347{
1348 fc->sget_key = &dev;
1349 return sget_fc(fc, super_s_dev_test, super_s_dev_set);
1350}
1351EXPORT_SYMBOL(sget_dev);
1352
1353#ifdef CONFIG_BLOCK
1354/*
1355 * Lock the superblock that is holder of the bdev. Returns the superblock
1356 * pointer if we successfully locked the superblock and it is alive. Otherwise
1357 * we return NULL and just unlock bdev->bd_holder_lock.
1358 *
1359 * The function must be called with bdev->bd_holder_lock and releases it.
1360 */
1361static struct super_block *bdev_super_lock(struct block_device *bdev, bool excl)
1362 __releases(&bdev->bd_holder_lock)
1363{
1364 struct super_block *sb = bdev->bd_holder;
1365 bool locked;
1366
1367 lockdep_assert_held(&bdev->bd_holder_lock);
1368 lockdep_assert_not_held(&sb->s_umount);
1369 lockdep_assert_not_held(&bdev->bd_disk->open_mutex);
1370
1371 /* Make sure sb doesn't go away from under us */
1372 spin_lock(&sb_lock);
1373 sb->s_count++;
1374 spin_unlock(&sb_lock);
1375
1376 mutex_unlock(&bdev->bd_holder_lock);
1377
1378 locked = super_lock(sb, excl);
1379
1380 /*
1381 * If the superblock wasn't already SB_DYING then we hold
1382 * s_umount and can safely drop our temporary reference.
1383 */
1384 put_super(sb);
1385
1386 if (!locked)
1387 return NULL;
1388
1389 if (!sb->s_root || !(sb->s_flags & SB_ACTIVE)) {
1390 super_unlock(sb, excl);
1391 return NULL;
1392 }
1393
1394 return sb;
1395}
1396
1397static void fs_bdev_mark_dead(struct block_device *bdev, bool surprise)
1398{
1399 struct super_block *sb;
1400
1401 sb = bdev_super_lock(bdev, false);
1402 if (!sb)
1403 return;
1404
1405 if (!surprise)
1406 sync_filesystem(sb);
1407 shrink_dcache_sb(sb);
1408 invalidate_inodes(sb);
1409 if (sb->s_op->shutdown)
1410 sb->s_op->shutdown(sb);
1411
1412 super_unlock_shared(sb);
1413}
1414
1415static void fs_bdev_sync(struct block_device *bdev)
1416{
1417 struct super_block *sb;
1418
1419 sb = bdev_super_lock(bdev, false);
1420 if (!sb)
1421 return;
1422
1423 sync_filesystem(sb);
1424 super_unlock_shared(sb);
1425}
1426
1427static struct super_block *get_bdev_super(struct block_device *bdev)
1428{
1429 bool active = false;
1430 struct super_block *sb;
1431
1432 sb = bdev_super_lock(bdev, true);
1433 if (sb) {
1434 active = atomic_inc_not_zero(&sb->s_active);
1435 super_unlock_excl(sb);
1436 }
1437 if (!active)
1438 return NULL;
1439 return sb;
1440}
1441
1442/**
1443 * fs_bdev_freeze - freeze owning filesystem of block device
1444 * @bdev: block device
1445 *
1446 * Freeze the filesystem that owns this block device if it is still
1447 * active.
1448 *
1449 * A filesystem that owns multiple block devices may be frozen from each
1450 * block device and won't be unfrozen until all block devices are
1451 * unfrozen. Each block device can only freeze the filesystem once as we
1452 * nest freezes for block devices in the block layer.
1453 *
1454 * Return: If the freeze was successful zero is returned. If the freeze
1455 * failed a negative error code is returned.
1456 */
1457static int fs_bdev_freeze(struct block_device *bdev)
1458{
1459 struct super_block *sb;
1460 int error = 0;
1461
1462 lockdep_assert_held(&bdev->bd_fsfreeze_mutex);
1463
1464 sb = get_bdev_super(bdev);
1465 if (!sb)
1466 return -EINVAL;
1467
1468 if (sb->s_op->freeze_super)
1469 error = sb->s_op->freeze_super(sb,
1470 FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE);
1471 else
1472 error = freeze_super(sb,
1473 FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE);
1474 if (!error)
1475 error = sync_blockdev(bdev);
1476 deactivate_super(sb);
1477 return error;
1478}
1479
1480/**
1481 * fs_bdev_thaw - thaw owning filesystem of block device
1482 * @bdev: block device
1483 *
1484 * Thaw the filesystem that owns this block device.
1485 *
1486 * A filesystem that owns multiple block devices may be frozen from each
1487 * block device and won't be unfrozen until all block devices are
1488 * unfrozen. Each block device can only freeze the filesystem once as we
1489 * nest freezes for block devices in the block layer.
1490 *
1491 * Return: If the thaw was successful zero is returned. If the thaw
1492 * failed a negative error code is returned. If this function
1493 * returns zero it doesn't mean that the filesystem is unfrozen
1494 * as it may have been frozen multiple times (kernel may hold a
1495 * freeze or might be frozen from other block devices).
1496 */
1497static int fs_bdev_thaw(struct block_device *bdev)
1498{
1499 struct super_block *sb;
1500 int error;
1501
1502 lockdep_assert_held(&bdev->bd_fsfreeze_mutex);
1503
1504 sb = get_bdev_super(bdev);
1505 if (WARN_ON_ONCE(!sb))
1506 return -EINVAL;
1507
1508 if (sb->s_op->thaw_super)
1509 error = sb->s_op->thaw_super(sb,
1510 FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE);
1511 else
1512 error = thaw_super(sb,
1513 FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE);
1514 deactivate_super(sb);
1515 return error;
1516}
1517
1518const struct blk_holder_ops fs_holder_ops = {
1519 .mark_dead = fs_bdev_mark_dead,
1520 .sync = fs_bdev_sync,
1521 .freeze = fs_bdev_freeze,
1522 .thaw = fs_bdev_thaw,
1523};
1524EXPORT_SYMBOL_GPL(fs_holder_ops);
1525
1526int setup_bdev_super(struct super_block *sb, int sb_flags,
1527 struct fs_context *fc)
1528{
1529 blk_mode_t mode = sb_open_mode(sb_flags);
1530 struct file *bdev_file;
1531 struct block_device *bdev;
1532
1533 bdev_file = bdev_file_open_by_dev(sb->s_dev, mode, sb, &fs_holder_ops);
1534 if (IS_ERR(bdev_file)) {
1535 if (fc)
1536 errorf(fc, "%s: Can't open blockdev", fc->source);
1537 return PTR_ERR(bdev_file);
1538 }
1539 bdev = file_bdev(bdev_file);
1540
1541 /*
1542 * This really should be in blkdev_get_by_dev, but right now can't due
1543 * to legacy issues that require us to allow opening a block device node
1544 * writable from userspace even for a read-only block device.
1545 */
1546 if ((mode & BLK_OPEN_WRITE) && bdev_read_only(bdev)) {
1547 bdev_fput(bdev_file);
1548 return -EACCES;
1549 }
1550
1551 /*
1552 * It is enough to check bdev was not frozen before we set
1553 * s_bdev as freezing will wait until SB_BORN is set.
1554 */
1555 if (atomic_read(&bdev->bd_fsfreeze_count) > 0) {
1556 if (fc)
1557 warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
1558 bdev_fput(bdev_file);
1559 return -EBUSY;
1560 }
1561 spin_lock(&sb_lock);
1562 sb->s_bdev_file = bdev_file;
1563 sb->s_bdev = bdev;
1564 sb->s_bdi = bdi_get(bdev->bd_disk->bdi);
1565 if (bdev_stable_writes(bdev))
1566 sb->s_iflags |= SB_I_STABLE_WRITES;
1567 spin_unlock(&sb_lock);
1568
1569 snprintf(sb->s_id, sizeof(sb->s_id), "%pg", bdev);
1570 shrinker_debugfs_rename(sb->s_shrink, "sb-%s:%s", sb->s_type->name,
1571 sb->s_id);
1572 sb_set_blocksize(sb, block_size(bdev));
1573 return 0;
1574}
1575EXPORT_SYMBOL_GPL(setup_bdev_super);
1576
1577/**
1578 * get_tree_bdev - Get a superblock based on a single block device
1579 * @fc: The filesystem context holding the parameters
1580 * @fill_super: Helper to initialise a new superblock
1581 */
1582int get_tree_bdev(struct fs_context *fc,
1583 int (*fill_super)(struct super_block *,
1584 struct fs_context *))
1585{
1586 struct super_block *s;
1587 int error = 0;
1588 dev_t dev;
1589
1590 if (!fc->source)
1591 return invalf(fc, "No source specified");
1592
1593 error = lookup_bdev(fc->source, &dev);
1594 if (error) {
1595 errorf(fc, "%s: Can't lookup blockdev", fc->source);
1596 return error;
1597 }
1598
1599 fc->sb_flags |= SB_NOSEC;
1600 s = sget_dev(fc, dev);
1601 if (IS_ERR(s))
1602 return PTR_ERR(s);
1603
1604 if (s->s_root) {
1605 /* Don't summarily change the RO/RW state. */
1606 if ((fc->sb_flags ^ s->s_flags) & SB_RDONLY) {
1607 warnf(fc, "%pg: Can't mount, would change RO state", s->s_bdev);
1608 deactivate_locked_super(s);
1609 return -EBUSY;
1610 }
1611 } else {
1612 error = setup_bdev_super(s, fc->sb_flags, fc);
1613 if (!error)
1614 error = fill_super(s, fc);
1615 if (error) {
1616 deactivate_locked_super(s);
1617 return error;
1618 }
1619 s->s_flags |= SB_ACTIVE;
1620 }
1621
1622 BUG_ON(fc->root);
1623 fc->root = dget(s->s_root);
1624 return 0;
1625}
1626EXPORT_SYMBOL(get_tree_bdev);
1627
1628static int test_bdev_super(struct super_block *s, void *data)
1629{
1630 return !(s->s_iflags & SB_I_RETIRED) && s->s_dev == *(dev_t *)data;
1631}
1632
1633struct dentry *mount_bdev(struct file_system_type *fs_type,
1634 int flags, const char *dev_name, void *data,
1635 int (*fill_super)(struct super_block *, void *, int))
1636{
1637 struct super_block *s;
1638 int error;
1639 dev_t dev;
1640
1641 error = lookup_bdev(dev_name, &dev);
1642 if (error)
1643 return ERR_PTR(error);
1644
1645 flags |= SB_NOSEC;
1646 s = sget(fs_type, test_bdev_super, set_bdev_super, flags, &dev);
1647 if (IS_ERR(s))
1648 return ERR_CAST(s);
1649
1650 if (s->s_root) {
1651 if ((flags ^ s->s_flags) & SB_RDONLY) {
1652 deactivate_locked_super(s);
1653 return ERR_PTR(-EBUSY);
1654 }
1655 } else {
1656 error = setup_bdev_super(s, flags, NULL);
1657 if (!error)
1658 error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1659 if (error) {
1660 deactivate_locked_super(s);
1661 return ERR_PTR(error);
1662 }
1663
1664 s->s_flags |= SB_ACTIVE;
1665 }
1666
1667 return dget(s->s_root);
1668}
1669EXPORT_SYMBOL(mount_bdev);
1670
1671void kill_block_super(struct super_block *sb)
1672{
1673 struct block_device *bdev = sb->s_bdev;
1674
1675 generic_shutdown_super(sb);
1676 if (bdev) {
1677 sync_blockdev(bdev);
1678 bdev_fput(sb->s_bdev_file);
1679 }
1680}
1681
1682EXPORT_SYMBOL(kill_block_super);
1683#endif
1684
1685struct dentry *mount_nodev(struct file_system_type *fs_type,
1686 int flags, void *data,
1687 int (*fill_super)(struct super_block *, void *, int))
1688{
1689 int error;
1690 struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1691
1692 if (IS_ERR(s))
1693 return ERR_CAST(s);
1694
1695 error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1696 if (error) {
1697 deactivate_locked_super(s);
1698 return ERR_PTR(error);
1699 }
1700 s->s_flags |= SB_ACTIVE;
1701 return dget(s->s_root);
1702}
1703EXPORT_SYMBOL(mount_nodev);
1704
1705int reconfigure_single(struct super_block *s,
1706 int flags, void *data)
1707{
1708 struct fs_context *fc;
1709 int ret;
1710
1711 /* The caller really need to be passing fc down into mount_single(),
1712 * then a chunk of this can be removed. [Bollocks -- AV]
1713 * Better yet, reconfiguration shouldn't happen, but rather the second
1714 * mount should be rejected if the parameters are not compatible.
1715 */
1716 fc = fs_context_for_reconfigure(s->s_root, flags, MS_RMT_MASK);
1717 if (IS_ERR(fc))
1718 return PTR_ERR(fc);
1719
1720 ret = parse_monolithic_mount_data(fc, data);
1721 if (ret < 0)
1722 goto out;
1723
1724 ret = reconfigure_super(fc);
1725out:
1726 put_fs_context(fc);
1727 return ret;
1728}
1729
1730static int compare_single(struct super_block *s, void *p)
1731{
1732 return 1;
1733}
1734
1735struct dentry *mount_single(struct file_system_type *fs_type,
1736 int flags, void *data,
1737 int (*fill_super)(struct super_block *, void *, int))
1738{
1739 struct super_block *s;
1740 int error;
1741
1742 s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1743 if (IS_ERR(s))
1744 return ERR_CAST(s);
1745 if (!s->s_root) {
1746 error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1747 if (!error)
1748 s->s_flags |= SB_ACTIVE;
1749 } else {
1750 error = reconfigure_single(s, flags, data);
1751 }
1752 if (unlikely(error)) {
1753 deactivate_locked_super(s);
1754 return ERR_PTR(error);
1755 }
1756 return dget(s->s_root);
1757}
1758EXPORT_SYMBOL(mount_single);
1759
1760/**
1761 * vfs_get_tree - Get the mountable root
1762 * @fc: The superblock configuration context.
1763 *
1764 * The filesystem is invoked to get or create a superblock which can then later
1765 * be used for mounting. The filesystem places a pointer to the root to be
1766 * used for mounting in @fc->root.
1767 */
1768int vfs_get_tree(struct fs_context *fc)
1769{
1770 struct super_block *sb;
1771 int error;
1772
1773 if (fc->root)
1774 return -EBUSY;
1775
1776 /* Get the mountable root in fc->root, with a ref on the root and a ref
1777 * on the superblock.
1778 */
1779 error = fc->ops->get_tree(fc);
1780 if (error < 0)
1781 return error;
1782
1783 if (!fc->root) {
1784 pr_err("Filesystem %s get_tree() didn't set fc->root\n",
1785 fc->fs_type->name);
1786 /* We don't know what the locking state of the superblock is -
1787 * if there is a superblock.
1788 */
1789 BUG();
1790 }
1791
1792 sb = fc->root->d_sb;
1793 WARN_ON(!sb->s_bdi);
1794
1795 /*
1796 * super_wake() contains a memory barrier which also care of
1797 * ordering for super_cache_count(). We place it before setting
1798 * SB_BORN as the data dependency between the two functions is
1799 * the superblock structure contents that we just set up, not
1800 * the SB_BORN flag.
1801 */
1802 super_wake(sb, SB_BORN);
1803
1804 error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
1805 if (unlikely(error)) {
1806 fc_drop_locked(fc);
1807 return error;
1808 }
1809
1810 /*
1811 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1812 * but s_maxbytes was an unsigned long long for many releases. Throw
1813 * this warning for a little while to try and catch filesystems that
1814 * violate this rule.
1815 */
1816 WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1817 "negative value (%lld)\n", fc->fs_type->name, sb->s_maxbytes);
1818
1819 return 0;
1820}
1821EXPORT_SYMBOL(vfs_get_tree);
1822
1823/*
1824 * Setup private BDI for given superblock. It gets automatically cleaned up
1825 * in generic_shutdown_super().
1826 */
1827int super_setup_bdi_name(struct super_block *sb, char *fmt, ...)
1828{
1829 struct backing_dev_info *bdi;
1830 int err;
1831 va_list args;
1832
1833 bdi = bdi_alloc(NUMA_NO_NODE);
1834 if (!bdi)
1835 return -ENOMEM;
1836
1837 va_start(args, fmt);
1838 err = bdi_register_va(bdi, fmt, args);
1839 va_end(args);
1840 if (err) {
1841 bdi_put(bdi);
1842 return err;
1843 }
1844 WARN_ON(sb->s_bdi != &noop_backing_dev_info);
1845 sb->s_bdi = bdi;
1846 sb->s_iflags |= SB_I_PERSB_BDI;
1847
1848 return 0;
1849}
1850EXPORT_SYMBOL(super_setup_bdi_name);
1851
1852/*
1853 * Setup private BDI for given superblock. I gets automatically cleaned up
1854 * in generic_shutdown_super().
1855 */
1856int super_setup_bdi(struct super_block *sb)
1857{
1858 static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
1859
1860 return super_setup_bdi_name(sb, "%.28s-%ld", sb->s_type->name,
1861 atomic_long_inc_return(&bdi_seq));
1862}
1863EXPORT_SYMBOL(super_setup_bdi);
1864
1865/**
1866 * sb_wait_write - wait until all writers to given file system finish
1867 * @sb: the super for which we wait
1868 * @level: type of writers we wait for (normal vs page fault)
1869 *
1870 * This function waits until there are no writers of given type to given file
1871 * system.
1872 */
1873static void sb_wait_write(struct super_block *sb, int level)
1874{
1875 percpu_down_write(sb->s_writers.rw_sem + level-1);
1876}
1877
1878/*
1879 * We are going to return to userspace and forget about these locks, the
1880 * ownership goes to the caller of thaw_super() which does unlock().
1881 */
1882static void lockdep_sb_freeze_release(struct super_block *sb)
1883{
1884 int level;
1885
1886 for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1887 percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1888}
1889
1890/*
1891 * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
1892 */
1893static void lockdep_sb_freeze_acquire(struct super_block *sb)
1894{
1895 int level;
1896
1897 for (level = 0; level < SB_FREEZE_LEVELS; ++level)
1898 percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1899}
1900
1901static void sb_freeze_unlock(struct super_block *sb, int level)
1902{
1903 for (level--; level >= 0; level--)
1904 percpu_up_write(sb->s_writers.rw_sem + level);
1905}
1906
1907static int wait_for_partially_frozen(struct super_block *sb)
1908{
1909 int ret = 0;
1910
1911 do {
1912 unsigned short old = sb->s_writers.frozen;
1913
1914 up_write(&sb->s_umount);
1915 ret = wait_var_event_killable(&sb->s_writers.frozen,
1916 sb->s_writers.frozen != old);
1917 down_write(&sb->s_umount);
1918 } while (ret == 0 &&
1919 sb->s_writers.frozen != SB_UNFROZEN &&
1920 sb->s_writers.frozen != SB_FREEZE_COMPLETE);
1921
1922 return ret;
1923}
1924
1925#define FREEZE_HOLDERS (FREEZE_HOLDER_KERNEL | FREEZE_HOLDER_USERSPACE)
1926#define FREEZE_FLAGS (FREEZE_HOLDERS | FREEZE_MAY_NEST)
1927
1928static inline int freeze_inc(struct super_block *sb, enum freeze_holder who)
1929{
1930 WARN_ON_ONCE((who & ~FREEZE_FLAGS));
1931 WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
1932
1933 if (who & FREEZE_HOLDER_KERNEL)
1934 ++sb->s_writers.freeze_kcount;
1935 if (who & FREEZE_HOLDER_USERSPACE)
1936 ++sb->s_writers.freeze_ucount;
1937 return sb->s_writers.freeze_kcount + sb->s_writers.freeze_ucount;
1938}
1939
1940static inline int freeze_dec(struct super_block *sb, enum freeze_holder who)
1941{
1942 WARN_ON_ONCE((who & ~FREEZE_FLAGS));
1943 WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
1944
1945 if ((who & FREEZE_HOLDER_KERNEL) && sb->s_writers.freeze_kcount)
1946 --sb->s_writers.freeze_kcount;
1947 if ((who & FREEZE_HOLDER_USERSPACE) && sb->s_writers.freeze_ucount)
1948 --sb->s_writers.freeze_ucount;
1949 return sb->s_writers.freeze_kcount + sb->s_writers.freeze_ucount;
1950}
1951
1952static inline bool may_freeze(struct super_block *sb, enum freeze_holder who)
1953{
1954 WARN_ON_ONCE((who & ~FREEZE_FLAGS));
1955 WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
1956
1957 if (who & FREEZE_HOLDER_KERNEL)
1958 return (who & FREEZE_MAY_NEST) ||
1959 sb->s_writers.freeze_kcount == 0;
1960 if (who & FREEZE_HOLDER_USERSPACE)
1961 return (who & FREEZE_MAY_NEST) ||
1962 sb->s_writers.freeze_ucount == 0;
1963 return false;
1964}
1965
1966/**
1967 * freeze_super - lock the filesystem and force it into a consistent state
1968 * @sb: the super to lock
1969 * @who: context that wants to freeze
1970 *
1971 * Syncs the super to make sure the filesystem is consistent and calls the fs's
1972 * freeze_fs. Subsequent calls to this without first thawing the fs may return
1973 * -EBUSY.
1974 *
1975 * @who should be:
1976 * * %FREEZE_HOLDER_USERSPACE if userspace wants to freeze the fs;
1977 * * %FREEZE_HOLDER_KERNEL if the kernel wants to freeze the fs.
1978 * * %FREEZE_MAY_NEST whether nesting freeze and thaw requests is allowed.
1979 *
1980 * The @who argument distinguishes between the kernel and userspace trying to
1981 * freeze the filesystem. Although there cannot be multiple kernel freezes or
1982 * multiple userspace freezes in effect at any given time, the kernel and
1983 * userspace can both hold a filesystem frozen. The filesystem remains frozen
1984 * until there are no kernel or userspace freezes in effect.
1985 *
1986 * A filesystem may hold multiple devices and thus a filesystems may be
1987 * frozen through the block layer via multiple block devices. In this
1988 * case the request is marked as being allowed to nest by passing
1989 * FREEZE_MAY_NEST. The filesystem remains frozen until all block
1990 * devices are unfrozen. If multiple freezes are attempted without
1991 * FREEZE_MAY_NEST -EBUSY will be returned.
1992 *
1993 * During this function, sb->s_writers.frozen goes through these values:
1994 *
1995 * SB_UNFROZEN: File system is normal, all writes progress as usual.
1996 *
1997 * SB_FREEZE_WRITE: The file system is in the process of being frozen. New
1998 * writes should be blocked, though page faults are still allowed. We wait for
1999 * all writes to complete and then proceed to the next stage.
2000 *
2001 * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
2002 * but internal fs threads can still modify the filesystem (although they
2003 * should not dirty new pages or inodes), writeback can run etc. After waiting
2004 * for all running page faults we sync the filesystem which will clean all
2005 * dirty pages and inodes (no new dirty pages or inodes can be created when
2006 * sync is running).
2007 *
2008 * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
2009 * modification are blocked (e.g. XFS preallocation truncation on inode
2010 * reclaim). This is usually implemented by blocking new transactions for
2011 * filesystems that have them and need this additional guard. After all
2012 * internal writers are finished we call ->freeze_fs() to finish filesystem
2013 * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
2014 * mostly auxiliary for filesystems to verify they do not modify frozen fs.
2015 *
2016 * sb->s_writers.frozen is protected by sb->s_umount.
2017 *
2018 * Return: If the freeze was successful zero is returned. If the freeze
2019 * failed a negative error code is returned.
2020 */
2021int freeze_super(struct super_block *sb, enum freeze_holder who)
2022{
2023 int ret;
2024
2025 if (!super_lock_excl(sb)) {
2026 WARN_ON_ONCE("Dying superblock while freezing!");
2027 return -EINVAL;
2028 }
2029 atomic_inc(&sb->s_active);
2030
2031retry:
2032 if (sb->s_writers.frozen == SB_FREEZE_COMPLETE) {
2033 if (may_freeze(sb, who))
2034 ret = !!WARN_ON_ONCE(freeze_inc(sb, who) == 1);
2035 else
2036 ret = -EBUSY;
2037 /* All freezers share a single active reference. */
2038 deactivate_locked_super(sb);
2039 return ret;
2040 }
2041
2042 if (sb->s_writers.frozen != SB_UNFROZEN) {
2043 ret = wait_for_partially_frozen(sb);
2044 if (ret) {
2045 deactivate_locked_super(sb);
2046 return ret;
2047 }
2048
2049 goto retry;
2050 }
2051
2052 if (sb_rdonly(sb)) {
2053 /* Nothing to do really... */
2054 WARN_ON_ONCE(freeze_inc(sb, who) > 1);
2055 sb->s_writers.frozen = SB_FREEZE_COMPLETE;
2056 wake_up_var(&sb->s_writers.frozen);
2057 super_unlock_excl(sb);
2058 return 0;
2059 }
2060
2061 sb->s_writers.frozen = SB_FREEZE_WRITE;
2062 /* Release s_umount to preserve sb_start_write -> s_umount ordering */
2063 super_unlock_excl(sb);
2064 sb_wait_write(sb, SB_FREEZE_WRITE);
2065 __super_lock_excl(sb);
2066
2067 /* Now we go and block page faults... */
2068 sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
2069 sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
2070
2071 /* All writers are done so after syncing there won't be dirty data */
2072 ret = sync_filesystem(sb);
2073 if (ret) {
2074 sb->s_writers.frozen = SB_UNFROZEN;
2075 sb_freeze_unlock(sb, SB_FREEZE_PAGEFAULT);
2076 wake_up_var(&sb->s_writers.frozen);
2077 deactivate_locked_super(sb);
2078 return ret;
2079 }
2080
2081 /* Now wait for internal filesystem counter */
2082 sb->s_writers.frozen = SB_FREEZE_FS;
2083 sb_wait_write(sb, SB_FREEZE_FS);
2084
2085 if (sb->s_op->freeze_fs) {
2086 ret = sb->s_op->freeze_fs(sb);
2087 if (ret) {
2088 printk(KERN_ERR
2089 "VFS:Filesystem freeze failed\n");
2090 sb->s_writers.frozen = SB_UNFROZEN;
2091 sb_freeze_unlock(sb, SB_FREEZE_FS);
2092 wake_up_var(&sb->s_writers.frozen);
2093 deactivate_locked_super(sb);
2094 return ret;
2095 }
2096 }
2097 /*
2098 * For debugging purposes so that fs can warn if it sees write activity
2099 * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
2100 */
2101 WARN_ON_ONCE(freeze_inc(sb, who) > 1);
2102 sb->s_writers.frozen = SB_FREEZE_COMPLETE;
2103 wake_up_var(&sb->s_writers.frozen);
2104 lockdep_sb_freeze_release(sb);
2105 super_unlock_excl(sb);
2106 return 0;
2107}
2108EXPORT_SYMBOL(freeze_super);
2109
2110/*
2111 * Undoes the effect of a freeze_super_locked call. If the filesystem is
2112 * frozen both by userspace and the kernel, a thaw call from either source
2113 * removes that state without releasing the other state or unlocking the
2114 * filesystem.
2115 */
2116static int thaw_super_locked(struct super_block *sb, enum freeze_holder who)
2117{
2118 int error = -EINVAL;
2119
2120 if (sb->s_writers.frozen != SB_FREEZE_COMPLETE)
2121 goto out_unlock;
2122
2123 /*
2124 * All freezers share a single active reference.
2125 * So just unlock in case there are any left.
2126 */
2127 if (freeze_dec(sb, who))
2128 goto out_unlock;
2129
2130 if (sb_rdonly(sb)) {
2131 sb->s_writers.frozen = SB_UNFROZEN;
2132 wake_up_var(&sb->s_writers.frozen);
2133 goto out_deactivate;
2134 }
2135
2136 lockdep_sb_freeze_acquire(sb);
2137
2138 if (sb->s_op->unfreeze_fs) {
2139 error = sb->s_op->unfreeze_fs(sb);
2140 if (error) {
2141 pr_err("VFS: Filesystem thaw failed\n");
2142 freeze_inc(sb, who);
2143 lockdep_sb_freeze_release(sb);
2144 goto out_unlock;
2145 }
2146 }
2147
2148 sb->s_writers.frozen = SB_UNFROZEN;
2149 wake_up_var(&sb->s_writers.frozen);
2150 sb_freeze_unlock(sb, SB_FREEZE_FS);
2151out_deactivate:
2152 deactivate_locked_super(sb);
2153 return 0;
2154
2155out_unlock:
2156 super_unlock_excl(sb);
2157 return error;
2158}
2159
2160/**
2161 * thaw_super -- unlock filesystem
2162 * @sb: the super to thaw
2163 * @who: context that wants to freeze
2164 *
2165 * Unlocks the filesystem and marks it writeable again after freeze_super()
2166 * if there are no remaining freezes on the filesystem.
2167 *
2168 * @who should be:
2169 * * %FREEZE_HOLDER_USERSPACE if userspace wants to thaw the fs;
2170 * * %FREEZE_HOLDER_KERNEL if the kernel wants to thaw the fs.
2171 * * %FREEZE_MAY_NEST whether nesting freeze and thaw requests is allowed
2172 *
2173 * A filesystem may hold multiple devices and thus a filesystems may
2174 * have been frozen through the block layer via multiple block devices.
2175 * The filesystem remains frozen until all block devices are unfrozen.
2176 */
2177int thaw_super(struct super_block *sb, enum freeze_holder who)
2178{
2179 if (!super_lock_excl(sb)) {
2180 WARN_ON_ONCE("Dying superblock while thawing!");
2181 return -EINVAL;
2182 }
2183 return thaw_super_locked(sb, who);
2184}
2185EXPORT_SYMBOL(thaw_super);
2186
2187/*
2188 * Create workqueue for deferred direct IO completions. We allocate the
2189 * workqueue when it's first needed. This avoids creating workqueue for
2190 * filesystems that don't need it and also allows us to create the workqueue
2191 * late enough so the we can include s_id in the name of the workqueue.
2192 */
2193int sb_init_dio_done_wq(struct super_block *sb)
2194{
2195 struct workqueue_struct *old;
2196 struct workqueue_struct *wq = alloc_workqueue("dio/%s",
2197 WQ_MEM_RECLAIM, 0,
2198 sb->s_id);
2199 if (!wq)
2200 return -ENOMEM;
2201 /*
2202 * This has to be atomic as more DIOs can race to create the workqueue
2203 */
2204 old = cmpxchg(&sb->s_dio_done_wq, NULL, wq);
2205 /* Someone created workqueue before us? Free ours... */
2206 if (old)
2207 destroy_workqueue(wq);
2208 return 0;
2209}
2210EXPORT_SYMBOL_GPL(sb_init_dio_done_wq);