source: src/linux/universal/linux-4.9/fs/super.c @ 31662

Last change on this file since 31662 was 31662, checked in by brainslayer, 11 days ago

use new squashfs in all kernels

File size: 37.0 KB
Line 
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 <linux/user_namespace.h>
37#include "internal.h"
38
39
40static LIST_HEAD(super_blocks);
41static DEFINE_SPINLOCK(sb_lock);
42
43static char *sb_writers_name[SB_FREEZE_LEVELS] = {
44        "sb_writers",
45        "sb_pagefaults",
46        "sb_internal",
47};
48
49/*
50 * One thing we have to be careful of with a per-sb shrinker is that we don't
51 * drop the last active reference to the superblock from within the shrinker.
52 * If that happens we could trigger unregistering the shrinker from within the
53 * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
54 * take a passive reference to the superblock to avoid this from occurring.
55 */
56static unsigned long super_cache_scan(struct shrinker *shrink,
57                                      struct shrink_control *sc)
58{
59        struct super_block *sb;
60        long    fs_objects = 0;
61        long    total_objects;
62        long    freed = 0;
63        long    dentries;
64        long    inodes;
65
66        sb = container_of(shrink, struct super_block, s_shrink);
67
68        /*
69         * Deadlock avoidance.  We may hold various FS locks, and we don't want
70         * to recurse into the FS that called us in clear_inode() and friends..
71         */
72        if (!(sc->gfp_mask & __GFP_FS))
73                return SHRINK_STOP;
74
75        if (!trylock_super(sb))
76                return SHRINK_STOP;
77
78        if (sb->s_op->nr_cached_objects)
79                fs_objects = sb->s_op->nr_cached_objects(sb, sc);
80
81        inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
82        dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc);
83        total_objects = dentries + inodes + fs_objects + 1;
84        if (!total_objects)
85                total_objects = 1;
86
87        /* proportion the scan between the caches */
88        dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);
89        inodes = mult_frac(sc->nr_to_scan, inodes, total_objects);
90        fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
91
92        /*
93         * prune the dcache first as the icache is pinned by it, then
94         * prune the icache, followed by the filesystem specific caches
95         *
96         * Ensure that we always scan at least one object - memcg kmem
97         * accounting uses this to fully empty the caches.
98         */
99        sc->nr_to_scan = dentries + 1;
100        freed = prune_dcache_sb(sb, sc);
101        sc->nr_to_scan = inodes + 1;
102        freed += prune_icache_sb(sb, sc);
103
104        if (fs_objects) {
105                sc->nr_to_scan = fs_objects + 1;
106                freed += sb->s_op->free_cached_objects(sb, sc);
107        }
108
109        up_read(&sb->s_umount);
110        return freed;
111}
112
113static unsigned long super_cache_count(struct shrinker *shrink,
114                                       struct shrink_control *sc)
115{
116        struct super_block *sb;
117        long    total_objects = 0;
118
119        sb = container_of(shrink, struct super_block, s_shrink);
120
121        /*
122         * Don't call trylock_super as it is a potential
123         * scalability bottleneck. The counts could get updated
124         * between super_cache_count and super_cache_scan anyway.
125         * Call to super_cache_count with shrinker_rwsem held
126         * ensures the safety of call to list_lru_shrink_count() and
127         * s_op->nr_cached_objects().
128         */
129        if (sb->s_op && sb->s_op->nr_cached_objects)
130                total_objects = sb->s_op->nr_cached_objects(sb, sc);
131
132        total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
133        total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
134
135        total_objects = vfs_pressure_ratio(total_objects);
136        return total_objects;
137}
138
139static void destroy_super_work(struct work_struct *work)
140{
141        struct super_block *s = container_of(work, struct super_block,
142                                                        destroy_work);
143        int i;
144
145        for (i = 0; i < SB_FREEZE_LEVELS; i++)
146                percpu_free_rwsem(&s->s_writers.rw_sem[i]);
147        kfree(s);
148}
149
150static void destroy_super_rcu(struct rcu_head *head)
151{
152        struct super_block *s = container_of(head, struct super_block, rcu);
153        INIT_WORK(&s->destroy_work, destroy_super_work);
154        schedule_work(&s->destroy_work);
155}
156
157/**
158 *      destroy_super   -       frees a superblock
159 *      @s: superblock to free
160 *
161 *      Frees a superblock.
162 */
163static void destroy_super(struct super_block *s)
164{
165        list_lru_destroy(&s->s_dentry_lru);
166        list_lru_destroy(&s->s_inode_lru);
167        security_sb_free(s);
168        WARN_ON(!list_empty(&s->s_mounts));
169        put_user_ns(s->s_user_ns);
170        kfree(s->s_subtype);
171        kfree(s->s_options);
172        call_rcu(&s->rcu, destroy_super_rcu);
173}
174
175/**
176 *      alloc_super     -       create new superblock
177 *      @type:  filesystem type superblock should belong to
178 *      @flags: the mount flags
179 *      @user_ns: User namespace for the super_block
180 *
181 *      Allocates and initializes a new &struct super_block.  alloc_super()
182 *      returns a pointer new superblock or %NULL if allocation had failed.
183 */
184static struct super_block *alloc_super(struct file_system_type *type, int flags,
185                                       struct user_namespace *user_ns)
186{
187        struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
188        static const struct super_operations default_op;
189        int i;
190
191        if (!s)
192                return NULL;
193
194        INIT_LIST_HEAD(&s->s_mounts);
195        s->s_user_ns = get_user_ns(user_ns);
196
197        if (security_sb_alloc(s))
198                goto fail;
199
200        for (i = 0; i < SB_FREEZE_LEVELS; i++) {
201                if (__percpu_init_rwsem(&s->s_writers.rw_sem[i],
202                                        sb_writers_name[i],
203                                        &type->s_writers_key[i]))
204                        goto fail;
205        }
206        init_waitqueue_head(&s->s_writers.wait_unfrozen);
207        s->s_bdi = &noop_backing_dev_info;
208        s->s_flags = flags;
209        if (s->s_user_ns != &init_user_ns)
210                s->s_iflags |= SB_I_NODEV;
211        INIT_HLIST_NODE(&s->s_instances);
212        INIT_HLIST_BL_HEAD(&s->s_anon);
213        mutex_init(&s->s_sync_lock);
214        INIT_LIST_HEAD(&s->s_inodes);
215        spin_lock_init(&s->s_inode_list_lock);
216        INIT_LIST_HEAD(&s->s_inodes_wb);
217        spin_lock_init(&s->s_inode_wblist_lock);
218
219        if (list_lru_init_memcg(&s->s_dentry_lru))
220                goto fail;
221        if (list_lru_init_memcg(&s->s_inode_lru))
222                goto fail;
223
224        init_rwsem(&s->s_umount);
225        lockdep_set_class(&s->s_umount, &type->s_umount_key);
226        /*
227         * sget() can have s_umount recursion.
228         *
229         * When it cannot find a suitable sb, it allocates a new
230         * one (this one), and tries again to find a suitable old
231         * one.
232         *
233         * In case that succeeds, it will acquire the s_umount
234         * lock of the old one. Since these are clearly distrinct
235         * locks, and this object isn't exposed yet, there's no
236         * risk of deadlocks.
237         *
238         * Annotate this by putting this lock in a different
239         * subclass.
240         */
241        down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
242        s->s_count = 1;
243        atomic_set(&s->s_active, 1);
244        mutex_init(&s->s_vfs_rename_mutex);
245        lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
246        mutex_init(&s->s_dquot.dqio_mutex);
247        mutex_init(&s->s_dquot.dqonoff_mutex);
248        s->s_maxbytes = MAX_NON_LFS;
249        s->s_op = &default_op;
250        s->s_time_gran = 1000000000;
251        s->cleancache_poolid = CLEANCACHE_NO_POOL;
252
253        s->s_shrink.seeks = DEFAULT_SEEKS;
254        s->s_shrink.scan_objects = super_cache_scan;
255        s->s_shrink.count_objects = super_cache_count;
256        s->s_shrink.batch = 1024;
257        s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
258        return s;
259
260fail:
261        destroy_super(s);
262        return NULL;
263}
264
265/* Superblock refcounting  */
266
267/*
268 * Drop a superblock's refcount.  The caller must hold sb_lock.
269 */
270static void __put_super(struct super_block *sb)
271{
272        if (!--sb->s_count) {
273                list_del_init(&sb->s_list);
274                destroy_super(sb);
275        }
276}
277
278/**
279 *      put_super       -       drop a temporary reference to superblock
280 *      @sb: superblock in question
281 *
282 *      Drops a temporary reference, frees superblock if there's no
283 *      references left.
284 */
285static void put_super(struct super_block *sb)
286{
287        spin_lock(&sb_lock);
288        __put_super(sb);
289        spin_unlock(&sb_lock);
290}
291
292
293/**
294 *      deactivate_locked_super -       drop an active reference to superblock
295 *      @s: superblock to deactivate
296 *
297 *      Drops an active reference to superblock, converting it into a temporary
298 *      one if there is no other active references left.  In that case we
299 *      tell fs driver to shut it down and drop the temporary reference we
300 *      had just acquired.
301 *
302 *      Caller holds exclusive lock on superblock; that lock is released.
303 */
304void deactivate_locked_super(struct super_block *s)
305{
306        struct file_system_type *fs = s->s_type;
307        if (atomic_dec_and_test(&s->s_active)) {
308                cleancache_invalidate_fs(s);
309                unregister_shrinker(&s->s_shrink);
310                fs->kill_sb(s);
311
312                /*
313                 * Since list_lru_destroy() may sleep, we cannot call it from
314                 * put_super(), where we hold the sb_lock. Therefore we destroy
315                 * the lru lists right now.
316                 */
317                list_lru_destroy(&s->s_dentry_lru);
318                list_lru_destroy(&s->s_inode_lru);
319
320                put_filesystem(fs);
321                put_super(s);
322        } else {
323                up_write(&s->s_umount);
324        }
325}
326
327EXPORT_SYMBOL(deactivate_locked_super);
328
329/**
330 *      deactivate_super        -       drop an active reference to superblock
331 *      @s: superblock to deactivate
332 *
333 *      Variant of deactivate_locked_super(), except that superblock is *not*
334 *      locked by caller.  If we are going to drop the final active reference,
335 *      lock will be acquired prior to that.
336 */
337void deactivate_super(struct super_block *s)
338{
339        if (!atomic_add_unless(&s->s_active, -1, 1)) {
340                down_write(&s->s_umount);
341                deactivate_locked_super(s);
342        }
343}
344
345EXPORT_SYMBOL(deactivate_super);
346
347/**
348 *      grab_super - acquire an active reference
349 *      @s: reference we are trying to make active
350 *
351 *      Tries to acquire an active reference.  grab_super() is used when we
352 *      had just found a superblock in super_blocks or fs_type->fs_supers
353 *      and want to turn it into a full-blown active reference.  grab_super()
354 *      is called with sb_lock held and drops it.  Returns 1 in case of
355 *      success, 0 if we had failed (superblock contents was already dead or
356 *      dying when grab_super() had been called).  Note that this is only
357 *      called for superblocks not in rundown mode (== ones still on ->fs_supers
358 *      of their type), so increment of ->s_count is OK here.
359 */
360static int grab_super(struct super_block *s) __releases(sb_lock)
361{
362        s->s_count++;
363        spin_unlock(&sb_lock);
364        down_write(&s->s_umount);
365        if ((s->s_flags & MS_BORN) && atomic_inc_not_zero(&s->s_active)) {
366                put_super(s);
367                return 1;
368        }
369        up_write(&s->s_umount);
370        put_super(s);
371        return 0;
372}
373
374/*
375 *      trylock_super - try to grab ->s_umount shared
376 *      @sb: reference we are trying to grab
377 *
378 *      Try to prevent fs shutdown.  This is used in places where we
379 *      cannot take an active reference but we need to ensure that the
380 *      filesystem is not shut down while we are working on it. It returns
381 *      false if we cannot acquire s_umount or if we lose the race and
382 *      filesystem already got into shutdown, and returns true with the s_umount
383 *      lock held in read mode in case of success. On successful return,
384 *      the caller must drop the s_umount lock when done.
385 *
386 *      Note that unlike get_super() et.al. this one does *not* bump ->s_count.
387 *      The reason why it's safe is that we are OK with doing trylock instead
388 *      of down_read().  There's a couple of places that are OK with that, but
389 *      it's very much not a general-purpose interface.
390 */
391bool trylock_super(struct super_block *sb)
392{
393        if (down_read_trylock(&sb->s_umount)) {
394                if (!hlist_unhashed(&sb->s_instances) &&
395                    sb->s_root && (sb->s_flags & MS_BORN))
396                        return true;
397                up_read(&sb->s_umount);
398        }
399
400        return false;
401}
402
403/**
404 *      generic_shutdown_super  -       common helper for ->kill_sb()
405 *      @sb: superblock to kill
406 *
407 *      generic_shutdown_super() does all fs-independent work on superblock
408 *      shutdown.  Typical ->kill_sb() should pick all fs-specific objects
409 *      that need destruction out of superblock, call generic_shutdown_super()
410 *      and release aforementioned objects.  Note: dentries and inodes _are_
411 *      taken care of and do not need specific handling.
412 *
413 *      Upon calling this function, the filesystem may no longer alter or
414 *      rearrange the set of dentries belonging to this super_block, nor may it
415 *      change the attachments of dentries to inodes.
416 */
417void generic_shutdown_super(struct super_block *sb)
418{
419        const struct super_operations *sop = sb->s_op;
420
421        if (sb->s_root) {
422                shrink_dcache_for_umount(sb);
423                sync_filesystem(sb);
424                sb->s_flags &= ~MS_ACTIVE;
425
426                fsnotify_unmount_inodes(sb);
427                cgroup_writeback_umount();
428
429                evict_inodes(sb);
430
431                if (sb->s_dio_done_wq) {
432                        destroy_workqueue(sb->s_dio_done_wq);
433                        sb->s_dio_done_wq = NULL;
434                }
435
436                if (sop->put_super)
437                        sop->put_super(sb);
438
439                if (!list_empty(&sb->s_inodes)) {
440                        printk("VFS: Busy inodes after unmount of %s. "
441                           "Self-destruct in 5 seconds.  Have a nice day...\n",
442                           sb->s_id);
443                }
444        }
445        spin_lock(&sb_lock);
446        /* should be initialized for __put_super_and_need_restart() */
447        hlist_del_init(&sb->s_instances);
448        spin_unlock(&sb_lock);
449        up_write(&sb->s_umount);
450}
451
452EXPORT_SYMBOL(generic_shutdown_super);
453
454/**
455 *      sget_userns -   find or create a superblock
456 *      @type:  filesystem type superblock should belong to
457 *      @test:  comparison callback
458 *      @set:   setup callback
459 *      @flags: mount flags
460 *      @user_ns: User namespace for the super_block
461 *      @data:  argument to each of them
462 */
463struct super_block *sget_userns(struct file_system_type *type,
464                        int (*test)(struct super_block *,void *),
465                        int (*set)(struct super_block *,void *),
466                        int flags, struct user_namespace *user_ns,
467                        void *data)
468{
469        struct super_block *s = NULL;
470        struct super_block *old;
471        int err;
472
473        if (!(flags & (MS_KERNMOUNT|MS_SUBMOUNT)) &&
474            !(type->fs_flags & FS_USERNS_MOUNT) &&
475            !capable(CAP_SYS_ADMIN))
476                return ERR_PTR(-EPERM);
477retry:
478        spin_lock(&sb_lock);
479        if (test) {
480                hlist_for_each_entry(old, &type->fs_supers, s_instances) {
481                        if (!test(old, data))
482                                continue;
483                        if (user_ns != old->s_user_ns) {
484                                spin_unlock(&sb_lock);
485                                if (s) {
486                                        up_write(&s->s_umount);
487                                        destroy_super(s);
488                                }
489                                return ERR_PTR(-EBUSY);
490                        }
491                        if (!grab_super(old))
492                                goto retry;
493                        if (s) {
494                                up_write(&s->s_umount);
495                                destroy_super(s);
496                                s = NULL;
497                        }
498                        return old;
499                }
500        }
501        if (!s) {
502                spin_unlock(&sb_lock);
503                s = alloc_super(type, (flags & ~MS_SUBMOUNT), user_ns);
504                if (!s)
505                        return ERR_PTR(-ENOMEM);
506                goto retry;
507        }
508               
509        err = set(s, data);
510        if (err) {
511                spin_unlock(&sb_lock);
512                up_write(&s->s_umount);
513                destroy_super(s);
514                return ERR_PTR(err);
515        }
516        s->s_type = type;
517        strlcpy(s->s_id, type->name, sizeof(s->s_id));
518        list_add_tail(&s->s_list, &super_blocks);
519        hlist_add_head(&s->s_instances, &type->fs_supers);
520        spin_unlock(&sb_lock);
521        get_filesystem(type);
522        register_shrinker(&s->s_shrink);
523        return s;
524}
525
526EXPORT_SYMBOL(sget_userns);
527
528/**
529 *      sget    -       find or create a superblock
530 *      @type:    filesystem type superblock should belong to
531 *      @test:    comparison callback
532 *      @set:     setup callback
533 *      @flags:   mount flags
534 *      @data:    argument to each of them
535 */
536struct super_block *sget(struct file_system_type *type,
537                        int (*test)(struct super_block *,void *),
538                        int (*set)(struct super_block *,void *),
539                        int flags,
540                        void *data)
541{
542        struct user_namespace *user_ns = current_user_ns();
543
544        /* We don't yet pass the user namespace of the parent
545         * mount through to here so always use &init_user_ns
546         * until that changes.
547         */
548        if (flags & MS_SUBMOUNT)
549                user_ns = &init_user_ns;
550
551        /* Ensure the requestor has permissions over the target filesystem */
552        if (!(flags & (MS_KERNMOUNT|MS_SUBMOUNT)) && !ns_capable(user_ns, CAP_SYS_ADMIN))
553                return ERR_PTR(-EPERM);
554
555        return sget_userns(type, test, set, flags, user_ns, data);
556}
557
558EXPORT_SYMBOL(sget);
559
560void drop_super(struct super_block *sb)
561{
562        up_read(&sb->s_umount);
563        put_super(sb);
564}
565
566EXPORT_SYMBOL(drop_super);
567
568/**
569 *      iterate_supers - call function for all active superblocks
570 *      @f: function to call
571 *      @arg: argument to pass to it
572 *
573 *      Scans the superblock list and calls given function, passing it
574 *      locked superblock and given argument.
575 */
576void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
577{
578        struct super_block *sb, *p = NULL;
579
580        spin_lock(&sb_lock);
581        list_for_each_entry(sb, &super_blocks, s_list) {
582                if (hlist_unhashed(&sb->s_instances))
583                        continue;
584                sb->s_count++;
585                spin_unlock(&sb_lock);
586
587                down_read(&sb->s_umount);
588                if (sb->s_root && (sb->s_flags & MS_BORN))
589                        f(sb, arg);
590                up_read(&sb->s_umount);
591
592                spin_lock(&sb_lock);
593                if (p)
594                        __put_super(p);
595                p = sb;
596        }
597        if (p)
598                __put_super(p);
599        spin_unlock(&sb_lock);
600}
601
602/**
603 *      iterate_supers_type - call function for superblocks of given type
604 *      @type: fs type
605 *      @f: function to call
606 *      @arg: argument to pass to it
607 *
608 *      Scans the superblock list and calls given function, passing it
609 *      locked superblock and given argument.
610 */
611void iterate_supers_type(struct file_system_type *type,
612        void (*f)(struct super_block *, void *), void *arg)
613{
614        struct super_block *sb, *p = NULL;
615
616        spin_lock(&sb_lock);
617        hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
618                sb->s_count++;
619                spin_unlock(&sb_lock);
620
621                down_read(&sb->s_umount);
622                if (sb->s_root && (sb->s_flags & MS_BORN))
623                        f(sb, arg);
624                up_read(&sb->s_umount);
625
626                spin_lock(&sb_lock);
627                if (p)
628                        __put_super(p);
629                p = sb;
630        }
631        if (p)
632                __put_super(p);
633        spin_unlock(&sb_lock);
634}
635
636EXPORT_SYMBOL(iterate_supers_type);
637
638/**
639 *      get_super - get the superblock of a device
640 *      @bdev: device to get the superblock for
641 *     
642 *      Scans the superblock list and finds the superblock of the file system
643 *      mounted on the device given. %NULL is returned if no match is found.
644 */
645
646struct super_block *get_super(struct block_device *bdev)
647{
648        struct super_block *sb;
649
650        if (!bdev)
651                return NULL;
652
653        spin_lock(&sb_lock);
654rescan:
655        list_for_each_entry(sb, &super_blocks, s_list) {
656                if (hlist_unhashed(&sb->s_instances))
657                        continue;
658                if (sb->s_bdev == bdev) {
659                        sb->s_count++;
660                        spin_unlock(&sb_lock);
661                        down_read(&sb->s_umount);
662                        /* still alive? */
663                        if (sb->s_root && (sb->s_flags & MS_BORN))
664                                return sb;
665                        up_read(&sb->s_umount);
666                        /* nope, got unmounted */
667                        spin_lock(&sb_lock);
668                        __put_super(sb);
669                        goto rescan;
670                }
671        }
672        spin_unlock(&sb_lock);
673        return NULL;
674}
675
676EXPORT_SYMBOL(get_super);
677
678/**
679 *      get_super_thawed - get thawed superblock of a device
680 *      @bdev: device to get the superblock for
681 *
682 *      Scans the superblock list and finds the superblock of the file system
683 *      mounted on the device. The superblock is returned once it is thawed
684 *      (or immediately if it was not frozen). %NULL is returned if no match
685 *      is found.
686 */
687struct super_block *get_super_thawed(struct block_device *bdev)
688{
689        while (1) {
690                struct super_block *s = get_super(bdev);
691                if (!s || s->s_writers.frozen == SB_UNFROZEN)
692                        return s;
693                up_read(&s->s_umount);
694                wait_event(s->s_writers.wait_unfrozen,
695                           s->s_writers.frozen == SB_UNFROZEN);
696                put_super(s);
697        }
698}
699EXPORT_SYMBOL(get_super_thawed);
700
701/**
702 * get_active_super - get an active reference to the superblock of a device
703 * @bdev: device to get the superblock for
704 *
705 * Scans the superblock list and finds the superblock of the file system
706 * mounted on the device given.  Returns the superblock with an active
707 * reference or %NULL if none was found.
708 */
709struct super_block *get_active_super(struct block_device *bdev)
710{
711        struct super_block *sb;
712
713        if (!bdev)
714                return NULL;
715
716restart:
717        spin_lock(&sb_lock);
718        list_for_each_entry(sb, &super_blocks, s_list) {
719                if (hlist_unhashed(&sb->s_instances))
720                        continue;
721                if (sb->s_bdev == bdev) {
722                        if (!grab_super(sb))
723                                goto restart;
724                        up_write(&sb->s_umount);
725                        return sb;
726                }
727        }
728        spin_unlock(&sb_lock);
729        return NULL;
730}
731 
732struct super_block *user_get_super(dev_t dev)
733{
734        struct super_block *sb;
735
736        spin_lock(&sb_lock);
737rescan:
738        list_for_each_entry(sb, &super_blocks, s_list) {
739                if (hlist_unhashed(&sb->s_instances))
740                        continue;
741                if (sb->s_dev ==  dev) {
742                        sb->s_count++;
743                        spin_unlock(&sb_lock);
744                        down_read(&sb->s_umount);
745                        /* still alive? */
746                        if (sb->s_root && (sb->s_flags & MS_BORN))
747                                return sb;
748                        up_read(&sb->s_umount);
749                        /* nope, got unmounted */
750                        spin_lock(&sb_lock);
751                        __put_super(sb);
752                        goto rescan;
753                }
754        }
755        spin_unlock(&sb_lock);
756        return NULL;
757}
758
759/**
760 *      do_remount_sb - asks filesystem to change mount options.
761 *      @sb:    superblock in question
762 *      @flags: numeric part of options
763 *      @data:  the rest of options
764 *      @force: whether or not to force the change
765 *
766 *      Alters the mount options of a mounted file system.
767 */
768int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
769{
770        int retval;
771        int remount_ro;
772
773        if (sb->s_writers.frozen != SB_UNFROZEN)
774                return -EBUSY;
775
776#ifdef CONFIG_BLOCK
777        if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
778                return -EACCES;
779#endif
780
781        remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
782
783        if (remount_ro) {
784                if (!hlist_empty(&sb->s_pins)) {
785                        up_write(&sb->s_umount);
786                        group_pin_kill(&sb->s_pins);
787                        down_write(&sb->s_umount);
788                        if (!sb->s_root)
789                                return 0;
790                        if (sb->s_writers.frozen != SB_UNFROZEN)
791                                return -EBUSY;
792                        remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
793                }
794        }
795        shrink_dcache_sb(sb);
796
797        /* If we are remounting RDONLY and current sb is read/write,
798           make sure there are no rw files opened */
799        if (remount_ro) {
800                if (force) {
801                        sb->s_readonly_remount = 1;
802                        smp_wmb();
803                } else {
804                        retval = sb_prepare_remount_readonly(sb);
805                        if (retval)
806                                return retval;
807                }
808        }
809
810        if (sb->s_op->remount_fs) {
811                retval = sb->s_op->remount_fs(sb, &flags, data);
812                if (retval) {
813                        if (!force)
814                                goto cancel_readonly;
815                        /* If forced remount, go ahead despite any errors */
816                        WARN(1, "forced remount of a %s fs returned %i\n",
817                             sb->s_type->name, retval);
818                }
819        }
820        sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
821        /* Needs to be ordered wrt mnt_is_readonly() */
822        smp_wmb();
823        sb->s_readonly_remount = 0;
824
825        /*
826         * Some filesystems modify their metadata via some other path than the
827         * bdev buffer cache (eg. use a private mapping, or directories in
828         * pagecache, etc). Also file data modifications go via their own
829         * mappings. So If we try to mount readonly then copy the filesystem
830         * from bdev, we could get stale data, so invalidate it to give a best
831         * effort at coherency.
832         */
833        if (remount_ro && sb->s_bdev)
834                invalidate_bdev(sb->s_bdev);
835        return 0;
836
837cancel_readonly:
838        sb->s_readonly_remount = 0;
839        return retval;
840}
841
842static void do_emergency_remount(struct work_struct *work)
843{
844        struct super_block *sb, *p = NULL;
845
846        spin_lock(&sb_lock);
847        list_for_each_entry(sb, &super_blocks, s_list) {
848                if (hlist_unhashed(&sb->s_instances))
849                        continue;
850                sb->s_count++;
851                spin_unlock(&sb_lock);
852                down_write(&sb->s_umount);
853                if (sb->s_root && sb->s_bdev && (sb->s_flags & MS_BORN) &&
854                    !(sb->s_flags & MS_RDONLY)) {
855                        /*
856                         * What lock protects sb->s_flags??
857                         */
858                        do_remount_sb(sb, MS_RDONLY, NULL, 1);
859                }
860                up_write(&sb->s_umount);
861                spin_lock(&sb_lock);
862                if (p)
863                        __put_super(p);
864                p = sb;
865        }
866        if (p)
867                __put_super(p);
868        spin_unlock(&sb_lock);
869        kfree(work);
870        printk("Emergency Remount complete\n");
871}
872
873void emergency_remount(void)
874{
875        struct work_struct *work;
876
877        work = kmalloc(sizeof(*work), GFP_ATOMIC);
878        if (work) {
879                INIT_WORK(work, do_emergency_remount);
880                schedule_work(work);
881        }
882}
883
884/*
885 * Unnamed block devices are dummy devices used by virtual
886 * filesystems which don't use real block-devices.  -- jrs
887 */
888
889static DEFINE_IDA(unnamed_dev_ida);
890static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
891/* Many userspace utilities consider an FSID of 0 invalid.
892 * Always return at least 1 from get_anon_bdev.
893 */
894static int unnamed_dev_start = 1;
895
896int get_anon_bdev(dev_t *p)
897{
898        int dev;
899        int error;
900
901 retry:
902        if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
903                return -ENOMEM;
904        spin_lock(&unnamed_dev_lock);
905        error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
906        if (!error)
907                unnamed_dev_start = dev + 1;
908        spin_unlock(&unnamed_dev_lock);
909        if (error == -EAGAIN)
910                /* We raced and lost with another CPU. */
911                goto retry;
912        else if (error)
913                return -EAGAIN;
914
915        if (dev >= (1 << MINORBITS)) {
916                spin_lock(&unnamed_dev_lock);
917                ida_remove(&unnamed_dev_ida, dev);
918                if (unnamed_dev_start > dev)
919                        unnamed_dev_start = dev;
920                spin_unlock(&unnamed_dev_lock);
921                return -EMFILE;
922        }
923        *p = MKDEV(0, dev & MINORMASK);
924        return 0;
925}
926EXPORT_SYMBOL(get_anon_bdev);
927
928void free_anon_bdev(dev_t dev)
929{
930        int slot = MINOR(dev);
931        spin_lock(&unnamed_dev_lock);
932        ida_remove(&unnamed_dev_ida, slot);
933        if (slot < unnamed_dev_start)
934                unnamed_dev_start = slot;
935        spin_unlock(&unnamed_dev_lock);
936}
937EXPORT_SYMBOL(free_anon_bdev);
938
939int set_anon_super(struct super_block *s, void *data)
940{
941        return get_anon_bdev(&s->s_dev);
942}
943
944EXPORT_SYMBOL(set_anon_super);
945
946void kill_anon_super(struct super_block *sb)
947{
948        dev_t dev = sb->s_dev;
949        generic_shutdown_super(sb);
950        free_anon_bdev(dev);
951}
952
953EXPORT_SYMBOL(kill_anon_super);
954
955void kill_litter_super(struct super_block *sb)
956{
957        if (sb->s_root)
958                d_genocide(sb->s_root);
959        kill_anon_super(sb);
960}
961
962EXPORT_SYMBOL(kill_litter_super);
963
964static int ns_test_super(struct super_block *sb, void *data)
965{
966        return sb->s_fs_info == data;
967}
968
969static int ns_set_super(struct super_block *sb, void *data)
970{
971        sb->s_fs_info = data;
972        return set_anon_super(sb, NULL);
973}
974
975struct dentry *mount_ns(struct file_system_type *fs_type,
976        int flags, void *data, void *ns, struct user_namespace *user_ns,
977        int (*fill_super)(struct super_block *, void *, int))
978{
979        struct super_block *sb;
980
981        /* Don't allow mounting unless the caller has CAP_SYS_ADMIN
982         * over the namespace.
983         */
984        if (!(flags & MS_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN))
985                return ERR_PTR(-EPERM);
986
987        sb = sget_userns(fs_type, ns_test_super, ns_set_super, flags,
988                         user_ns, ns);
989        if (IS_ERR(sb))
990                return ERR_CAST(sb);
991
992        if (!sb->s_root) {
993                int err;
994                err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
995                if (err) {
996                        deactivate_locked_super(sb);
997                        return ERR_PTR(err);
998                }
999
1000                sb->s_flags |= MS_ACTIVE;
1001        }
1002
1003        return dget(sb->s_root);
1004}
1005
1006EXPORT_SYMBOL(mount_ns);
1007
1008#ifdef CONFIG_BLOCK
1009static int set_bdev_super(struct super_block *s, void *data)
1010{
1011        s->s_bdev = data;
1012        s->s_dev = s->s_bdev->bd_dev;
1013
1014        /*
1015         * We set the bdi here to the queue backing, file systems can
1016         * overwrite this in ->fill_super()
1017         */
1018        s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
1019        return 0;
1020}
1021
1022static int test_bdev_super(struct super_block *s, void *data)
1023{
1024        return (void *)s->s_bdev == data;
1025}
1026
1027struct dentry *mount_bdev(struct file_system_type *fs_type,
1028        int flags, const char *dev_name, void *data,
1029        int (*fill_super)(struct super_block *, void *, int))
1030{
1031        struct block_device *bdev;
1032        struct super_block *s;
1033        fmode_t mode = FMODE_READ | FMODE_EXCL;
1034        int error = 0;
1035
1036        if (!(flags & MS_RDONLY))
1037                mode |= FMODE_WRITE;
1038
1039        bdev = blkdev_get_by_path(dev_name, mode, fs_type);
1040        if (IS_ERR(bdev))
1041                return ERR_CAST(bdev);
1042
1043        /*
1044         * once the super is inserted into the list by sget, s_umount
1045         * will protect the lockfs code from trying to start a snapshot
1046         * while we are mounting
1047         */
1048        mutex_lock(&bdev->bd_fsfreeze_mutex);
1049        if (bdev->bd_fsfreeze_count > 0) {
1050                mutex_unlock(&bdev->bd_fsfreeze_mutex);
1051                error = -EBUSY;
1052                goto error_bdev;
1053        }
1054        s = sget(fs_type, test_bdev_super, set_bdev_super, flags | MS_NOSEC,
1055                 bdev);
1056        mutex_unlock(&bdev->bd_fsfreeze_mutex);
1057        if (IS_ERR(s))
1058                goto error_s;
1059
1060        if (s->s_root) {
1061                if ((flags ^ s->s_flags) & MS_RDONLY) {
1062                        deactivate_locked_super(s);
1063                        error = -EBUSY;
1064                        goto error_bdev;
1065                }
1066
1067                /*
1068                 * s_umount nests inside bd_mutex during
1069                 * __invalidate_device().  blkdev_put() acquires
1070                 * bd_mutex and can't be called under s_umount.  Drop
1071                 * s_umount temporarily.  This is safe as we're
1072                 * holding an active reference.
1073                 */
1074                up_write(&s->s_umount);
1075                blkdev_put(bdev, mode);
1076                down_write(&s->s_umount);
1077        } else {
1078                s->s_mode = mode;
1079                snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1080                sb_set_blocksize(s, block_size(bdev));
1081                error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1082                if (error) {
1083                        deactivate_locked_super(s);
1084                        goto error;
1085                }
1086
1087                s->s_flags |= MS_ACTIVE;
1088                bdev->bd_super = s;
1089        }
1090
1091        return dget(s->s_root);
1092
1093error_s:
1094        error = PTR_ERR(s);
1095error_bdev:
1096        blkdev_put(bdev, mode);
1097error:
1098        return ERR_PTR(error);
1099}
1100EXPORT_SYMBOL(mount_bdev);
1101
1102void kill_block_super(struct super_block *sb)
1103{
1104        struct block_device *bdev = sb->s_bdev;
1105        fmode_t mode = sb->s_mode;
1106
1107        bdev->bd_super = NULL;
1108        generic_shutdown_super(sb);
1109        sync_blockdev(bdev);
1110        WARN_ON_ONCE(!(mode & FMODE_EXCL));
1111        blkdev_put(bdev, mode | FMODE_EXCL);
1112}
1113
1114EXPORT_SYMBOL(kill_block_super);
1115#endif
1116
1117struct dentry *mount_nodev(struct file_system_type *fs_type,
1118        int flags, void *data,
1119        int (*fill_super)(struct super_block *, void *, int))
1120{
1121        int error;
1122        struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1123
1124        if (IS_ERR(s))
1125                return ERR_CAST(s);
1126
1127        error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1128        if (error) {
1129                deactivate_locked_super(s);
1130                return ERR_PTR(error);
1131        }
1132        s->s_flags |= MS_ACTIVE;
1133        return dget(s->s_root);
1134}
1135EXPORT_SYMBOL(mount_nodev);
1136
1137static int compare_single(struct super_block *s, void *p)
1138{
1139        return 1;
1140}
1141
1142struct dentry *mount_single(struct file_system_type *fs_type,
1143        int flags, void *data,
1144        int (*fill_super)(struct super_block *, void *, int))
1145{
1146        struct super_block *s;
1147        int error;
1148
1149        s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1150        if (IS_ERR(s))
1151                return ERR_CAST(s);
1152        if (!s->s_root) {
1153                error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1154                if (error) {
1155                        deactivate_locked_super(s);
1156                        return ERR_PTR(error);
1157                }
1158                s->s_flags |= MS_ACTIVE;
1159        } else {
1160                do_remount_sb(s, flags, data, 0);
1161        }
1162        return dget(s->s_root);
1163}
1164EXPORT_SYMBOL(mount_single);
1165
1166struct dentry *
1167mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
1168{
1169        struct dentry *root;
1170        struct super_block *sb;
1171        char *secdata = NULL;
1172        int error = -ENOMEM;
1173
1174        if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
1175                secdata = alloc_secdata();
1176                if (!secdata)
1177                        goto out;
1178
1179                error = security_sb_copy_data(data, secdata);
1180                if (error)
1181                        goto out_free_secdata;
1182        }
1183
1184        root = type->mount(type, flags, name, data);
1185        if (IS_ERR(root)) {
1186                error = PTR_ERR(root);
1187                goto out_free_secdata;
1188        }
1189        sb = root->d_sb;
1190        BUG_ON(!sb);
1191        WARN_ON(!sb->s_bdi);
1192        sb->s_flags |= MS_BORN;
1193
1194        error = security_sb_kern_mount(sb, flags, secdata);
1195        if (error)
1196                goto out_sb;
1197
1198        /*
1199         * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1200         * but s_maxbytes was an unsigned long long for many releases. Throw
1201         * this warning for a little while to try and catch filesystems that
1202         * violate this rule.
1203         */
1204        WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1205                "negative value (%lld)\n", type->name, sb->s_maxbytes);
1206
1207        up_write(&sb->s_umount);
1208        free_secdata(secdata);
1209        return root;
1210out_sb:
1211        dput(root);
1212        deactivate_locked_super(sb);
1213out_free_secdata:
1214        free_secdata(secdata);
1215out:
1216        return ERR_PTR(error);
1217}
1218
1219/*
1220 * This is an internal function, please use sb_end_{write,pagefault,intwrite}
1221 * instead.
1222 */
1223void __sb_end_write(struct super_block *sb, int level)
1224{
1225        percpu_up_read(sb->s_writers.rw_sem + level-1);
1226}
1227EXPORT_SYMBOL(__sb_end_write);
1228
1229/*
1230 * This is an internal function, please use sb_start_{write,pagefault,intwrite}
1231 * instead.
1232 */
1233int __sb_start_write(struct super_block *sb, int level, bool wait)
1234{
1235        bool force_trylock = false;
1236        int ret = 1;
1237
1238#ifdef CONFIG_LOCKDEP
1239        /*
1240         * We want lockdep to tell us about possible deadlocks with freezing
1241         * but it's it bit tricky to properly instrument it. Getting a freeze
1242         * protection works as getting a read lock but there are subtle
1243         * problems. XFS for example gets freeze protection on internal level
1244         * twice in some cases, which is OK only because we already hold a
1245         * freeze protection also on higher level. Due to these cases we have
1246         * to use wait == F (trylock mode) which must not fail.
1247         */
1248        if (wait) {
1249                int i;
1250
1251                for (i = 0; i < level - 1; i++)
1252                        if (percpu_rwsem_is_held(sb->s_writers.rw_sem + i)) {
1253                                force_trylock = true;
1254                                break;
1255                        }
1256        }
1257#endif
1258        if (wait && !force_trylock)
1259                percpu_down_read(sb->s_writers.rw_sem + level-1);
1260        else
1261                ret = percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
1262
1263        WARN_ON(force_trylock && !ret);
1264        return ret;
1265}
1266EXPORT_SYMBOL(__sb_start_write);
1267
1268/**
1269 * sb_wait_write - wait until all writers to given file system finish
1270 * @sb: the super for which we wait
1271 * @level: type of writers we wait for (normal vs page fault)
1272 *
1273 * This function waits until there are no writers of given type to given file
1274 * system.
1275 */
1276static void sb_wait_write(struct super_block *sb, int level)
1277{
1278        percpu_down_write(sb->s_writers.rw_sem + level-1);
1279}
1280
1281/*
1282 * We are going to return to userspace and forget about these locks, the
1283 * ownership goes to the caller of thaw_super() which does unlock().
1284 */
1285static void lockdep_sb_freeze_release(struct super_block *sb)
1286{
1287        int level;
1288
1289        for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1290                percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1291}
1292
1293/*
1294 * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
1295 */
1296static void lockdep_sb_freeze_acquire(struct super_block *sb)
1297{
1298        int level;
1299
1300        for (level = 0; level < SB_FREEZE_LEVELS; ++level)
1301                percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1302}
1303
1304static void sb_freeze_unlock(struct super_block *sb)
1305{
1306        int level;
1307
1308        for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1309                percpu_up_write(sb->s_writers.rw_sem + level);
1310}
1311
1312/**
1313 * freeze_super - lock the filesystem and force it into a consistent state
1314 * @sb: the super to lock
1315 *
1316 * Syncs the super to make sure the filesystem is consistent and calls the fs's
1317 * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1318 * -EBUSY.
1319 *
1320 * During this function, sb->s_writers.frozen goes through these values:
1321 *
1322 * SB_UNFROZEN: File system is normal, all writes progress as usual.
1323 *
1324 * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
1325 * writes should be blocked, though page faults are still allowed. We wait for
1326 * all writes to complete and then proceed to the next stage.
1327 *
1328 * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1329 * but internal fs threads can still modify the filesystem (although they
1330 * should not dirty new pages or inodes), writeback can run etc. After waiting
1331 * for all running page faults we sync the filesystem which will clean all
1332 * dirty pages and inodes (no new dirty pages or inodes can be created when
1333 * sync is running).
1334 *
1335 * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1336 * modification are blocked (e.g. XFS preallocation truncation on inode
1337 * reclaim). This is usually implemented by blocking new transactions for
1338 * filesystems that have them and need this additional guard. After all
1339 * internal writers are finished we call ->freeze_fs() to finish filesystem
1340 * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1341 * mostly auxiliary for filesystems to verify they do not modify frozen fs.
1342 *
1343 * sb->s_writers.frozen is protected by sb->s_umount.
1344 */
1345int freeze_super(struct super_block *sb)
1346{
1347        int ret;
1348
1349        atomic_inc(&sb->s_active);
1350        down_write(&sb->s_umount);
1351        if (sb->s_writers.frozen != SB_UNFROZEN) {
1352                deactivate_locked_super(sb);
1353                return -EBUSY;
1354        }
1355
1356        if (!(sb->s_flags & MS_BORN)) {
1357                up_write(&sb->s_umount);
1358                return 0;       /* sic - it's "nothing to do" */
1359        }
1360
1361        if (sb->s_flags & MS_RDONLY) {
1362                /* Nothing to do really... */
1363                sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1364                up_write(&sb->s_umount);
1365                return 0;
1366        }
1367
1368        sb->s_writers.frozen = SB_FREEZE_WRITE;
1369        /* Release s_umount to preserve sb_start_write -> s_umount ordering */
1370        up_write(&sb->s_umount);
1371        sb_wait_write(sb, SB_FREEZE_WRITE);
1372        down_write(&sb->s_umount);
1373
1374        /* Now we go and block page faults... */
1375        sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1376        sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1377
1378        /* All writers are done so after syncing there won't be dirty data */
1379        sync_filesystem(sb);
1380
1381        /* Now wait for internal filesystem counter */
1382        sb->s_writers.frozen = SB_FREEZE_FS;
1383        sb_wait_write(sb, SB_FREEZE_FS);
1384
1385        if (sb->s_op->freeze_fs) {
1386                ret = sb->s_op->freeze_fs(sb);
1387                if (ret) {
1388                        printk(KERN_ERR
1389                                "VFS:Filesystem freeze failed\n");
1390                        sb->s_writers.frozen = SB_UNFROZEN;
1391                        sb_freeze_unlock(sb);
1392                        wake_up(&sb->s_writers.wait_unfrozen);
1393                        deactivate_locked_super(sb);
1394                        return ret;
1395                }
1396        }
1397        /*
1398         * For debugging purposes so that fs can warn if it sees write activity
1399         * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
1400         */
1401        sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1402        lockdep_sb_freeze_release(sb);
1403        up_write(&sb->s_umount);
1404        return 0;
1405}
1406EXPORT_SYMBOL(freeze_super);
1407
1408/**
1409 * thaw_super -- unlock filesystem
1410 * @sb: the super to thaw
1411 *
1412 * Unlocks the filesystem and marks it writeable again after freeze_super().
1413 */
1414int thaw_super(struct super_block *sb)
1415{
1416        int error;
1417
1418        down_write(&sb->s_umount);
1419        if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
1420                up_write(&sb->s_umount);
1421                return -EINVAL;
1422        }
1423
1424        if (sb->s_flags & MS_RDONLY) {
1425                sb->s_writers.frozen = SB_UNFROZEN;
1426                goto out;
1427        }
1428
1429        lockdep_sb_freeze_acquire(sb);
1430
1431        if (sb->s_op->unfreeze_fs) {
1432                error = sb->s_op->unfreeze_fs(sb);
1433                if (error) {
1434                        printk(KERN_ERR
1435                                "VFS:Filesystem thaw failed\n");
1436                        lockdep_sb_freeze_release(sb);
1437                        up_write(&sb->s_umount);
1438                        return error;
1439                }
1440        }
1441
1442        sb->s_writers.frozen = SB_UNFROZEN;
1443        sb_freeze_unlock(sb);
1444out:
1445        wake_up(&sb->s_writers.wait_unfrozen);
1446        deactivate_locked_super(sb);
1447        return 0;
1448}
1449EXPORT_SYMBOL(thaw_super);
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