4 * Copyright (C) 1991, 1992 Linus Torvalds
6 * super.c contains code to handle: - mount structures
8 * - filesystem drivers list
10 * - umount system call
13 * GK 2/5/95 - Changed to support mounting the root fs via NFS
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
23 #include <linux/module.h>
24 #include <linux/slab.h>
25 #include <linux/acct.h>
26 #include <linux/blkdev.h>
27 #include <linux/mount.h>
28 #include <linux/security.h>
29 #include <linux/writeback.h> /* for the emergency remount stuff */
30 #include <linux/idr.h>
31 #include <linux/mutex.h>
32 #include <linux/backing-dev.h>
33 #include <linux/rculist_bl.h>
34 #include <linux/cleancache.h>
38 LIST_HEAD(super_blocks);
39 DEFINE_SPINLOCK(sb_lock);
42 * alloc_super - create new superblock
43 * @type: filesystem type superblock should belong to
45 * Allocates and initializes a new &struct super_block. alloc_super()
46 * returns a pointer new superblock or %NULL if allocation had failed.
48 static struct super_block *alloc_super(struct file_system_type *type)
50 struct super_block *s = kzalloc(sizeof(struct super_block), GFP_USER);
51 static const struct super_operations default_op;
54 if (security_sb_alloc(s)) {
60 s->s_files = alloc_percpu(struct list_head);
69 for_each_possible_cpu(i)
70 INIT_LIST_HEAD(per_cpu_ptr(s->s_files, i));
73 INIT_LIST_HEAD(&s->s_files);
75 s->s_bdi = &default_backing_dev_info;
76 INIT_LIST_HEAD(&s->s_instances);
77 INIT_HLIST_BL_HEAD(&s->s_anon);
78 INIT_LIST_HEAD(&s->s_inodes);
79 INIT_LIST_HEAD(&s->s_dentry_lru);
80 INIT_LIST_HEAD(&s->s_inode_lru);
81 init_rwsem(&s->s_umount);
82 mutex_init(&s->s_lock);
83 lockdep_set_class(&s->s_umount, &type->s_umount_key);
85 * The locking rules for s_lock are up to the
86 * filesystem. For example ext3fs has different
87 * lock ordering than usbfs:
89 lockdep_set_class(&s->s_lock, &type->s_lock_key);
91 * sget() can have s_umount recursion.
93 * When it cannot find a suitable sb, it allocates a new
94 * one (this one), and tries again to find a suitable old
97 * In case that succeeds, it will acquire the s_umount
98 * lock of the old one. Since these are clearly distrinct
99 * locks, and this object isn't exposed yet, there's no
102 * Annotate this by putting this lock in a different
105 down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
107 atomic_set(&s->s_active, 1);
108 mutex_init(&s->s_vfs_rename_mutex);
109 lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
110 mutex_init(&s->s_dquot.dqio_mutex);
111 mutex_init(&s->s_dquot.dqonoff_mutex);
112 init_rwsem(&s->s_dquot.dqptr_sem);
113 init_waitqueue_head(&s->s_wait_unfrozen);
114 s->s_maxbytes = MAX_NON_LFS;
115 s->s_op = &default_op;
116 s->s_time_gran = 1000000000;
117 s->cleancache_poolid = -1;
124 * destroy_super - frees a superblock
125 * @s: superblock to free
127 * Frees a superblock.
129 static inline void destroy_super(struct super_block *s)
132 free_percpu(s->s_files);
140 /* Superblock refcounting */
143 * Drop a superblock's refcount. The caller must hold sb_lock.
145 void __put_super(struct super_block *sb)
147 if (!--sb->s_count) {
148 list_del_init(&sb->s_list);
154 * put_super - drop a temporary reference to superblock
155 * @sb: superblock in question
157 * Drops a temporary reference, frees superblock if there's no
160 void put_super(struct super_block *sb)
164 spin_unlock(&sb_lock);
169 * deactivate_locked_super - drop an active reference to superblock
170 * @s: superblock to deactivate
172 * Drops an active reference to superblock, converting it into a temprory
173 * one if there is no other active references left. In that case we
174 * tell fs driver to shut it down and drop the temporary reference we
177 * Caller holds exclusive lock on superblock; that lock is released.
179 void deactivate_locked_super(struct super_block *s)
181 struct file_system_type *fs = s->s_type;
182 if (atomic_dec_and_test(&s->s_active)) {
183 cleancache_flush_fs(s);
186 * We need to call rcu_barrier so all the delayed rcu free
187 * inodes are flushed before we release the fs module.
193 up_write(&s->s_umount);
197 EXPORT_SYMBOL(deactivate_locked_super);
200 * deactivate_super - drop an active reference to superblock
201 * @s: superblock to deactivate
203 * Variant of deactivate_locked_super(), except that superblock is *not*
204 * locked by caller. If we are going to drop the final active reference,
205 * lock will be acquired prior to that.
207 void deactivate_super(struct super_block *s)
209 if (!atomic_add_unless(&s->s_active, -1, 1)) {
210 down_write(&s->s_umount);
211 deactivate_locked_super(s);
215 EXPORT_SYMBOL(deactivate_super);
218 * grab_super - acquire an active reference
219 * @s: reference we are trying to make active
221 * Tries to acquire an active reference. grab_super() is used when we
222 * had just found a superblock in super_blocks or fs_type->fs_supers
223 * and want to turn it into a full-blown active reference. grab_super()
224 * is called with sb_lock held and drops it. Returns 1 in case of
225 * success, 0 if we had failed (superblock contents was already dead or
226 * dying when grab_super() had been called).
228 static int grab_super(struct super_block *s) __releases(sb_lock)
230 if (atomic_inc_not_zero(&s->s_active)) {
231 spin_unlock(&sb_lock);
234 /* it's going away */
236 spin_unlock(&sb_lock);
237 /* wait for it to die */
238 down_write(&s->s_umount);
239 up_write(&s->s_umount);
245 * Superblock locking. We really ought to get rid of these two.
247 void lock_super(struct super_block * sb)
250 mutex_lock(&sb->s_lock);
253 void unlock_super(struct super_block * sb)
256 mutex_unlock(&sb->s_lock);
259 EXPORT_SYMBOL(lock_super);
260 EXPORT_SYMBOL(unlock_super);
263 * generic_shutdown_super - common helper for ->kill_sb()
264 * @sb: superblock to kill
266 * generic_shutdown_super() does all fs-independent work on superblock
267 * shutdown. Typical ->kill_sb() should pick all fs-specific objects
268 * that need destruction out of superblock, call generic_shutdown_super()
269 * and release aforementioned objects. Note: dentries and inodes _are_
270 * taken care of and do not need specific handling.
272 * Upon calling this function, the filesystem may no longer alter or
273 * rearrange the set of dentries belonging to this super_block, nor may it
274 * change the attachments of dentries to inodes.
276 void generic_shutdown_super(struct super_block *sb)
278 const struct super_operations *sop = sb->s_op;
282 shrink_dcache_for_umount(sb);
285 sb->s_flags &= ~MS_ACTIVE;
287 fsnotify_unmount_inodes(&sb->s_inodes);
294 if (!list_empty(&sb->s_inodes)) {
295 printk("VFS: Busy inodes after unmount of %s. "
296 "Self-destruct in 5 seconds. Have a nice day...\n",
302 /* should be initialized for __put_super_and_need_restart() */
303 list_del_init(&sb->s_instances);
304 spin_unlock(&sb_lock);
305 up_write(&sb->s_umount);
308 EXPORT_SYMBOL(generic_shutdown_super);
311 * sget - find or create a superblock
312 * @type: filesystem type superblock should belong to
313 * @test: comparison callback
314 * @set: setup callback
315 * @data: argument to each of them
317 struct super_block *sget(struct file_system_type *type,
318 int (*test)(struct super_block *,void *),
319 int (*set)(struct super_block *,void *),
322 struct super_block *s = NULL;
323 struct super_block *old;
329 list_for_each_entry(old, &type->fs_supers, s_instances) {
330 if (!test(old, data))
332 if (!grab_super(old))
335 up_write(&s->s_umount);
339 down_write(&old->s_umount);
340 if (unlikely(!(old->s_flags & MS_BORN))) {
341 deactivate_locked_super(old);
348 spin_unlock(&sb_lock);
349 s = alloc_super(type);
351 return ERR_PTR(-ENOMEM);
357 spin_unlock(&sb_lock);
358 up_write(&s->s_umount);
363 strlcpy(s->s_id, type->name, sizeof(s->s_id));
364 list_add_tail(&s->s_list, &super_blocks);
365 list_add(&s->s_instances, &type->fs_supers);
366 spin_unlock(&sb_lock);
367 get_filesystem(type);
373 void drop_super(struct super_block *sb)
375 up_read(&sb->s_umount);
379 EXPORT_SYMBOL(drop_super);
382 * sync_supers - helper for periodic superblock writeback
384 * Call the write_super method if present on all dirty superblocks in
385 * the system. This is for the periodic writeback used by most older
386 * filesystems. For data integrity superblock writeback use
387 * sync_filesystems() instead.
389 * Note: check the dirty flag before waiting, so we don't
390 * hold up the sync while mounting a device. (The newly
391 * mounted device won't need syncing.)
393 void sync_supers(void)
395 struct super_block *sb, *p = NULL;
398 list_for_each_entry(sb, &super_blocks, s_list) {
399 if (list_empty(&sb->s_instances))
401 if (sb->s_op->write_super && sb->s_dirt) {
403 spin_unlock(&sb_lock);
405 down_read(&sb->s_umount);
406 if (sb->s_root && sb->s_dirt)
407 sb->s_op->write_super(sb);
408 up_read(&sb->s_umount);
418 spin_unlock(&sb_lock);
422 * iterate_supers - call function for all active superblocks
423 * @f: function to call
424 * @arg: argument to pass to it
426 * Scans the superblock list and calls given function, passing it
427 * locked superblock and given argument.
429 void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
431 struct super_block *sb, *p = NULL;
434 list_for_each_entry(sb, &super_blocks, s_list) {
435 if (list_empty(&sb->s_instances))
438 spin_unlock(&sb_lock);
440 down_read(&sb->s_umount);
443 up_read(&sb->s_umount);
452 spin_unlock(&sb_lock);
456 * iterate_supers_type - call function for superblocks of given type
458 * @f: function to call
459 * @arg: argument to pass to it
461 * Scans the superblock list and calls given function, passing it
462 * locked superblock and given argument.
464 void iterate_supers_type(struct file_system_type *type,
465 void (*f)(struct super_block *, void *), void *arg)
467 struct super_block *sb, *p = NULL;
470 list_for_each_entry(sb, &type->fs_supers, s_instances) {
472 spin_unlock(&sb_lock);
474 down_read(&sb->s_umount);
477 up_read(&sb->s_umount);
486 spin_unlock(&sb_lock);
489 EXPORT_SYMBOL(iterate_supers_type);
492 * get_super - get the superblock of a device
493 * @bdev: device to get the superblock for
495 * Scans the superblock list and finds the superblock of the file system
496 * mounted on the device given. %NULL is returned if no match is found.
499 struct super_block *get_super(struct block_device *bdev)
501 struct super_block *sb;
508 list_for_each_entry(sb, &super_blocks, s_list) {
509 if (list_empty(&sb->s_instances))
511 if (sb->s_bdev == bdev) {
513 spin_unlock(&sb_lock);
514 down_read(&sb->s_umount);
518 up_read(&sb->s_umount);
519 /* nope, got unmounted */
525 spin_unlock(&sb_lock);
529 EXPORT_SYMBOL(get_super);
532 * get_active_super - get an active reference to the superblock of a device
533 * @bdev: device to get the superblock for
535 * Scans the superblock list and finds the superblock of the file system
536 * mounted on the device given. Returns the superblock with an active
537 * reference or %NULL if none was found.
539 struct super_block *get_active_super(struct block_device *bdev)
541 struct super_block *sb;
548 list_for_each_entry(sb, &super_blocks, s_list) {
549 if (list_empty(&sb->s_instances))
551 if (sb->s_bdev == bdev) {
552 if (grab_super(sb)) /* drops sb_lock */
558 spin_unlock(&sb_lock);
562 struct super_block *user_get_super(dev_t dev)
564 struct super_block *sb;
568 list_for_each_entry(sb, &super_blocks, s_list) {
569 if (list_empty(&sb->s_instances))
571 if (sb->s_dev == dev) {
573 spin_unlock(&sb_lock);
574 down_read(&sb->s_umount);
578 up_read(&sb->s_umount);
579 /* nope, got unmounted */
585 spin_unlock(&sb_lock);
590 * do_remount_sb - asks filesystem to change mount options.
591 * @sb: superblock in question
592 * @flags: numeric part of options
593 * @data: the rest of options
594 * @force: whether or not to force the change
596 * Alters the mount options of a mounted file system.
598 int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
603 if (sb->s_frozen != SB_UNFROZEN)
607 if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
611 if (flags & MS_RDONLY)
613 shrink_dcache_sb(sb);
616 remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
618 /* If we are remounting RDONLY and current sb is read/write,
619 make sure there are no rw files opened */
623 else if (!fs_may_remount_ro(sb))
627 if (sb->s_op->remount_fs) {
628 retval = sb->s_op->remount_fs(sb, &flags, data);
632 sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
635 * Some filesystems modify their metadata via some other path than the
636 * bdev buffer cache (eg. use a private mapping, or directories in
637 * pagecache, etc). Also file data modifications go via their own
638 * mappings. So If we try to mount readonly then copy the filesystem
639 * from bdev, we could get stale data, so invalidate it to give a best
640 * effort at coherency.
642 if (remount_ro && sb->s_bdev)
643 invalidate_bdev(sb->s_bdev);
647 static void do_emergency_remount(struct work_struct *work)
649 struct super_block *sb, *p = NULL;
652 list_for_each_entry(sb, &super_blocks, s_list) {
653 if (list_empty(&sb->s_instances))
656 spin_unlock(&sb_lock);
657 down_write(&sb->s_umount);
658 if (sb->s_root && sb->s_bdev && !(sb->s_flags & MS_RDONLY)) {
660 * What lock protects sb->s_flags??
662 do_remount_sb(sb, MS_RDONLY, NULL, 1);
664 up_write(&sb->s_umount);
672 spin_unlock(&sb_lock);
674 printk("Emergency Remount complete\n");
677 void emergency_remount(void)
679 struct work_struct *work;
681 work = kmalloc(sizeof(*work), GFP_ATOMIC);
683 INIT_WORK(work, do_emergency_remount);
689 * Unnamed block devices are dummy devices used by virtual
690 * filesystems which don't use real block-devices. -- jrs
693 static DEFINE_IDA(unnamed_dev_ida);
694 static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
695 static int unnamed_dev_start = 0; /* don't bother trying below it */
697 int get_anon_bdev(dev_t *p)
703 if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
705 spin_lock(&unnamed_dev_lock);
706 error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
708 unnamed_dev_start = dev + 1;
709 spin_unlock(&unnamed_dev_lock);
710 if (error == -EAGAIN)
711 /* We raced and lost with another CPU. */
716 if ((dev & MAX_ID_MASK) == (1 << MINORBITS)) {
717 spin_lock(&unnamed_dev_lock);
718 ida_remove(&unnamed_dev_ida, dev);
719 if (unnamed_dev_start > dev)
720 unnamed_dev_start = dev;
721 spin_unlock(&unnamed_dev_lock);
724 *p = MKDEV(0, dev & MINORMASK);
727 EXPORT_SYMBOL(get_anon_bdev);
729 void free_anon_bdev(dev_t dev)
731 int slot = MINOR(dev);
732 spin_lock(&unnamed_dev_lock);
733 ida_remove(&unnamed_dev_ida, slot);
734 if (slot < unnamed_dev_start)
735 unnamed_dev_start = slot;
736 spin_unlock(&unnamed_dev_lock);
738 EXPORT_SYMBOL(free_anon_bdev);
740 int set_anon_super(struct super_block *s, void *data)
742 int error = get_anon_bdev(&s->s_dev);
744 s->s_bdi = &noop_backing_dev_info;
748 EXPORT_SYMBOL(set_anon_super);
750 void kill_anon_super(struct super_block *sb)
752 dev_t dev = sb->s_dev;
753 generic_shutdown_super(sb);
757 EXPORT_SYMBOL(kill_anon_super);
759 void kill_litter_super(struct super_block *sb)
762 d_genocide(sb->s_root);
766 EXPORT_SYMBOL(kill_litter_super);
768 static int ns_test_super(struct super_block *sb, void *data)
770 return sb->s_fs_info == data;
773 static int ns_set_super(struct super_block *sb, void *data)
775 sb->s_fs_info = data;
776 return set_anon_super(sb, NULL);
779 struct dentry *mount_ns(struct file_system_type *fs_type, int flags,
780 void *data, int (*fill_super)(struct super_block *, void *, int))
782 struct super_block *sb;
784 sb = sget(fs_type, ns_test_super, ns_set_super, data);
791 err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
793 deactivate_locked_super(sb);
797 sb->s_flags |= MS_ACTIVE;
800 return dget(sb->s_root);
803 EXPORT_SYMBOL(mount_ns);
806 static int set_bdev_super(struct super_block *s, void *data)
809 s->s_dev = s->s_bdev->bd_dev;
812 * We set the bdi here to the queue backing, file systems can
813 * overwrite this in ->fill_super()
815 s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
819 static int test_bdev_super(struct super_block *s, void *data)
821 return (void *)s->s_bdev == data;
824 struct dentry *mount_bdev(struct file_system_type *fs_type,
825 int flags, const char *dev_name, void *data,
826 int (*fill_super)(struct super_block *, void *, int))
828 struct block_device *bdev;
829 struct super_block *s;
830 fmode_t mode = FMODE_READ | FMODE_EXCL;
833 if (!(flags & MS_RDONLY))
836 bdev = blkdev_get_by_path(dev_name, mode, fs_type);
838 return ERR_CAST(bdev);
841 * once the super is inserted into the list by sget, s_umount
842 * will protect the lockfs code from trying to start a snapshot
843 * while we are mounting
845 mutex_lock(&bdev->bd_fsfreeze_mutex);
846 if (bdev->bd_fsfreeze_count > 0) {
847 mutex_unlock(&bdev->bd_fsfreeze_mutex);
851 s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
852 mutex_unlock(&bdev->bd_fsfreeze_mutex);
857 if ((flags ^ s->s_flags) & MS_RDONLY) {
858 deactivate_locked_super(s);
864 * s_umount nests inside bd_mutex during
865 * __invalidate_device(). blkdev_put() acquires
866 * bd_mutex and can't be called under s_umount. Drop
867 * s_umount temporarily. This is safe as we're
868 * holding an active reference.
870 up_write(&s->s_umount);
871 blkdev_put(bdev, mode);
872 down_write(&s->s_umount);
874 char b[BDEVNAME_SIZE];
876 s->s_flags = flags | MS_NOSEC;
878 strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
879 sb_set_blocksize(s, block_size(bdev));
880 error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
882 deactivate_locked_super(s);
886 s->s_flags |= MS_ACTIVE;
890 return dget(s->s_root);
895 blkdev_put(bdev, mode);
897 return ERR_PTR(error);
899 EXPORT_SYMBOL(mount_bdev);
901 void kill_block_super(struct super_block *sb)
903 struct block_device *bdev = sb->s_bdev;
904 fmode_t mode = sb->s_mode;
906 bdev->bd_super = NULL;
907 generic_shutdown_super(sb);
909 WARN_ON_ONCE(!(mode & FMODE_EXCL));
910 blkdev_put(bdev, mode | FMODE_EXCL);
913 EXPORT_SYMBOL(kill_block_super);
916 struct dentry *mount_nodev(struct file_system_type *fs_type,
917 int flags, void *data,
918 int (*fill_super)(struct super_block *, void *, int))
921 struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);
928 error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
930 deactivate_locked_super(s);
931 return ERR_PTR(error);
933 s->s_flags |= MS_ACTIVE;
934 return dget(s->s_root);
936 EXPORT_SYMBOL(mount_nodev);
938 static int compare_single(struct super_block *s, void *p)
943 struct dentry *mount_single(struct file_system_type *fs_type,
944 int flags, void *data,
945 int (*fill_super)(struct super_block *, void *, int))
947 struct super_block *s;
950 s = sget(fs_type, compare_single, set_anon_super, NULL);
955 error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
957 deactivate_locked_super(s);
958 return ERR_PTR(error);
960 s->s_flags |= MS_ACTIVE;
962 do_remount_sb(s, flags, data, 0);
964 return dget(s->s_root);
966 EXPORT_SYMBOL(mount_single);
969 mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
972 struct super_block *sb;
973 char *secdata = NULL;
976 if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
977 secdata = alloc_secdata();
981 error = security_sb_copy_data(data, secdata);
983 goto out_free_secdata;
986 root = type->mount(type, flags, name, data);
988 error = PTR_ERR(root);
989 goto out_free_secdata;
994 WARN_ON(sb->s_bdi == &default_backing_dev_info);
995 sb->s_flags |= MS_BORN;
997 error = security_sb_kern_mount(sb, flags, secdata);
1002 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1003 * but s_maxbytes was an unsigned long long for many releases. Throw
1004 * this warning for a little while to try and catch filesystems that
1005 * violate this rule.
1007 WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1008 "negative value (%lld)\n", type->name, sb->s_maxbytes);
1010 up_write(&sb->s_umount);
1011 free_secdata(secdata);
1015 deactivate_locked_super(sb);
1017 free_secdata(secdata);
1019 return ERR_PTR(error);
1023 * freeze_super - lock the filesystem and force it into a consistent state
1024 * @sb: the super to lock
1026 * Syncs the super to make sure the filesystem is consistent and calls the fs's
1027 * freeze_fs. Subsequent calls to this without first thawing the fs will return
1030 int freeze_super(struct super_block *sb)
1034 atomic_inc(&sb->s_active);
1035 down_write(&sb->s_umount);
1037 deactivate_locked_super(sb);
1041 if (sb->s_flags & MS_RDONLY) {
1042 sb->s_frozen = SB_FREEZE_TRANS;
1044 up_write(&sb->s_umount);
1048 sb->s_frozen = SB_FREEZE_WRITE;
1051 sync_filesystem(sb);
1053 sb->s_frozen = SB_FREEZE_TRANS;
1056 sync_blockdev(sb->s_bdev);
1057 if (sb->s_op->freeze_fs) {
1058 ret = sb->s_op->freeze_fs(sb);
1061 "VFS:Filesystem freeze failed\n");
1062 sb->s_frozen = SB_UNFROZEN;
1063 deactivate_locked_super(sb);
1067 up_write(&sb->s_umount);
1070 EXPORT_SYMBOL(freeze_super);
1073 * thaw_super -- unlock filesystem
1074 * @sb: the super to thaw
1076 * Unlocks the filesystem and marks it writeable again after freeze_super().
1078 int thaw_super(struct super_block *sb)
1082 down_write(&sb->s_umount);
1083 if (sb->s_frozen == SB_UNFROZEN) {
1084 up_write(&sb->s_umount);
1088 if (sb->s_flags & MS_RDONLY)
1091 if (sb->s_op->unfreeze_fs) {
1092 error = sb->s_op->unfreeze_fs(sb);
1095 "VFS:Filesystem thaw failed\n");
1096 sb->s_frozen = SB_FREEZE_TRANS;
1097 up_write(&sb->s_umount);
1103 sb->s_frozen = SB_UNFROZEN;
1105 wake_up(&sb->s_wait_unfrozen);
1106 deactivate_locked_super(sb);
1110 EXPORT_SYMBOL(thaw_super);