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Linux/fs/super.c

  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 
 40 static LIST_HEAD(super_blocks);
 41 static DEFINE_SPINLOCK(sb_lock);
 42 
 43 static 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  */
 56 static 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 
113 static 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 
139 static 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 
150 static 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  */
163 static 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  */
184 static 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         s->s_maxbytes = MAX_NON_LFS;
248         s->s_op = &default_op;
249         s->s_time_gran = 1000000000;
250         s->cleancache_poolid = CLEANCACHE_NO_POOL;
251 
252         s->s_shrink.seeks = DEFAULT_SEEKS;
253         s->s_shrink.scan_objects = super_cache_scan;
254         s->s_shrink.count_objects = super_cache_count;
255         s->s_shrink.batch = 1024;
256         s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
257         return s;
258 
259 fail:
260         destroy_super(s);
261         return NULL;
262 }
263 
264 /* Superblock refcounting  */
265 
266 /*
267  * Drop a superblock's refcount.  The caller must hold sb_lock.
268  */
269 static void __put_super(struct super_block *sb)
270 {
271         if (!--sb->s_count) {
272                 list_del_init(&sb->s_list);
273                 destroy_super(sb);
274         }
275 }
276 
277 /**
278  *      put_super       -       drop a temporary reference to superblock
279  *      @sb: superblock in question
280  *
281  *      Drops a temporary reference, frees superblock if there's no
282  *      references left.
283  */
284 static void put_super(struct super_block *sb)
285 {
286         spin_lock(&sb_lock);
287         __put_super(sb);
288         spin_unlock(&sb_lock);
289 }
290 
291 
292 /**
293  *      deactivate_locked_super -       drop an active reference to superblock
294  *      @s: superblock to deactivate
295  *
296  *      Drops an active reference to superblock, converting it into a temporary
297  *      one if there is no other active references left.  In that case we
298  *      tell fs driver to shut it down and drop the temporary reference we
299  *      had just acquired.
300  *
301  *      Caller holds exclusive lock on superblock; that lock is released.
302  */
303 void deactivate_locked_super(struct super_block *s)
304 {
305         struct file_system_type *fs = s->s_type;
306         if (atomic_dec_and_test(&s->s_active)) {
307                 cleancache_invalidate_fs(s);
308                 unregister_shrinker(&s->s_shrink);
309                 fs->kill_sb(s);
310 
311                 /*
312                  * Since list_lru_destroy() may sleep, we cannot call it from
313                  * put_super(), where we hold the sb_lock. Therefore we destroy
314                  * the lru lists right now.
315                  */
316                 list_lru_destroy(&s->s_dentry_lru);
317                 list_lru_destroy(&s->s_inode_lru);
318 
319                 put_filesystem(fs);
320                 put_super(s);
321         } else {
322                 up_write(&s->s_umount);
323         }
324 }
325 
326 EXPORT_SYMBOL(deactivate_locked_super);
327 
328 /**
329  *      deactivate_super        -       drop an active reference to superblock
330  *      @s: superblock to deactivate
331  *
332  *      Variant of deactivate_locked_super(), except that superblock is *not*
333  *      locked by caller.  If we are going to drop the final active reference,
334  *      lock will be acquired prior to that.
335  */
336 void deactivate_super(struct super_block *s)
337 {
338         if (!atomic_add_unless(&s->s_active, -1, 1)) {
339                 down_write(&s->s_umount);
340                 deactivate_locked_super(s);
341         }
342 }
343 
344 EXPORT_SYMBOL(deactivate_super);
345 
346 /**
347  *      grab_super - acquire an active reference
348  *      @s: reference we are trying to make active
349  *
350  *      Tries to acquire an active reference.  grab_super() is used when we
351  *      had just found a superblock in super_blocks or fs_type->fs_supers
352  *      and want to turn it into a full-blown active reference.  grab_super()
353  *      is called with sb_lock held and drops it.  Returns 1 in case of
354  *      success, 0 if we had failed (superblock contents was already dead or
355  *      dying when grab_super() had been called).  Note that this is only
356  *      called for superblocks not in rundown mode (== ones still on ->fs_supers
357  *      of their type), so increment of ->s_count is OK here.
358  */
359 static int grab_super(struct super_block *s) __releases(sb_lock)
360 {
361         s->s_count++;
362         spin_unlock(&sb_lock);
363         down_write(&s->s_umount);
364         if ((s->s_flags & MS_BORN) && atomic_inc_not_zero(&s->s_active)) {
365                 put_super(s);
366                 return 1;
367         }
368         up_write(&s->s_umount);
369         put_super(s);
370         return 0;
371 }
372 
373 /*
374  *      trylock_super - try to grab ->s_umount shared
375  *      @sb: reference we are trying to grab
376  *
377  *      Try to prevent fs shutdown.  This is used in places where we
378  *      cannot take an active reference but we need to ensure that the
379  *      filesystem is not shut down while we are working on it. It returns
380  *      false if we cannot acquire s_umount or if we lose the race and
381  *      filesystem already got into shutdown, and returns true with the s_umount
382  *      lock held in read mode in case of success. On successful return,
383  *      the caller must drop the s_umount lock when done.
384  *
385  *      Note that unlike get_super() et.al. this one does *not* bump ->s_count.
386  *      The reason why it's safe is that we are OK with doing trylock instead
387  *      of down_read().  There's a couple of places that are OK with that, but
388  *      it's very much not a general-purpose interface.
389  */
390 bool trylock_super(struct super_block *sb)
391 {
392         if (down_read_trylock(&sb->s_umount)) {
393                 if (!hlist_unhashed(&sb->s_instances) &&
394                     sb->s_root && (sb->s_flags & MS_BORN))
395                         return true;
396                 up_read(&sb->s_umount);
397         }
398 
399         return false;
400 }
401 
402 /**
403  *      generic_shutdown_super  -       common helper for ->kill_sb()
404  *      @sb: superblock to kill
405  *
406  *      generic_shutdown_super() does all fs-independent work on superblock
407  *      shutdown.  Typical ->kill_sb() should pick all fs-specific objects
408  *      that need destruction out of superblock, call generic_shutdown_super()
409  *      and release aforementioned objects.  Note: dentries and inodes _are_
410  *      taken care of and do not need specific handling.
411  *
412  *      Upon calling this function, the filesystem may no longer alter or
413  *      rearrange the set of dentries belonging to this super_block, nor may it
414  *      change the attachments of dentries to inodes.
415  */
416 void generic_shutdown_super(struct super_block *sb)
417 {
418         const struct super_operations *sop = sb->s_op;
419 
420         if (sb->s_root) {
421                 shrink_dcache_for_umount(sb);
422                 sync_filesystem(sb);
423                 sb->s_flags &= ~MS_ACTIVE;
424 
425                 fsnotify_unmount_inodes(sb);
426                 cgroup_writeback_umount();
427 
428                 evict_inodes(sb);
429 
430                 if (sb->s_dio_done_wq) {
431                         destroy_workqueue(sb->s_dio_done_wq);
432                         sb->s_dio_done_wq = NULL;
433                 }
434 
435                 if (sop->put_super)
436                         sop->put_super(sb);
437 
438                 if (!list_empty(&sb->s_inodes)) {
439                         printk("VFS: Busy inodes after unmount of %s. "
440                            "Self-destruct in 5 seconds.  Have a nice day...\n",
441                            sb->s_id);
442                 }
443         }
444         spin_lock(&sb_lock);
445         /* should be initialized for __put_super_and_need_restart() */
446         hlist_del_init(&sb->s_instances);
447         spin_unlock(&sb_lock);
448         up_write(&sb->s_umount);
449 }
450 
451 EXPORT_SYMBOL(generic_shutdown_super);
452 
453 /**
454  *      sget_userns -   find or create a superblock
455  *      @type:  filesystem type superblock should belong to
456  *      @test:  comparison callback
457  *      @set:   setup callback
458  *      @flags: mount flags
459  *      @user_ns: User namespace for the super_block
460  *      @data:  argument to each of them
461  */
462 struct super_block *sget_userns(struct file_system_type *type,
463                         int (*test)(struct super_block *,void *),
464                         int (*set)(struct super_block *,void *),
465                         int flags, struct user_namespace *user_ns,
466                         void *data)
467 {
468         struct super_block *s = NULL;
469         struct super_block *old;
470         int err;
471 
472         if (!(flags & MS_KERNMOUNT) &&
473             !(type->fs_flags & FS_USERNS_MOUNT) &&
474             !capable(CAP_SYS_ADMIN))
475                 return ERR_PTR(-EPERM);
476 retry:
477         spin_lock(&sb_lock);
478         if (test) {
479                 hlist_for_each_entry(old, &type->fs_supers, s_instances) {
480                         if (!test(old, data))
481                                 continue;
482                         if (user_ns != old->s_user_ns) {
483                                 spin_unlock(&sb_lock);
484                                 if (s) {
485                                         up_write(&s->s_umount);
486                                         destroy_super(s);
487                                 }
488                                 return ERR_PTR(-EBUSY);
489                         }
490                         if (!grab_super(old))
491                                 goto retry;
492                         if (s) {
493                                 up_write(&s->s_umount);
494                                 destroy_super(s);
495                                 s = NULL;
496                         }
497                         return old;
498                 }
499         }
500         if (!s) {
501                 spin_unlock(&sb_lock);
502                 s = alloc_super(type, flags, user_ns);
503                 if (!s)
504                         return ERR_PTR(-ENOMEM);
505                 goto retry;
506         }
507                 
508         err = set(s, data);
509         if (err) {
510                 spin_unlock(&sb_lock);
511                 up_write(&s->s_umount);
512                 destroy_super(s);
513                 return ERR_PTR(err);
514         }
515         s->s_type = type;
516         strlcpy(s->s_id, type->name, sizeof(s->s_id));
517         list_add_tail(&s->s_list, &super_blocks);
518         hlist_add_head(&s->s_instances, &type->fs_supers);
519         spin_unlock(&sb_lock);
520         get_filesystem(type);
521         register_shrinker(&s->s_shrink);
522         return s;
523 }
524 
525 EXPORT_SYMBOL(sget_userns);
526 
527 /**
528  *      sget    -       find or create a superblock
529  *      @type:    filesystem type superblock should belong to
530  *      @test:    comparison callback
531  *      @set:     setup callback
532  *      @flags:   mount flags
533  *      @data:    argument to each of them
534  */
535 struct super_block *sget(struct file_system_type *type,
536                         int (*test)(struct super_block *,void *),
537                         int (*set)(struct super_block *,void *),
538                         int flags,
539                         void *data)
540 {
541         struct user_namespace *user_ns = current_user_ns();
542 
543         /* Ensure the requestor has permissions over the target filesystem */
544         if (!(flags & MS_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN))
545                 return ERR_PTR(-EPERM);
546 
547         return sget_userns(type, test, set, flags, user_ns, data);
548 }
549 
550 EXPORT_SYMBOL(sget);
551 
552 void drop_super(struct super_block *sb)
553 {
554         up_read(&sb->s_umount);
555         put_super(sb);
556 }
557 
558 EXPORT_SYMBOL(drop_super);
559 
560 void drop_super_exclusive(struct super_block *sb)
561 {
562         up_write(&sb->s_umount);
563         put_super(sb);
564 }
565 EXPORT_SYMBOL(drop_super_exclusive);
566 
567 /**
568  *      iterate_supers - call function for all active superblocks
569  *      @f: function to call
570  *      @arg: argument to pass to it
571  *
572  *      Scans the superblock list and calls given function, passing it
573  *      locked superblock and given argument.
574  */
575 void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
576 {
577         struct super_block *sb, *p = NULL;
578 
579         spin_lock(&sb_lock);
580         list_for_each_entry(sb, &super_blocks, s_list) {
581                 if (hlist_unhashed(&sb->s_instances))
582                         continue;
583                 sb->s_count++;
584                 spin_unlock(&sb_lock);
585 
586                 down_read(&sb->s_umount);
587                 if (sb->s_root && (sb->s_flags & MS_BORN))
588                         f(sb, arg);
589                 up_read(&sb->s_umount);
590 
591                 spin_lock(&sb_lock);
592                 if (p)
593                         __put_super(p);
594                 p = sb;
595         }
596         if (p)
597                 __put_super(p);
598         spin_unlock(&sb_lock);
599 }
600 
601 /**
602  *      iterate_supers_type - call function for superblocks of given type
603  *      @type: fs type
604  *      @f: function to call
605  *      @arg: argument to pass to it
606  *
607  *      Scans the superblock list and calls given function, passing it
608  *      locked superblock and given argument.
609  */
610 void iterate_supers_type(struct file_system_type *type,
611         void (*f)(struct super_block *, void *), void *arg)
612 {
613         struct super_block *sb, *p = NULL;
614 
615         spin_lock(&sb_lock);
616         hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
617                 sb->s_count++;
618                 spin_unlock(&sb_lock);
619 
620                 down_read(&sb->s_umount);
621                 if (sb->s_root && (sb->s_flags & MS_BORN))
622                         f(sb, arg);
623                 up_read(&sb->s_umount);
624 
625                 spin_lock(&sb_lock);
626                 if (p)
627                         __put_super(p);
628                 p = sb;
629         }
630         if (p)
631                 __put_super(p);
632         spin_unlock(&sb_lock);
633 }
634 
635 EXPORT_SYMBOL(iterate_supers_type);
636 
637 static struct super_block *__get_super(struct block_device *bdev, bool excl)
638 {
639         struct super_block *sb;
640 
641         if (!bdev)
642                 return NULL;
643 
644         spin_lock(&sb_lock);
645 rescan:
646         list_for_each_entry(sb, &super_blocks, s_list) {
647                 if (hlist_unhashed(&sb->s_instances))
648                         continue;
649                 if (sb->s_bdev == bdev) {
650                         sb->s_count++;
651                         spin_unlock(&sb_lock);
652                         if (!excl)
653                                 down_read(&sb->s_umount);
654                         else
655                                 down_write(&sb->s_umount);
656                         /* still alive? */
657                         if (sb->s_root && (sb->s_flags & MS_BORN))
658                                 return sb;
659                         if (!excl)
660                                 up_read(&sb->s_umount);
661                         else
662                                 up_write(&sb->s_umount);
663                         /* nope, got unmounted */
664                         spin_lock(&sb_lock);
665                         __put_super(sb);
666                         goto rescan;
667                 }
668         }
669         spin_unlock(&sb_lock);
670         return NULL;
671 }
672 
673 /**
674  *      get_super - get the superblock of a device
675  *      @bdev: device to get the superblock for
676  *
677  *      Scans the superblock list and finds the superblock of the file system
678  *      mounted on the device given. %NULL is returned if no match is found.
679  */
680 struct super_block *get_super(struct block_device *bdev)
681 {
682         return __get_super(bdev, false);
683 }
684 EXPORT_SYMBOL(get_super);
685 
686 static struct super_block *__get_super_thawed(struct block_device *bdev,
687                                               bool excl)
688 {
689         while (1) {
690                 struct super_block *s = __get_super(bdev, excl);
691                 if (!s || s->s_writers.frozen == SB_UNFROZEN)
692                         return s;
693                 if (!excl)
694                         up_read(&s->s_umount);
695                 else
696                         up_write(&s->s_umount);
697                 wait_event(s->s_writers.wait_unfrozen,
698                            s->s_writers.frozen == SB_UNFROZEN);
699                 put_super(s);
700         }
701 }
702 
703 /**
704  *      get_super_thawed - get thawed superblock of a device
705  *      @bdev: device to get the superblock for
706  *
707  *      Scans the superblock list and finds the superblock of the file system
708  *      mounted on the device. The superblock is returned once it is thawed
709  *      (or immediately if it was not frozen). %NULL is returned if no match
710  *      is found.
711  */
712 struct super_block *get_super_thawed(struct block_device *bdev)
713 {
714         return __get_super_thawed(bdev, false);
715 }
716 EXPORT_SYMBOL(get_super_thawed);
717 
718 /**
719  *      get_super_exclusive_thawed - get thawed superblock of a device
720  *      @bdev: device to get the superblock for
721  *
722  *      Scans the superblock list and finds the superblock of the file system
723  *      mounted on the device. The superblock is returned once it is thawed
724  *      (or immediately if it was not frozen) and s_umount semaphore is held
725  *      in exclusive mode. %NULL is returned if no match is found.
726  */
727 struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
728 {
729         return __get_super_thawed(bdev, true);
730 }
731 EXPORT_SYMBOL(get_super_exclusive_thawed);
732 
733 /**
734  * get_active_super - get an active reference to the superblock of a device
735  * @bdev: device to get the superblock for
736  *
737  * Scans the superblock list and finds the superblock of the file system
738  * mounted on the device given.  Returns the superblock with an active
739  * reference or %NULL if none was found.
740  */
741 struct super_block *get_active_super(struct block_device *bdev)
742 {
743         struct super_block *sb;
744 
745         if (!bdev)
746                 return NULL;
747 
748 restart:
749         spin_lock(&sb_lock);
750         list_for_each_entry(sb, &super_blocks, s_list) {
751                 if (hlist_unhashed(&sb->s_instances))
752                         continue;
753                 if (sb->s_bdev == bdev) {
754                         if (!grab_super(sb))
755                                 goto restart;
756                         up_write(&sb->s_umount);
757                         return sb;
758                 }
759         }
760         spin_unlock(&sb_lock);
761         return NULL;
762 }
763  
764 struct super_block *user_get_super(dev_t dev)
765 {
766         struct super_block *sb;
767 
768         spin_lock(&sb_lock);
769 rescan:
770         list_for_each_entry(sb, &super_blocks, s_list) {
771                 if (hlist_unhashed(&sb->s_instances))
772                         continue;
773                 if (sb->s_dev ==  dev) {
774                         sb->s_count++;
775                         spin_unlock(&sb_lock);
776                         down_read(&sb->s_umount);
777                         /* still alive? */
778                         if (sb->s_root && (sb->s_flags & MS_BORN))
779                                 return sb;
780                         up_read(&sb->s_umount);
781                         /* nope, got unmounted */
782                         spin_lock(&sb_lock);
783                         __put_super(sb);
784                         goto rescan;
785                 }
786         }
787         spin_unlock(&sb_lock);
788         return NULL;
789 }
790 
791 /**
792  *      do_remount_sb - asks filesystem to change mount options.
793  *      @sb:    superblock in question
794  *      @flags: numeric part of options
795  *      @data:  the rest of options
796  *      @force: whether or not to force the change
797  *
798  *      Alters the mount options of a mounted file system.
799  */
800 int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
801 {
802         int retval;
803         int remount_ro;
804 
805         if (sb->s_writers.frozen != SB_UNFROZEN)
806                 return -EBUSY;
807 
808 #ifdef CONFIG_BLOCK
809         if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
810                 return -EACCES;
811 #endif
812 
813         remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
814 
815         if (remount_ro) {
816                 if (!hlist_empty(&sb->s_pins)) {
817                         up_write(&sb->s_umount);
818                         group_pin_kill(&sb->s_pins);
819                         down_write(&sb->s_umount);
820                         if (!sb->s_root)
821                                 return 0;
822                         if (sb->s_writers.frozen != SB_UNFROZEN)
823                                 return -EBUSY;
824                         remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
825                 }
826         }
827         shrink_dcache_sb(sb);
828 
829         /* If we are remounting RDONLY and current sb is read/write,
830            make sure there are no rw files opened */
831         if (remount_ro) {
832                 if (force) {
833                         sb->s_readonly_remount = 1;
834                         smp_wmb();
835                 } else {
836                         retval = sb_prepare_remount_readonly(sb);
837                         if (retval)
838                                 return retval;
839                 }
840         }
841 
842         if (sb->s_op->remount_fs) {
843                 retval = sb->s_op->remount_fs(sb, &flags, data);
844                 if (retval) {
845                         if (!force)
846                                 goto cancel_readonly;
847                         /* If forced remount, go ahead despite any errors */
848                         WARN(1, "forced remount of a %s fs returned %i\n",
849                              sb->s_type->name, retval);
850                 }
851         }
852         sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
853         /* Needs to be ordered wrt mnt_is_readonly() */
854         smp_wmb();
855         sb->s_readonly_remount = 0;
856 
857         /*
858          * Some filesystems modify their metadata via some other path than the
859          * bdev buffer cache (eg. use a private mapping, or directories in
860          * pagecache, etc). Also file data modifications go via their own
861          * mappings. So If we try to mount readonly then copy the filesystem
862          * from bdev, we could get stale data, so invalidate it to give a best
863          * effort at coherency.
864          */
865         if (remount_ro && sb->s_bdev)
866                 invalidate_bdev(sb->s_bdev);
867         return 0;
868 
869 cancel_readonly:
870         sb->s_readonly_remount = 0;
871         return retval;
872 }
873 
874 static void do_emergency_remount(struct work_struct *work)
875 {
876         struct super_block *sb, *p = NULL;
877 
878         spin_lock(&sb_lock);
879         list_for_each_entry(sb, &super_blocks, s_list) {
880                 if (hlist_unhashed(&sb->s_instances))
881                         continue;
882                 sb->s_count++;
883                 spin_unlock(&sb_lock);
884                 down_write(&sb->s_umount);
885                 if (sb->s_root && sb->s_bdev && (sb->s_flags & MS_BORN) &&
886                     !(sb->s_flags & MS_RDONLY)) {
887                         /*
888                          * What lock protects sb->s_flags??
889                          */
890                         do_remount_sb(sb, MS_RDONLY, NULL, 1);
891                 }
892                 up_write(&sb->s_umount);
893                 spin_lock(&sb_lock);
894                 if (p)
895                         __put_super(p);
896                 p = sb;
897         }
898         if (p)
899                 __put_super(p);
900         spin_unlock(&sb_lock);
901         kfree(work);
902         printk("Emergency Remount complete\n");
903 }
904 
905 void emergency_remount(void)
906 {
907         struct work_struct *work;
908 
909         work = kmalloc(sizeof(*work), GFP_ATOMIC);
910         if (work) {
911                 INIT_WORK(work, do_emergency_remount);
912                 schedule_work(work);
913         }
914 }
915 
916 /*
917  * Unnamed block devices are dummy devices used by virtual
918  * filesystems which don't use real block-devices.  -- jrs
919  */
920 
921 static DEFINE_IDA(unnamed_dev_ida);
922 static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
923 /* Many userspace utilities consider an FSID of 0 invalid.
924  * Always return at least 1 from get_anon_bdev.
925  */
926 static int unnamed_dev_start = 1;
927 
928 int get_anon_bdev(dev_t *p)
929 {
930         int dev;
931         int error;
932 
933  retry:
934         if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
935                 return -ENOMEM;
936         spin_lock(&unnamed_dev_lock);
937         error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
938         if (!error)
939                 unnamed_dev_start = dev + 1;
940         spin_unlock(&unnamed_dev_lock);
941         if (error == -EAGAIN)
942                 /* We raced and lost with another CPU. */
943                 goto retry;
944         else if (error)
945                 return -EAGAIN;
946 
947         if (dev >= (1 << MINORBITS)) {
948                 spin_lock(&unnamed_dev_lock);
949                 ida_remove(&unnamed_dev_ida, dev);
950                 if (unnamed_dev_start > dev)
951                         unnamed_dev_start = dev;
952                 spin_unlock(&unnamed_dev_lock);
953                 return -EMFILE;
954         }
955         *p = MKDEV(0, dev & MINORMASK);
956         return 0;
957 }
958 EXPORT_SYMBOL(get_anon_bdev);
959 
960 void free_anon_bdev(dev_t dev)
961 {
962         int slot = MINOR(dev);
963         spin_lock(&unnamed_dev_lock);
964         ida_remove(&unnamed_dev_ida, slot);
965         if (slot < unnamed_dev_start)
966                 unnamed_dev_start = slot;
967         spin_unlock(&unnamed_dev_lock);
968 }
969 EXPORT_SYMBOL(free_anon_bdev);
970 
971 int set_anon_super(struct super_block *s, void *data)
972 {
973         return get_anon_bdev(&s->s_dev);
974 }
975 
976 EXPORT_SYMBOL(set_anon_super);
977 
978 void kill_anon_super(struct super_block *sb)
979 {
980         dev_t dev = sb->s_dev;
981         generic_shutdown_super(sb);
982         free_anon_bdev(dev);
983 }
984 
985 EXPORT_SYMBOL(kill_anon_super);
986 
987 void kill_litter_super(struct super_block *sb)
988 {
989         if (sb->s_root)
990                 d_genocide(sb->s_root);
991         kill_anon_super(sb);
992 }
993 
994 EXPORT_SYMBOL(kill_litter_super);
995 
996 static int ns_test_super(struct super_block *sb, void *data)
997 {
998         return sb->s_fs_info == data;
999 }
1000 
1001 static int ns_set_super(struct super_block *sb, void *data)
1002 {
1003         sb->s_fs_info = data;
1004         return set_anon_super(sb, NULL);
1005 }
1006 
1007 struct dentry *mount_ns(struct file_system_type *fs_type,
1008         int flags, void *data, void *ns, struct user_namespace *user_ns,
1009         int (*fill_super)(struct super_block *, void *, int))
1010 {
1011         struct super_block *sb;
1012 
1013         /* Don't allow mounting unless the caller has CAP_SYS_ADMIN
1014          * over the namespace.
1015          */
1016         if (!(flags & MS_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN))
1017                 return ERR_PTR(-EPERM);
1018 
1019         sb = sget_userns(fs_type, ns_test_super, ns_set_super, flags,
1020                          user_ns, ns);
1021         if (IS_ERR(sb))
1022                 return ERR_CAST(sb);
1023 
1024         if (!sb->s_root) {
1025                 int err;
1026                 err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
1027                 if (err) {
1028                         deactivate_locked_super(sb);
1029                         return ERR_PTR(err);
1030                 }
1031 
1032                 sb->s_flags |= MS_ACTIVE;
1033         }
1034 
1035         return dget(sb->s_root);
1036 }
1037 
1038 EXPORT_SYMBOL(mount_ns);
1039 
1040 #ifdef CONFIG_BLOCK
1041 static int set_bdev_super(struct super_block *s, void *data)
1042 {
1043         s->s_bdev = data;
1044         s->s_dev = s->s_bdev->bd_dev;
1045 
1046         /*
1047          * We set the bdi here to the queue backing, file systems can
1048          * overwrite this in ->fill_super()
1049          */
1050         s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
1051         return 0;
1052 }
1053 
1054 static int test_bdev_super(struct super_block *s, void *data)
1055 {
1056         return (void *)s->s_bdev == data;
1057 }
1058 
1059 struct dentry *mount_bdev(struct file_system_type *fs_type,
1060         int flags, const char *dev_name, void *data,
1061         int (*fill_super)(struct super_block *, void *, int))
1062 {
1063         struct block_device *bdev;
1064         struct super_block *s;
1065         fmode_t mode = FMODE_READ | FMODE_EXCL;
1066         int error = 0;
1067 
1068         if (!(flags & MS_RDONLY))
1069                 mode |= FMODE_WRITE;
1070 
1071         bdev = blkdev_get_by_path(dev_name, mode, fs_type);
1072         if (IS_ERR(bdev))
1073                 return ERR_CAST(bdev);
1074 
1075         /*
1076          * once the super is inserted into the list by sget, s_umount
1077          * will protect the lockfs code from trying to start a snapshot
1078          * while we are mounting
1079          */
1080         mutex_lock(&bdev->bd_fsfreeze_mutex);
1081         if (bdev->bd_fsfreeze_count > 0) {
1082                 mutex_unlock(&bdev->bd_fsfreeze_mutex);
1083                 error = -EBUSY;
1084                 goto error_bdev;
1085         }
1086         s = sget(fs_type, test_bdev_super, set_bdev_super, flags | MS_NOSEC,
1087                  bdev);
1088         mutex_unlock(&bdev->bd_fsfreeze_mutex);
1089         if (IS_ERR(s))
1090                 goto error_s;
1091 
1092         if (s->s_root) {
1093                 if ((flags ^ s->s_flags) & MS_RDONLY) {
1094                         deactivate_locked_super(s);
1095                         error = -EBUSY;
1096                         goto error_bdev;
1097                 }
1098 
1099                 /*
1100                  * s_umount nests inside bd_mutex during
1101                  * __invalidate_device().  blkdev_put() acquires
1102                  * bd_mutex and can't be called under s_umount.  Drop
1103                  * s_umount temporarily.  This is safe as we're
1104                  * holding an active reference.
1105                  */
1106                 up_write(&s->s_umount);
1107                 blkdev_put(bdev, mode);
1108                 down_write(&s->s_umount);
1109         } else {
1110                 s->s_mode = mode;
1111                 snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1112                 sb_set_blocksize(s, block_size(bdev));
1113                 error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1114                 if (error) {
1115                         deactivate_locked_super(s);
1116                         goto error;
1117                 }
1118 
1119                 s->s_flags |= MS_ACTIVE;
1120                 bdev->bd_super = s;
1121         }
1122 
1123         return dget(s->s_root);
1124 
1125 error_s:
1126         error = PTR_ERR(s);
1127 error_bdev:
1128         blkdev_put(bdev, mode);
1129 error:
1130         return ERR_PTR(error);
1131 }
1132 EXPORT_SYMBOL(mount_bdev);
1133 
1134 void kill_block_super(struct super_block *sb)
1135 {
1136         struct block_device *bdev = sb->s_bdev;
1137         fmode_t mode = sb->s_mode;
1138 
1139         bdev->bd_super = NULL;
1140         generic_shutdown_super(sb);
1141         sync_blockdev(bdev);
1142         WARN_ON_ONCE(!(mode & FMODE_EXCL));
1143         blkdev_put(bdev, mode | FMODE_EXCL);
1144 }
1145 
1146 EXPORT_SYMBOL(kill_block_super);
1147 #endif
1148 
1149 struct dentry *mount_nodev(struct file_system_type *fs_type,
1150         int flags, void *data,
1151         int (*fill_super)(struct super_block *, void *, int))
1152 {
1153         int error;
1154         struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1155 
1156         if (IS_ERR(s))
1157                 return ERR_CAST(s);
1158 
1159         error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1160         if (error) {
1161                 deactivate_locked_super(s);
1162                 return ERR_PTR(error);
1163         }
1164         s->s_flags |= MS_ACTIVE;
1165         return dget(s->s_root);
1166 }
1167 EXPORT_SYMBOL(mount_nodev);
1168 
1169 static int compare_single(struct super_block *s, void *p)
1170 {
1171         return 1;
1172 }
1173 
1174 struct dentry *mount_single(struct file_system_type *fs_type,
1175         int flags, void *data,
1176         int (*fill_super)(struct super_block *, void *, int))
1177 {
1178         struct super_block *s;
1179         int error;
1180 
1181         s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1182         if (IS_ERR(s))
1183                 return ERR_CAST(s);
1184         if (!s->s_root) {
1185                 error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1186                 if (error) {
1187                         deactivate_locked_super(s);
1188                         return ERR_PTR(error);
1189                 }
1190                 s->s_flags |= MS_ACTIVE;
1191         } else {
1192                 do_remount_sb(s, flags, data, 0);
1193         }
1194         return dget(s->s_root);
1195 }
1196 EXPORT_SYMBOL(mount_single);
1197 
1198 struct dentry *
1199 mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
1200 {
1201         struct dentry *root;
1202         struct super_block *sb;
1203         char *secdata = NULL;
1204         int error = -ENOMEM;
1205 
1206         if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
1207                 secdata = alloc_secdata();
1208                 if (!secdata)
1209                         goto out;
1210 
1211                 error = security_sb_copy_data(data, secdata);
1212                 if (error)
1213                         goto out_free_secdata;
1214         }
1215 
1216         root = type->mount(type, flags, name, data);
1217         if (IS_ERR(root)) {
1218                 error = PTR_ERR(root);
1219                 goto out_free_secdata;
1220         }
1221         sb = root->d_sb;
1222         BUG_ON(!sb);
1223         WARN_ON(!sb->s_bdi);
1224         sb->s_flags |= MS_BORN;
1225 
1226         error = security_sb_kern_mount(sb, flags, secdata);
1227         if (error)
1228                 goto out_sb;
1229 
1230         /*
1231          * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1232          * but s_maxbytes was an unsigned long long for many releases. Throw
1233          * this warning for a little while to try and catch filesystems that
1234          * violate this rule.
1235          */
1236         WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1237                 "negative value (%lld)\n", type->name, sb->s_maxbytes);
1238 
1239         up_write(&sb->s_umount);
1240         free_secdata(secdata);
1241         return root;
1242 out_sb:
1243         dput(root);
1244         deactivate_locked_super(sb);
1245 out_free_secdata:
1246         free_secdata(secdata);
1247 out:
1248         return ERR_PTR(error);
1249 }
1250 
1251 /*
1252  * This is an internal function, please use sb_end_{write,pagefault,intwrite}
1253  * instead.
1254  */
1255 void __sb_end_write(struct super_block *sb, int level)
1256 {
1257         percpu_up_read(sb->s_writers.rw_sem + level-1);
1258 }
1259 EXPORT_SYMBOL(__sb_end_write);
1260 
1261 /*
1262  * This is an internal function, please use sb_start_{write,pagefault,intwrite}
1263  * instead.
1264  */
1265 int __sb_start_write(struct super_block *sb, int level, bool wait)
1266 {
1267         bool force_trylock = false;
1268         int ret = 1;
1269 
1270 #ifdef CONFIG_LOCKDEP
1271         /*
1272          * We want lockdep to tell us about possible deadlocks with freezing
1273          * but it's it bit tricky to properly instrument it. Getting a freeze
1274          * protection works as getting a read lock but there are subtle
1275          * problems. XFS for example gets freeze protection on internal level
1276          * twice in some cases, which is OK only because we already hold a
1277          * freeze protection also on higher level. Due to these cases we have
1278          * to use wait == F (trylock mode) which must not fail.
1279          */
1280         if (wait) {
1281                 int i;
1282 
1283                 for (i = 0; i < level - 1; i++)
1284                         if (percpu_rwsem_is_held(sb->s_writers.rw_sem + i)) {
1285                                 force_trylock = true;
1286                                 break;
1287                         }
1288         }
1289 #endif
1290         if (wait && !force_trylock)
1291                 percpu_down_read(sb->s_writers.rw_sem + level-1);
1292         else
1293                 ret = percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
1294 
1295         WARN_ON(force_trylock && !ret);
1296         return ret;
1297 }
1298 EXPORT_SYMBOL(__sb_start_write);
1299 
1300 /**
1301  * sb_wait_write - wait until all writers to given file system finish
1302  * @sb: the super for which we wait
1303  * @level: type of writers we wait for (normal vs page fault)
1304  *
1305  * This function waits until there are no writers of given type to given file
1306  * system.
1307  */
1308 static void sb_wait_write(struct super_block *sb, int level)
1309 {
1310         percpu_down_write(sb->s_writers.rw_sem + level-1);
1311 }
1312 
1313 /*
1314  * We are going to return to userspace and forget about these locks, the
1315  * ownership goes to the caller of thaw_super() which does unlock().
1316  */
1317 static void lockdep_sb_freeze_release(struct super_block *sb)
1318 {
1319         int level;
1320 
1321         for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1322                 percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1323 }
1324 
1325 /*
1326  * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
1327  */
1328 static void lockdep_sb_freeze_acquire(struct super_block *sb)
1329 {
1330         int level;
1331 
1332         for (level = 0; level < SB_FREEZE_LEVELS; ++level)
1333                 percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1334 }
1335 
1336 static void sb_freeze_unlock(struct super_block *sb)
1337 {
1338         int level;
1339 
1340         for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1341                 percpu_up_write(sb->s_writers.rw_sem + level);
1342 }
1343 
1344 /**
1345  * freeze_super - lock the filesystem and force it into a consistent state
1346  * @sb: the super to lock
1347  *
1348  * Syncs the super to make sure the filesystem is consistent and calls the fs's
1349  * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1350  * -EBUSY.
1351  *
1352  * During this function, sb->s_writers.frozen goes through these values:
1353  *
1354  * SB_UNFROZEN: File system is normal, all writes progress as usual.
1355  *
1356  * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
1357  * writes should be blocked, though page faults are still allowed. We wait for
1358  * all writes to complete and then proceed to the next stage.
1359  *
1360  * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1361  * but internal fs threads can still modify the filesystem (although they
1362  * should not dirty new pages or inodes), writeback can run etc. After waiting
1363  * for all running page faults we sync the filesystem which will clean all
1364  * dirty pages and inodes (no new dirty pages or inodes can be created when
1365  * sync is running).
1366  *
1367  * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1368  * modification are blocked (e.g. XFS preallocation truncation on inode
1369  * reclaim). This is usually implemented by blocking new transactions for
1370  * filesystems that have them and need this additional guard. After all
1371  * internal writers are finished we call ->freeze_fs() to finish filesystem
1372  * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1373  * mostly auxiliary for filesystems to verify they do not modify frozen fs.
1374  *
1375  * sb->s_writers.frozen is protected by sb->s_umount.
1376  */
1377 int freeze_super(struct super_block *sb)
1378 {
1379         int ret;
1380 
1381         atomic_inc(&sb->s_active);
1382         down_write(&sb->s_umount);
1383         if (sb->s_writers.frozen != SB_UNFROZEN) {
1384                 deactivate_locked_super(sb);
1385                 return -EBUSY;
1386         }
1387 
1388         if (!(sb->s_flags & MS_BORN)) {
1389                 up_write(&sb->s_umount);
1390                 return 0;       /* sic - it's "nothing to do" */
1391         }
1392 
1393         if (sb->s_flags & MS_RDONLY) {
1394                 /* Nothing to do really... */
1395                 sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1396                 up_write(&sb->s_umount);
1397                 return 0;
1398         }
1399 
1400         sb->s_writers.frozen = SB_FREEZE_WRITE;
1401         /* Release s_umount to preserve sb_start_write -> s_umount ordering */
1402         up_write(&sb->s_umount);
1403         sb_wait_write(sb, SB_FREEZE_WRITE);
1404         down_write(&sb->s_umount);
1405 
1406         /* Now we go and block page faults... */
1407         sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1408         sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1409 
1410         /* All writers are done so after syncing there won't be dirty data */
1411         sync_filesystem(sb);
1412 
1413         /* Now wait for internal filesystem counter */
1414         sb->s_writers.frozen = SB_FREEZE_FS;
1415         sb_wait_write(sb, SB_FREEZE_FS);
1416 
1417         if (sb->s_op->freeze_fs) {
1418                 ret = sb->s_op->freeze_fs(sb);
1419                 if (ret) {
1420                         printk(KERN_ERR
1421                                 "VFS:Filesystem freeze failed\n");
1422                         sb->s_writers.frozen = SB_UNFROZEN;
1423                         sb_freeze_unlock(sb);
1424                         wake_up(&sb->s_writers.wait_unfrozen);
1425                         deactivate_locked_super(sb);
1426                         return ret;
1427                 }
1428         }
1429         /*
1430          * For debugging purposes so that fs can warn if it sees write activity
1431          * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
1432          */
1433         sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1434         lockdep_sb_freeze_release(sb);
1435         up_write(&sb->s_umount);
1436         return 0;
1437 }
1438 EXPORT_SYMBOL(freeze_super);
1439 
1440 /**
1441  * thaw_super -- unlock filesystem
1442  * @sb: the super to thaw
1443  *
1444  * Unlocks the filesystem and marks it writeable again after freeze_super().
1445  */
1446 int thaw_super(struct super_block *sb)
1447 {
1448         int error;
1449 
1450         down_write(&sb->s_umount);
1451         if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
1452                 up_write(&sb->s_umount);
1453                 return -EINVAL;
1454         }
1455 
1456         if (sb->s_flags & MS_RDONLY) {
1457                 sb->s_writers.frozen = SB_UNFROZEN;
1458                 goto out;
1459         }
1460 
1461         lockdep_sb_freeze_acquire(sb);
1462 
1463         if (sb->s_op->unfreeze_fs) {
1464                 error = sb->s_op->unfreeze_fs(sb);
1465                 if (error) {
1466                         printk(KERN_ERR
1467                                 "VFS:Filesystem thaw failed\n");
1468                         lockdep_sb_freeze_release(sb);
1469                         up_write(&sb->s_umount);
1470                         return error;
1471                 }
1472         }
1473 
1474         sb->s_writers.frozen = SB_UNFROZEN;
1475         sb_freeze_unlock(sb);
1476 out:
1477         wake_up(&sb->s_writers.wait_unfrozen);
1478         deactivate_locked_super(sb);
1479         return 0;
1480 }
1481 EXPORT_SYMBOL(thaw_super);
1482 

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