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TOMOYO Linux Cross Reference
Linux/fs/super.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *  linux/fs/super.c
  4  *
  5  *  Copyright (C) 1991, 1992  Linus Torvalds
  6  *
  7  *  super.c contains code to handle: - mount structures
  8  *                                   - super-block tables
  9  *                                   - filesystem drivers list
 10  *                                   - mount system call
 11  *                                   - umount system call
 12  *                                   - ustat system call
 13  *
 14  * GK 2/5/95  -  Changed to support mounting the root fs via NFS
 15  *
 16  *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
 17  *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
 18  *  Added options to /proc/mounts:
 19  *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
 20  *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
 21  *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
 22  */
 23 
 24 #include <linux/export.h>
 25 #include <linux/slab.h>
 26 #include <linux/blkdev.h>
 27 #include <linux/mount.h>
 28 #include <linux/security.h>
 29 #include <linux/writeback.h>            /* for the emergency remount stuff */
 30 #include <linux/idr.h>
 31 #include <linux/mutex.h>
 32 #include <linux/backing-dev.h>
 33 #include <linux/rculist_bl.h>
 34 #include <linux/cleancache.h>
 35 #include <linux/fsnotify.h>
 36 #include <linux/lockdep.h>
 37 #include <linux/user_namespace.h>
 38 #include "internal.h"
 39 
 40 static int thaw_super_locked(struct super_block *sb);
 41 
 42 static LIST_HEAD(super_blocks);
 43 static DEFINE_SPINLOCK(sb_lock);
 44 
 45 static char *sb_writers_name[SB_FREEZE_LEVELS] = {
 46         "sb_writers",
 47         "sb_pagefaults",
 48         "sb_internal",
 49 };
 50 
 51 /*
 52  * One thing we have to be careful of with a per-sb shrinker is that we don't
 53  * drop the last active reference to the superblock from within the shrinker.
 54  * If that happens we could trigger unregistering the shrinker from within the
 55  * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
 56  * take a passive reference to the superblock to avoid this from occurring.
 57  */
 58 static unsigned long super_cache_scan(struct shrinker *shrink,
 59                                       struct shrink_control *sc)
 60 {
 61         struct super_block *sb;
 62         long    fs_objects = 0;
 63         long    total_objects;
 64         long    freed = 0;
 65         long    dentries;
 66         long    inodes;
 67 
 68         sb = container_of(shrink, struct super_block, s_shrink);
 69 
 70         /*
 71          * Deadlock avoidance.  We may hold various FS locks, and we don't want
 72          * to recurse into the FS that called us in clear_inode() and friends..
 73          */
 74         if (!(sc->gfp_mask & __GFP_FS))
 75                 return SHRINK_STOP;
 76 
 77         if (!trylock_super(sb))
 78                 return SHRINK_STOP;
 79 
 80         if (sb->s_op->nr_cached_objects)
 81                 fs_objects = sb->s_op->nr_cached_objects(sb, sc);
 82 
 83         inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
 84         dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc);
 85         total_objects = dentries + inodes + fs_objects + 1;
 86         if (!total_objects)
 87                 total_objects = 1;
 88 
 89         /* proportion the scan between the caches */
 90         dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);
 91         inodes = mult_frac(sc->nr_to_scan, inodes, total_objects);
 92         fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
 93 
 94         /*
 95          * prune the dcache first as the icache is pinned by it, then
 96          * prune the icache, followed by the filesystem specific caches
 97          *
 98          * Ensure that we always scan at least one object - memcg kmem
 99          * accounting uses this to fully empty the caches.
100          */
101         sc->nr_to_scan = dentries + 1;
102         freed = prune_dcache_sb(sb, sc);
103         sc->nr_to_scan = inodes + 1;
104         freed += prune_icache_sb(sb, sc);
105 
106         if (fs_objects) {
107                 sc->nr_to_scan = fs_objects + 1;
108                 freed += sb->s_op->free_cached_objects(sb, sc);
109         }
110 
111         up_read(&sb->s_umount);
112         return freed;
113 }
114 
115 static unsigned long super_cache_count(struct shrinker *shrink,
116                                        struct shrink_control *sc)
117 {
118         struct super_block *sb;
119         long    total_objects = 0;
120 
121         sb = container_of(shrink, struct super_block, s_shrink);
122 
123         /*
124          * We don't call trylock_super() here as it is a scalability bottleneck,
125          * so we're exposed to partial setup state. The shrinker rwsem does not
126          * protect filesystem operations backing list_lru_shrink_count() or
127          * s_op->nr_cached_objects(). Counts can change between
128          * super_cache_count and super_cache_scan, so we really don't need locks
129          * here.
130          *
131          * However, if we are currently mounting the superblock, the underlying
132          * filesystem might be in a state of partial construction and hence it
133          * is dangerous to access it.  trylock_super() uses a SB_BORN check to
134          * avoid this situation, so do the same here. The memory barrier is
135          * matched with the one in mount_fs() as we don't hold locks here.
136          */
137         if (!(sb->s_flags & SB_BORN))
138                 return 0;
139         smp_rmb();
140 
141         if (sb->s_op && sb->s_op->nr_cached_objects)
142                 total_objects = sb->s_op->nr_cached_objects(sb, sc);
143 
144         total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
145         total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
146 
147         total_objects = vfs_pressure_ratio(total_objects);
148         return total_objects;
149 }
150 
151 static void destroy_super_work(struct work_struct *work)
152 {
153         struct super_block *s = container_of(work, struct super_block,
154                                                         destroy_work);
155         int i;
156 
157         for (i = 0; i < SB_FREEZE_LEVELS; i++)
158                 percpu_free_rwsem(&s->s_writers.rw_sem[i]);
159         kfree(s);
160 }
161 
162 static void destroy_super_rcu(struct rcu_head *head)
163 {
164         struct super_block *s = container_of(head, struct super_block, rcu);
165         INIT_WORK(&s->destroy_work, destroy_super_work);
166         schedule_work(&s->destroy_work);
167 }
168 
169 /* Free a superblock that has never been seen by anyone */
170 static void destroy_unused_super(struct super_block *s)
171 {
172         if (!s)
173                 return;
174         up_write(&s->s_umount);
175         list_lru_destroy(&s->s_dentry_lru);
176         list_lru_destroy(&s->s_inode_lru);
177         security_sb_free(s);
178         put_user_ns(s->s_user_ns);
179         kfree(s->s_subtype);
180         free_prealloced_shrinker(&s->s_shrink);
181         /* no delays needed */
182         destroy_super_work(&s->destroy_work);
183 }
184 
185 /**
186  *      alloc_super     -       create new superblock
187  *      @type:  filesystem type superblock should belong to
188  *      @flags: the mount flags
189  *      @user_ns: User namespace for the super_block
190  *
191  *      Allocates and initializes a new &struct super_block.  alloc_super()
192  *      returns a pointer new superblock or %NULL if allocation had failed.
193  */
194 static struct super_block *alloc_super(struct file_system_type *type, int flags,
195                                        struct user_namespace *user_ns)
196 {
197         struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
198         static const struct super_operations default_op;
199         int i;
200 
201         if (!s)
202                 return NULL;
203 
204         INIT_LIST_HEAD(&s->s_mounts);
205         s->s_user_ns = get_user_ns(user_ns);
206         init_rwsem(&s->s_umount);
207         lockdep_set_class(&s->s_umount, &type->s_umount_key);
208         /*
209          * sget() can have s_umount recursion.
210          *
211          * When it cannot find a suitable sb, it allocates a new
212          * one (this one), and tries again to find a suitable old
213          * one.
214          *
215          * In case that succeeds, it will acquire the s_umount
216          * lock of the old one. Since these are clearly distrinct
217          * locks, and this object isn't exposed yet, there's no
218          * risk of deadlocks.
219          *
220          * Annotate this by putting this lock in a different
221          * subclass.
222          */
223         down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
224 
225         if (security_sb_alloc(s))
226                 goto fail;
227 
228         for (i = 0; i < SB_FREEZE_LEVELS; i++) {
229                 if (__percpu_init_rwsem(&s->s_writers.rw_sem[i],
230                                         sb_writers_name[i],
231                                         &type->s_writers_key[i]))
232                         goto fail;
233         }
234         init_waitqueue_head(&s->s_writers.wait_unfrozen);
235         s->s_bdi = &noop_backing_dev_info;
236         s->s_flags = flags;
237         if (s->s_user_ns != &init_user_ns)
238                 s->s_iflags |= SB_I_NODEV;
239         INIT_HLIST_NODE(&s->s_instances);
240         INIT_HLIST_BL_HEAD(&s->s_roots);
241         mutex_init(&s->s_sync_lock);
242         INIT_LIST_HEAD(&s->s_inodes);
243         spin_lock_init(&s->s_inode_list_lock);
244         INIT_LIST_HEAD(&s->s_inodes_wb);
245         spin_lock_init(&s->s_inode_wblist_lock);
246 
247         if (list_lru_init_memcg(&s->s_dentry_lru))
248                 goto fail;
249         if (list_lru_init_memcg(&s->s_inode_lru))
250                 goto fail;
251         s->s_count = 1;
252         atomic_set(&s->s_active, 1);
253         mutex_init(&s->s_vfs_rename_mutex);
254         lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
255         init_rwsem(&s->s_dquot.dqio_sem);
256         s->s_maxbytes = MAX_NON_LFS;
257         s->s_op = &default_op;
258         s->s_time_gran = 1000000000;
259         s->cleancache_poolid = CLEANCACHE_NO_POOL;
260 
261         s->s_shrink.seeks = DEFAULT_SEEKS;
262         s->s_shrink.scan_objects = super_cache_scan;
263         s->s_shrink.count_objects = super_cache_count;
264         s->s_shrink.batch = 1024;
265         s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
266         if (prealloc_shrinker(&s->s_shrink))
267                 goto fail;
268         return s;
269 
270 fail:
271         destroy_unused_super(s);
272         return NULL;
273 }
274 
275 /* Superblock refcounting  */
276 
277 /*
278  * Drop a superblock's refcount.  The caller must hold sb_lock.
279  */
280 static void __put_super(struct super_block *s)
281 {
282         if (!--s->s_count) {
283                 list_del_init(&s->s_list);
284                 WARN_ON(s->s_dentry_lru.node);
285                 WARN_ON(s->s_inode_lru.node);
286                 WARN_ON(!list_empty(&s->s_mounts));
287                 security_sb_free(s);
288                 put_user_ns(s->s_user_ns);
289                 kfree(s->s_subtype);
290                 call_rcu(&s->rcu, destroy_super_rcu);
291         }
292 }
293 
294 /**
295  *      put_super       -       drop a temporary reference to superblock
296  *      @sb: superblock in question
297  *
298  *      Drops a temporary reference, frees superblock if there's no
299  *      references left.
300  */
301 static void put_super(struct super_block *sb)
302 {
303         spin_lock(&sb_lock);
304         __put_super(sb);
305         spin_unlock(&sb_lock);
306 }
307 
308 
309 /**
310  *      deactivate_locked_super -       drop an active reference to superblock
311  *      @s: superblock to deactivate
312  *
313  *      Drops an active reference to superblock, converting it into a temporary
314  *      one if there is no other active references left.  In that case we
315  *      tell fs driver to shut it down and drop the temporary reference we
316  *      had just acquired.
317  *
318  *      Caller holds exclusive lock on superblock; that lock is released.
319  */
320 void deactivate_locked_super(struct super_block *s)
321 {
322         struct file_system_type *fs = s->s_type;
323         if (atomic_dec_and_test(&s->s_active)) {
324                 cleancache_invalidate_fs(s);
325                 unregister_shrinker(&s->s_shrink);
326                 fs->kill_sb(s);
327 
328                 /*
329                  * Since list_lru_destroy() may sleep, we cannot call it from
330                  * put_super(), where we hold the sb_lock. Therefore we destroy
331                  * the lru lists right now.
332                  */
333                 list_lru_destroy(&s->s_dentry_lru);
334                 list_lru_destroy(&s->s_inode_lru);
335 
336                 put_filesystem(fs);
337                 put_super(s);
338         } else {
339                 up_write(&s->s_umount);
340         }
341 }
342 
343 EXPORT_SYMBOL(deactivate_locked_super);
344 
345 /**
346  *      deactivate_super        -       drop an active reference to superblock
347  *      @s: superblock to deactivate
348  *
349  *      Variant of deactivate_locked_super(), except that superblock is *not*
350  *      locked by caller.  If we are going to drop the final active reference,
351  *      lock will be acquired prior to that.
352  */
353 void deactivate_super(struct super_block *s)
354 {
355         if (!atomic_add_unless(&s->s_active, -1, 1)) {
356                 down_write(&s->s_umount);
357                 deactivate_locked_super(s);
358         }
359 }
360 
361 EXPORT_SYMBOL(deactivate_super);
362 
363 /**
364  *      grab_super - acquire an active reference
365  *      @s: reference we are trying to make active
366  *
367  *      Tries to acquire an active reference.  grab_super() is used when we
368  *      had just found a superblock in super_blocks or fs_type->fs_supers
369  *      and want to turn it into a full-blown active reference.  grab_super()
370  *      is called with sb_lock held and drops it.  Returns 1 in case of
371  *      success, 0 if we had failed (superblock contents was already dead or
372  *      dying when grab_super() had been called).  Note that this is only
373  *      called for superblocks not in rundown mode (== ones still on ->fs_supers
374  *      of their type), so increment of ->s_count is OK here.
375  */
376 static int grab_super(struct super_block *s) __releases(sb_lock)
377 {
378         s->s_count++;
379         spin_unlock(&sb_lock);
380         down_write(&s->s_umount);
381         if ((s->s_flags & SB_BORN) && atomic_inc_not_zero(&s->s_active)) {
382                 put_super(s);
383                 return 1;
384         }
385         up_write(&s->s_umount);
386         put_super(s);
387         return 0;
388 }
389 
390 /*
391  *      trylock_super - try to grab ->s_umount shared
392  *      @sb: reference we are trying to grab
393  *
394  *      Try to prevent fs shutdown.  This is used in places where we
395  *      cannot take an active reference but we need to ensure that the
396  *      filesystem is not shut down while we are working on it. It returns
397  *      false if we cannot acquire s_umount or if we lose the race and
398  *      filesystem already got into shutdown, and returns true with the s_umount
399  *      lock held in read mode in case of success. On successful return,
400  *      the caller must drop the s_umount lock when done.
401  *
402  *      Note that unlike get_super() et.al. this one does *not* bump ->s_count.
403  *      The reason why it's safe is that we are OK with doing trylock instead
404  *      of down_read().  There's a couple of places that are OK with that, but
405  *      it's very much not a general-purpose interface.
406  */
407 bool trylock_super(struct super_block *sb)
408 {
409         if (down_read_trylock(&sb->s_umount)) {
410                 if (!hlist_unhashed(&sb->s_instances) &&
411                     sb->s_root && (sb->s_flags & SB_BORN))
412                         return true;
413                 up_read(&sb->s_umount);
414         }
415 
416         return false;
417 }
418 
419 /**
420  *      generic_shutdown_super  -       common helper for ->kill_sb()
421  *      @sb: superblock to kill
422  *
423  *      generic_shutdown_super() does all fs-independent work on superblock
424  *      shutdown.  Typical ->kill_sb() should pick all fs-specific objects
425  *      that need destruction out of superblock, call generic_shutdown_super()
426  *      and release aforementioned objects.  Note: dentries and inodes _are_
427  *      taken care of and do not need specific handling.
428  *
429  *      Upon calling this function, the filesystem may no longer alter or
430  *      rearrange the set of dentries belonging to this super_block, nor may it
431  *      change the attachments of dentries to inodes.
432  */
433 void generic_shutdown_super(struct super_block *sb)
434 {
435         const struct super_operations *sop = sb->s_op;
436 
437         if (sb->s_root) {
438                 shrink_dcache_for_umount(sb);
439                 sync_filesystem(sb);
440                 sb->s_flags &= ~SB_ACTIVE;
441 
442                 fsnotify_unmount_inodes(sb);
443                 cgroup_writeback_umount();
444 
445                 evict_inodes(sb);
446 
447                 if (sb->s_dio_done_wq) {
448                         destroy_workqueue(sb->s_dio_done_wq);
449                         sb->s_dio_done_wq = NULL;
450                 }
451 
452                 if (sop->put_super)
453                         sop->put_super(sb);
454 
455                 if (!list_empty(&sb->s_inodes)) {
456                         printk("VFS: Busy inodes after unmount of %s. "
457                            "Self-destruct in 5 seconds.  Have a nice day...\n",
458                            sb->s_id);
459                 }
460         }
461         spin_lock(&sb_lock);
462         /* should be initialized for __put_super_and_need_restart() */
463         hlist_del_init(&sb->s_instances);
464         spin_unlock(&sb_lock);
465         up_write(&sb->s_umount);
466         if (sb->s_bdi != &noop_backing_dev_info) {
467                 bdi_put(sb->s_bdi);
468                 sb->s_bdi = &noop_backing_dev_info;
469         }
470 }
471 
472 EXPORT_SYMBOL(generic_shutdown_super);
473 
474 /**
475  *      sget_userns -   find or create a superblock
476  *      @type:  filesystem type superblock should belong to
477  *      @test:  comparison callback
478  *      @set:   setup callback
479  *      @flags: mount flags
480  *      @user_ns: User namespace for the super_block
481  *      @data:  argument to each of them
482  */
483 struct super_block *sget_userns(struct file_system_type *type,
484                         int (*test)(struct super_block *,void *),
485                         int (*set)(struct super_block *,void *),
486                         int flags, struct user_namespace *user_ns,
487                         void *data)
488 {
489         struct super_block *s = NULL;
490         struct super_block *old;
491         int err;
492 
493         if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) &&
494             !(type->fs_flags & FS_USERNS_MOUNT) &&
495             !capable(CAP_SYS_ADMIN))
496                 return ERR_PTR(-EPERM);
497 retry:
498         spin_lock(&sb_lock);
499         if (test) {
500                 hlist_for_each_entry(old, &type->fs_supers, s_instances) {
501                         if (!test(old, data))
502                                 continue;
503                         if (user_ns != old->s_user_ns) {
504                                 spin_unlock(&sb_lock);
505                                 destroy_unused_super(s);
506                                 return ERR_PTR(-EBUSY);
507                         }
508                         if (!grab_super(old))
509                                 goto retry;
510                         destroy_unused_super(s);
511                         return old;
512                 }
513         }
514         if (!s) {
515                 spin_unlock(&sb_lock);
516                 s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
517                 if (!s)
518                         return ERR_PTR(-ENOMEM);
519                 goto retry;
520         }
521 
522         err = set(s, data);
523         if (err) {
524                 spin_unlock(&sb_lock);
525                 destroy_unused_super(s);
526                 return ERR_PTR(err);
527         }
528         s->s_type = type;
529         strlcpy(s->s_id, type->name, sizeof(s->s_id));
530         list_add_tail(&s->s_list, &super_blocks);
531         hlist_add_head(&s->s_instances, &type->fs_supers);
532         spin_unlock(&sb_lock);
533         get_filesystem(type);
534         register_shrinker_prepared(&s->s_shrink);
535         return s;
536 }
537 
538 EXPORT_SYMBOL(sget_userns);
539 
540 /**
541  *      sget    -       find or create a superblock
542  *      @type:    filesystem type superblock should belong to
543  *      @test:    comparison callback
544  *      @set:     setup callback
545  *      @flags:   mount flags
546  *      @data:    argument to each of them
547  */
548 struct super_block *sget(struct file_system_type *type,
549                         int (*test)(struct super_block *,void *),
550                         int (*set)(struct super_block *,void *),
551                         int flags,
552                         void *data)
553 {
554         struct user_namespace *user_ns = current_user_ns();
555 
556         /* We don't yet pass the user namespace of the parent
557          * mount through to here so always use &init_user_ns
558          * until that changes.
559          */
560         if (flags & SB_SUBMOUNT)
561                 user_ns = &init_user_ns;
562 
563         /* Ensure the requestor has permissions over the target filesystem */
564         if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) && !ns_capable(user_ns, CAP_SYS_ADMIN))
565                 return ERR_PTR(-EPERM);
566 
567         return sget_userns(type, test, set, flags, user_ns, data);
568 }
569 
570 EXPORT_SYMBOL(sget);
571 
572 void drop_super(struct super_block *sb)
573 {
574         up_read(&sb->s_umount);
575         put_super(sb);
576 }
577 
578 EXPORT_SYMBOL(drop_super);
579 
580 void drop_super_exclusive(struct super_block *sb)
581 {
582         up_write(&sb->s_umount);
583         put_super(sb);
584 }
585 EXPORT_SYMBOL(drop_super_exclusive);
586 
587 static void __iterate_supers(void (*f)(struct super_block *))
588 {
589         struct super_block *sb, *p = NULL;
590 
591         spin_lock(&sb_lock);
592         list_for_each_entry(sb, &super_blocks, s_list) {
593                 if (hlist_unhashed(&sb->s_instances))
594                         continue;
595                 sb->s_count++;
596                 spin_unlock(&sb_lock);
597 
598                 f(sb);
599 
600                 spin_lock(&sb_lock);
601                 if (p)
602                         __put_super(p);
603                 p = sb;
604         }
605         if (p)
606                 __put_super(p);
607         spin_unlock(&sb_lock);
608 }
609 /**
610  *      iterate_supers - call function for all active superblocks
611  *      @f: function to call
612  *      @arg: argument to pass to it
613  *
614  *      Scans the superblock list and calls given function, passing it
615  *      locked superblock and given argument.
616  */
617 void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
618 {
619         struct super_block *sb, *p = NULL;
620 
621         spin_lock(&sb_lock);
622         list_for_each_entry(sb, &super_blocks, s_list) {
623                 if (hlist_unhashed(&sb->s_instances))
624                         continue;
625                 sb->s_count++;
626                 spin_unlock(&sb_lock);
627 
628                 down_read(&sb->s_umount);
629                 if (sb->s_root && (sb->s_flags & SB_BORN))
630                         f(sb, arg);
631                 up_read(&sb->s_umount);
632 
633                 spin_lock(&sb_lock);
634                 if (p)
635                         __put_super(p);
636                 p = sb;
637         }
638         if (p)
639                 __put_super(p);
640         spin_unlock(&sb_lock);
641 }
642 
643 /**
644  *      iterate_supers_type - call function for superblocks of given type
645  *      @type: fs type
646  *      @f: function to call
647  *      @arg: argument to pass to it
648  *
649  *      Scans the superblock list and calls given function, passing it
650  *      locked superblock and given argument.
651  */
652 void iterate_supers_type(struct file_system_type *type,
653         void (*f)(struct super_block *, void *), void *arg)
654 {
655         struct super_block *sb, *p = NULL;
656 
657         spin_lock(&sb_lock);
658         hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
659                 sb->s_count++;
660                 spin_unlock(&sb_lock);
661 
662                 down_read(&sb->s_umount);
663                 if (sb->s_root && (sb->s_flags & SB_BORN))
664                         f(sb, arg);
665                 up_read(&sb->s_umount);
666 
667                 spin_lock(&sb_lock);
668                 if (p)
669                         __put_super(p);
670                 p = sb;
671         }
672         if (p)
673                 __put_super(p);
674         spin_unlock(&sb_lock);
675 }
676 
677 EXPORT_SYMBOL(iterate_supers_type);
678 
679 static struct super_block *__get_super(struct block_device *bdev, bool excl)
680 {
681         struct super_block *sb;
682 
683         if (!bdev)
684                 return NULL;
685 
686         spin_lock(&sb_lock);
687 rescan:
688         list_for_each_entry(sb, &super_blocks, s_list) {
689                 if (hlist_unhashed(&sb->s_instances))
690                         continue;
691                 if (sb->s_bdev == bdev) {
692                         sb->s_count++;
693                         spin_unlock(&sb_lock);
694                         if (!excl)
695                                 down_read(&sb->s_umount);
696                         else
697                                 down_write(&sb->s_umount);
698                         /* still alive? */
699                         if (sb->s_root && (sb->s_flags & SB_BORN))
700                                 return sb;
701                         if (!excl)
702                                 up_read(&sb->s_umount);
703                         else
704                                 up_write(&sb->s_umount);
705                         /* nope, got unmounted */
706                         spin_lock(&sb_lock);
707                         __put_super(sb);
708                         goto rescan;
709                 }
710         }
711         spin_unlock(&sb_lock);
712         return NULL;
713 }
714 
715 /**
716  *      get_super - get the superblock of a device
717  *      @bdev: device to get the superblock for
718  *
719  *      Scans the superblock list and finds the superblock of the file system
720  *      mounted on the device given. %NULL is returned if no match is found.
721  */
722 struct super_block *get_super(struct block_device *bdev)
723 {
724         return __get_super(bdev, false);
725 }
726 EXPORT_SYMBOL(get_super);
727 
728 static struct super_block *__get_super_thawed(struct block_device *bdev,
729                                               bool excl)
730 {
731         while (1) {
732                 struct super_block *s = __get_super(bdev, excl);
733                 if (!s || s->s_writers.frozen == SB_UNFROZEN)
734                         return s;
735                 if (!excl)
736                         up_read(&s->s_umount);
737                 else
738                         up_write(&s->s_umount);
739                 wait_event(s->s_writers.wait_unfrozen,
740                            s->s_writers.frozen == SB_UNFROZEN);
741                 put_super(s);
742         }
743 }
744 
745 /**
746  *      get_super_thawed - get thawed superblock of a device
747  *      @bdev: device to get the superblock for
748  *
749  *      Scans the superblock list and finds the superblock of the file system
750  *      mounted on the device. The superblock is returned once it is thawed
751  *      (or immediately if it was not frozen). %NULL is returned if no match
752  *      is found.
753  */
754 struct super_block *get_super_thawed(struct block_device *bdev)
755 {
756         return __get_super_thawed(bdev, false);
757 }
758 EXPORT_SYMBOL(get_super_thawed);
759 
760 /**
761  *      get_super_exclusive_thawed - get thawed superblock of a device
762  *      @bdev: device to get the superblock for
763  *
764  *      Scans the superblock list and finds the superblock of the file system
765  *      mounted on the device. The superblock is returned once it is thawed
766  *      (or immediately if it was not frozen) and s_umount semaphore is held
767  *      in exclusive mode. %NULL is returned if no match is found.
768  */
769 struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
770 {
771         return __get_super_thawed(bdev, true);
772 }
773 EXPORT_SYMBOL(get_super_exclusive_thawed);
774 
775 /**
776  * get_active_super - get an active reference to the superblock of a device
777  * @bdev: device to get the superblock for
778  *
779  * Scans the superblock list and finds the superblock of the file system
780  * mounted on the device given.  Returns the superblock with an active
781  * reference or %NULL if none was found.
782  */
783 struct super_block *get_active_super(struct block_device *bdev)
784 {
785         struct super_block *sb;
786 
787         if (!bdev)
788                 return NULL;
789 
790 restart:
791         spin_lock(&sb_lock);
792         list_for_each_entry(sb, &super_blocks, s_list) {
793                 if (hlist_unhashed(&sb->s_instances))
794                         continue;
795                 if (sb->s_bdev == bdev) {
796                         if (!grab_super(sb))
797                                 goto restart;
798                         up_write(&sb->s_umount);
799                         return sb;
800                 }
801         }
802         spin_unlock(&sb_lock);
803         return NULL;
804 }
805 
806 struct super_block *user_get_super(dev_t dev)
807 {
808         struct super_block *sb;
809 
810         spin_lock(&sb_lock);
811 rescan:
812         list_for_each_entry(sb, &super_blocks, s_list) {
813                 if (hlist_unhashed(&sb->s_instances))
814                         continue;
815                 if (sb->s_dev ==  dev) {
816                         sb->s_count++;
817                         spin_unlock(&sb_lock);
818                         down_read(&sb->s_umount);
819                         /* still alive? */
820                         if (sb->s_root && (sb->s_flags & SB_BORN))
821                                 return sb;
822                         up_read(&sb->s_umount);
823                         /* nope, got unmounted */
824                         spin_lock(&sb_lock);
825                         __put_super(sb);
826                         goto rescan;
827                 }
828         }
829         spin_unlock(&sb_lock);
830         return NULL;
831 }
832 
833 /**
834  *      do_remount_sb - asks filesystem to change mount options.
835  *      @sb:    superblock in question
836  *      @sb_flags: revised superblock flags
837  *      @data:  the rest of options
838  *      @force: whether or not to force the change
839  *
840  *      Alters the mount options of a mounted file system.
841  */
842 int do_remount_sb(struct super_block *sb, int sb_flags, void *data, int force)
843 {
844         int retval;
845         int remount_ro;
846 
847         if (sb->s_writers.frozen != SB_UNFROZEN)
848                 return -EBUSY;
849 
850 #ifdef CONFIG_BLOCK
851         if (!(sb_flags & SB_RDONLY) && bdev_read_only(sb->s_bdev))
852                 return -EACCES;
853 #endif
854 
855         remount_ro = (sb_flags & SB_RDONLY) && !sb_rdonly(sb);
856 
857         if (remount_ro) {
858                 if (!hlist_empty(&sb->s_pins)) {
859                         up_write(&sb->s_umount);
860                         group_pin_kill(&sb->s_pins);
861                         down_write(&sb->s_umount);
862                         if (!sb->s_root)
863                                 return 0;
864                         if (sb->s_writers.frozen != SB_UNFROZEN)
865                                 return -EBUSY;
866                         remount_ro = (sb_flags & SB_RDONLY) && !sb_rdonly(sb);
867                 }
868         }
869         shrink_dcache_sb(sb);
870 
871         /* If we are remounting RDONLY and current sb is read/write,
872            make sure there are no rw files opened */
873         if (remount_ro) {
874                 if (force) {
875                         sb->s_readonly_remount = 1;
876                         smp_wmb();
877                 } else {
878                         retval = sb_prepare_remount_readonly(sb);
879                         if (retval)
880                                 return retval;
881                 }
882         }
883 
884         if (sb->s_op->remount_fs) {
885                 retval = sb->s_op->remount_fs(sb, &sb_flags, data);
886                 if (retval) {
887                         if (!force)
888                                 goto cancel_readonly;
889                         /* If forced remount, go ahead despite any errors */
890                         WARN(1, "forced remount of a %s fs returned %i\n",
891                              sb->s_type->name, retval);
892                 }
893         }
894         sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (sb_flags & MS_RMT_MASK);
895         /* Needs to be ordered wrt mnt_is_readonly() */
896         smp_wmb();
897         sb->s_readonly_remount = 0;
898 
899         /*
900          * Some filesystems modify their metadata via some other path than the
901          * bdev buffer cache (eg. use a private mapping, or directories in
902          * pagecache, etc). Also file data modifications go via their own
903          * mappings. So If we try to mount readonly then copy the filesystem
904          * from bdev, we could get stale data, so invalidate it to give a best
905          * effort at coherency.
906          */
907         if (remount_ro && sb->s_bdev)
908                 invalidate_bdev(sb->s_bdev);
909         return 0;
910 
911 cancel_readonly:
912         sb->s_readonly_remount = 0;
913         return retval;
914 }
915 
916 static void do_emergency_remount_callback(struct super_block *sb)
917 {
918         down_write(&sb->s_umount);
919         if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
920             !sb_rdonly(sb)) {
921                 /*
922                  * What lock protects sb->s_flags??
923                  */
924                 do_remount_sb(sb, SB_RDONLY, NULL, 1);
925         }
926         up_write(&sb->s_umount);
927 }
928 
929 static void do_emergency_remount(struct work_struct *work)
930 {
931         __iterate_supers(do_emergency_remount_callback);
932         kfree(work);
933         printk("Emergency Remount complete\n");
934 }
935 
936 void emergency_remount(void)
937 {
938         struct work_struct *work;
939 
940         work = kmalloc(sizeof(*work), GFP_ATOMIC);
941         if (work) {
942                 INIT_WORK(work, do_emergency_remount);
943                 schedule_work(work);
944         }
945 }
946 
947 static void do_thaw_all_callback(struct super_block *sb)
948 {
949         down_write(&sb->s_umount);
950         if (sb->s_root && sb->s_flags & MS_BORN) {
951                 emergency_thaw_bdev(sb);
952                 thaw_super_locked(sb);
953         } else {
954                 up_write(&sb->s_umount);
955         }
956 }
957 
958 static void do_thaw_all(struct work_struct *work)
959 {
960         __iterate_supers(do_thaw_all_callback);
961         kfree(work);
962         printk(KERN_WARNING "Emergency Thaw complete\n");
963 }
964 
965 /**
966  * emergency_thaw_all -- forcibly thaw every frozen filesystem
967  *
968  * Used for emergency unfreeze of all filesystems via SysRq
969  */
970 void emergency_thaw_all(void)
971 {
972         struct work_struct *work;
973 
974         work = kmalloc(sizeof(*work), GFP_ATOMIC);
975         if (work) {
976                 INIT_WORK(work, do_thaw_all);
977                 schedule_work(work);
978         }
979 }
980 
981 /*
982  * Unnamed block devices are dummy devices used by virtual
983  * filesystems which don't use real block-devices.  -- jrs
984  */
985 
986 static DEFINE_IDA(unnamed_dev_ida);
987 static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
988 /* Many userspace utilities consider an FSID of 0 invalid.
989  * Always return at least 1 from get_anon_bdev.
990  */
991 static int unnamed_dev_start = 1;
992 
993 int get_anon_bdev(dev_t *p)
994 {
995         int dev;
996         int error;
997 
998  retry:
999         if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
1000                 return -ENOMEM;
1001         spin_lock(&unnamed_dev_lock);
1002         error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
1003         if (!error)
1004                 unnamed_dev_start = dev + 1;
1005         spin_unlock(&unnamed_dev_lock);
1006         if (error == -EAGAIN)
1007                 /* We raced and lost with another CPU. */
1008                 goto retry;
1009         else if (error)
1010                 return -EAGAIN;
1011 
1012         if (dev >= (1 << MINORBITS)) {
1013                 spin_lock(&unnamed_dev_lock);
1014                 ida_remove(&unnamed_dev_ida, dev);
1015                 if (unnamed_dev_start > dev)
1016                         unnamed_dev_start = dev;
1017                 spin_unlock(&unnamed_dev_lock);
1018                 return -EMFILE;
1019         }
1020         *p = MKDEV(0, dev & MINORMASK);
1021         return 0;
1022 }
1023 EXPORT_SYMBOL(get_anon_bdev);
1024 
1025 void free_anon_bdev(dev_t dev)
1026 {
1027         int slot = MINOR(dev);
1028         spin_lock(&unnamed_dev_lock);
1029         ida_remove(&unnamed_dev_ida, slot);
1030         if (slot < unnamed_dev_start)
1031                 unnamed_dev_start = slot;
1032         spin_unlock(&unnamed_dev_lock);
1033 }
1034 EXPORT_SYMBOL(free_anon_bdev);
1035 
1036 int set_anon_super(struct super_block *s, void *data)
1037 {
1038         return get_anon_bdev(&s->s_dev);
1039 }
1040 
1041 EXPORT_SYMBOL(set_anon_super);
1042 
1043 void kill_anon_super(struct super_block *sb)
1044 {
1045         dev_t dev = sb->s_dev;
1046         generic_shutdown_super(sb);
1047         free_anon_bdev(dev);
1048 }
1049 
1050 EXPORT_SYMBOL(kill_anon_super);
1051 
1052 void kill_litter_super(struct super_block *sb)
1053 {
1054         if (sb->s_root)
1055                 d_genocide(sb->s_root);
1056         kill_anon_super(sb);
1057 }
1058 
1059 EXPORT_SYMBOL(kill_litter_super);
1060 
1061 static int ns_test_super(struct super_block *sb, void *data)
1062 {
1063         return sb->s_fs_info == data;
1064 }
1065 
1066 static int ns_set_super(struct super_block *sb, void *data)
1067 {
1068         sb->s_fs_info = data;
1069         return set_anon_super(sb, NULL);
1070 }
1071 
1072 struct dentry *mount_ns(struct file_system_type *fs_type,
1073         int flags, void *data, void *ns, struct user_namespace *user_ns,
1074         int (*fill_super)(struct super_block *, void *, int))
1075 {
1076         struct super_block *sb;
1077 
1078         /* Don't allow mounting unless the caller has CAP_SYS_ADMIN
1079          * over the namespace.
1080          */
1081         if (!(flags & SB_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN))
1082                 return ERR_PTR(-EPERM);
1083 
1084         sb = sget_userns(fs_type, ns_test_super, ns_set_super, flags,
1085                          user_ns, ns);
1086         if (IS_ERR(sb))
1087                 return ERR_CAST(sb);
1088 
1089         if (!sb->s_root) {
1090                 int err;
1091                 err = fill_super(sb, data, flags & SB_SILENT ? 1 : 0);
1092                 if (err) {
1093                         deactivate_locked_super(sb);
1094                         return ERR_PTR(err);
1095                 }
1096 
1097                 sb->s_flags |= SB_ACTIVE;
1098         }
1099 
1100         return dget(sb->s_root);
1101 }
1102 
1103 EXPORT_SYMBOL(mount_ns);
1104 
1105 #ifdef CONFIG_BLOCK
1106 static int set_bdev_super(struct super_block *s, void *data)
1107 {
1108         s->s_bdev = data;
1109         s->s_dev = s->s_bdev->bd_dev;
1110         s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
1111 
1112         return 0;
1113 }
1114 
1115 static int test_bdev_super(struct super_block *s, void *data)
1116 {
1117         return (void *)s->s_bdev == data;
1118 }
1119 
1120 struct dentry *mount_bdev(struct file_system_type *fs_type,
1121         int flags, const char *dev_name, void *data,
1122         int (*fill_super)(struct super_block *, void *, int))
1123 {
1124         struct block_device *bdev;
1125         struct super_block *s;
1126         fmode_t mode = FMODE_READ | FMODE_EXCL;
1127         int error = 0;
1128 
1129         if (!(flags & SB_RDONLY))
1130                 mode |= FMODE_WRITE;
1131 
1132         bdev = blkdev_get_by_path(dev_name, mode, fs_type);
1133         if (IS_ERR(bdev))
1134                 return ERR_CAST(bdev);
1135 
1136         /*
1137          * once the super is inserted into the list by sget, s_umount
1138          * will protect the lockfs code from trying to start a snapshot
1139          * while we are mounting
1140          */
1141         mutex_lock(&bdev->bd_fsfreeze_mutex);
1142         if (bdev->bd_fsfreeze_count > 0) {
1143                 mutex_unlock(&bdev->bd_fsfreeze_mutex);
1144                 error = -EBUSY;
1145                 goto error_bdev;
1146         }
1147         s = sget(fs_type, test_bdev_super, set_bdev_super, flags | SB_NOSEC,
1148                  bdev);
1149         mutex_unlock(&bdev->bd_fsfreeze_mutex);
1150         if (IS_ERR(s))
1151                 goto error_s;
1152 
1153         if (s->s_root) {
1154                 if ((flags ^ s->s_flags) & SB_RDONLY) {
1155                         deactivate_locked_super(s);
1156                         error = -EBUSY;
1157                         goto error_bdev;
1158                 }
1159 
1160                 /*
1161                  * s_umount nests inside bd_mutex during
1162                  * __invalidate_device().  blkdev_put() acquires
1163                  * bd_mutex and can't be called under s_umount.  Drop
1164                  * s_umount temporarily.  This is safe as we're
1165                  * holding an active reference.
1166                  */
1167                 up_write(&s->s_umount);
1168                 blkdev_put(bdev, mode);
1169                 down_write(&s->s_umount);
1170         } else {
1171                 s->s_mode = mode;
1172                 snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1173                 sb_set_blocksize(s, block_size(bdev));
1174                 error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1175                 if (error) {
1176                         deactivate_locked_super(s);
1177                         goto error;
1178                 }
1179 
1180                 s->s_flags |= SB_ACTIVE;
1181                 bdev->bd_super = s;
1182         }
1183 
1184         return dget(s->s_root);
1185 
1186 error_s:
1187         error = PTR_ERR(s);
1188 error_bdev:
1189         blkdev_put(bdev, mode);
1190 error:
1191         return ERR_PTR(error);
1192 }
1193 EXPORT_SYMBOL(mount_bdev);
1194 
1195 void kill_block_super(struct super_block *sb)
1196 {
1197         struct block_device *bdev = sb->s_bdev;
1198         fmode_t mode = sb->s_mode;
1199 
1200         bdev->bd_super = NULL;
1201         generic_shutdown_super(sb);
1202         sync_blockdev(bdev);
1203         WARN_ON_ONCE(!(mode & FMODE_EXCL));
1204         blkdev_put(bdev, mode | FMODE_EXCL);
1205 }
1206 
1207 EXPORT_SYMBOL(kill_block_super);
1208 #endif
1209 
1210 struct dentry *mount_nodev(struct file_system_type *fs_type,
1211         int flags, void *data,
1212         int (*fill_super)(struct super_block *, void *, int))
1213 {
1214         int error;
1215         struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1216 
1217         if (IS_ERR(s))
1218                 return ERR_CAST(s);
1219 
1220         error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1221         if (error) {
1222                 deactivate_locked_super(s);
1223                 return ERR_PTR(error);
1224         }
1225         s->s_flags |= SB_ACTIVE;
1226         return dget(s->s_root);
1227 }
1228 EXPORT_SYMBOL(mount_nodev);
1229 
1230 static int compare_single(struct super_block *s, void *p)
1231 {
1232         return 1;
1233 }
1234 
1235 struct dentry *mount_single(struct file_system_type *fs_type,
1236         int flags, void *data,
1237         int (*fill_super)(struct super_block *, void *, int))
1238 {
1239         struct super_block *s;
1240         int error;
1241 
1242         s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1243         if (IS_ERR(s))
1244                 return ERR_CAST(s);
1245         if (!s->s_root) {
1246                 error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1247                 if (error) {
1248                         deactivate_locked_super(s);
1249                         return ERR_PTR(error);
1250                 }
1251                 s->s_flags |= SB_ACTIVE;
1252         } else {
1253                 do_remount_sb(s, flags, data, 0);
1254         }
1255         return dget(s->s_root);
1256 }
1257 EXPORT_SYMBOL(mount_single);
1258 
1259 struct dentry *
1260 mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
1261 {
1262         struct dentry *root;
1263         struct super_block *sb;
1264         char *secdata = NULL;
1265         int error = -ENOMEM;
1266 
1267         if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
1268                 secdata = alloc_secdata();
1269                 if (!secdata)
1270                         goto out;
1271 
1272                 error = security_sb_copy_data(data, secdata);
1273                 if (error)
1274                         goto out_free_secdata;
1275         }
1276 
1277         root = type->mount(type, flags, name, data);
1278         if (IS_ERR(root)) {
1279                 error = PTR_ERR(root);
1280                 goto out_free_secdata;
1281         }
1282         sb = root->d_sb;
1283         BUG_ON(!sb);
1284         WARN_ON(!sb->s_bdi);
1285 
1286         /*
1287          * Write barrier is for super_cache_count(). We place it before setting
1288          * SB_BORN as the data dependency between the two functions is the
1289          * superblock structure contents that we just set up, not the SB_BORN
1290          * flag.
1291          */
1292         smp_wmb();
1293         sb->s_flags |= SB_BORN;
1294 
1295         error = security_sb_kern_mount(sb, flags, secdata);
1296         if (error)
1297                 goto out_sb;
1298 
1299         /*
1300          * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1301          * but s_maxbytes was an unsigned long long for many releases. Throw
1302          * this warning for a little while to try and catch filesystems that
1303          * violate this rule.
1304          */
1305         WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1306                 "negative value (%lld)\n", type->name, sb->s_maxbytes);
1307 
1308         up_write(&sb->s_umount);
1309         free_secdata(secdata);
1310         return root;
1311 out_sb:
1312         dput(root);
1313         deactivate_locked_super(sb);
1314 out_free_secdata:
1315         free_secdata(secdata);
1316 out:
1317         return ERR_PTR(error);
1318 }
1319 
1320 /*
1321  * Setup private BDI for given superblock. It gets automatically cleaned up
1322  * in generic_shutdown_super().
1323  */
1324 int super_setup_bdi_name(struct super_block *sb, char *fmt, ...)
1325 {
1326         struct backing_dev_info *bdi;
1327         int err;
1328         va_list args;
1329 
1330         bdi = bdi_alloc(GFP_KERNEL);
1331         if (!bdi)
1332                 return -ENOMEM;
1333 
1334         bdi->name = sb->s_type->name;
1335 
1336         va_start(args, fmt);
1337         err = bdi_register_va(bdi, fmt, args);
1338         va_end(args);
1339         if (err) {
1340                 bdi_put(bdi);
1341                 return err;
1342         }
1343         WARN_ON(sb->s_bdi != &noop_backing_dev_info);
1344         sb->s_bdi = bdi;
1345 
1346         return 0;
1347 }
1348 EXPORT_SYMBOL(super_setup_bdi_name);
1349 
1350 /*
1351  * Setup private BDI for given superblock. I gets automatically cleaned up
1352  * in generic_shutdown_super().
1353  */
1354 int super_setup_bdi(struct super_block *sb)
1355 {
1356         static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
1357 
1358         return super_setup_bdi_name(sb, "%.28s-%ld", sb->s_type->name,
1359                                     atomic_long_inc_return(&bdi_seq));
1360 }
1361 EXPORT_SYMBOL(super_setup_bdi);
1362 
1363 /*
1364  * This is an internal function, please use sb_end_{write,pagefault,intwrite}
1365  * instead.
1366  */
1367 void __sb_end_write(struct super_block *sb, int level)
1368 {
1369         percpu_up_read(sb->s_writers.rw_sem + level-1);
1370 }
1371 EXPORT_SYMBOL(__sb_end_write);
1372 
1373 /*
1374  * This is an internal function, please use sb_start_{write,pagefault,intwrite}
1375  * instead.
1376  */
1377 int __sb_start_write(struct super_block *sb, int level, bool wait)
1378 {
1379         bool force_trylock = false;
1380         int ret = 1;
1381 
1382 #ifdef CONFIG_LOCKDEP
1383         /*
1384          * We want lockdep to tell us about possible deadlocks with freezing
1385          * but it's it bit tricky to properly instrument it. Getting a freeze
1386          * protection works as getting a read lock but there are subtle
1387          * problems. XFS for example gets freeze protection on internal level
1388          * twice in some cases, which is OK only because we already hold a
1389          * freeze protection also on higher level. Due to these cases we have
1390          * to use wait == F (trylock mode) which must not fail.
1391          */
1392         if (wait) {
1393                 int i;
1394 
1395                 for (i = 0; i < level - 1; i++)
1396                         if (percpu_rwsem_is_held(sb->s_writers.rw_sem + i)) {
1397                                 force_trylock = true;
1398                                 break;
1399                         }
1400         }
1401 #endif
1402         if (wait && !force_trylock)
1403                 percpu_down_read(sb->s_writers.rw_sem + level-1);
1404         else
1405                 ret = percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
1406 
1407         WARN_ON(force_trylock && !ret);
1408         return ret;
1409 }
1410 EXPORT_SYMBOL(__sb_start_write);
1411 
1412 /**
1413  * sb_wait_write - wait until all writers to given file system finish
1414  * @sb: the super for which we wait
1415  * @level: type of writers we wait for (normal vs page fault)
1416  *
1417  * This function waits until there are no writers of given type to given file
1418  * system.
1419  */
1420 static void sb_wait_write(struct super_block *sb, int level)
1421 {
1422         percpu_down_write(sb->s_writers.rw_sem + level-1);
1423 }
1424 
1425 /*
1426  * We are going to return to userspace and forget about these locks, the
1427  * ownership goes to the caller of thaw_super() which does unlock().
1428  */
1429 static void lockdep_sb_freeze_release(struct super_block *sb)
1430 {
1431         int level;
1432 
1433         for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1434                 percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1435 }
1436 
1437 /*
1438  * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
1439  */
1440 static void lockdep_sb_freeze_acquire(struct super_block *sb)
1441 {
1442         int level;
1443 
1444         for (level = 0; level < SB_FREEZE_LEVELS; ++level)
1445                 percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1446 }
1447 
1448 static void sb_freeze_unlock(struct super_block *sb)
1449 {
1450         int level;
1451 
1452         for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1453                 percpu_up_write(sb->s_writers.rw_sem + level);
1454 }
1455 
1456 /**
1457  * freeze_super - lock the filesystem and force it into a consistent state
1458  * @sb: the super to lock
1459  *
1460  * Syncs the super to make sure the filesystem is consistent and calls the fs's
1461  * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1462  * -EBUSY.
1463  *
1464  * During this function, sb->s_writers.frozen goes through these values:
1465  *
1466  * SB_UNFROZEN: File system is normal, all writes progress as usual.
1467  *
1468  * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
1469  * writes should be blocked, though page faults are still allowed. We wait for
1470  * all writes to complete and then proceed to the next stage.
1471  *
1472  * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1473  * but internal fs threads can still modify the filesystem (although they
1474  * should not dirty new pages or inodes), writeback can run etc. After waiting
1475  * for all running page faults we sync the filesystem which will clean all
1476  * dirty pages and inodes (no new dirty pages or inodes can be created when
1477  * sync is running).
1478  *
1479  * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1480  * modification are blocked (e.g. XFS preallocation truncation on inode
1481  * reclaim). This is usually implemented by blocking new transactions for
1482  * filesystems that have them and need this additional guard. After all
1483  * internal writers are finished we call ->freeze_fs() to finish filesystem
1484  * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1485  * mostly auxiliary for filesystems to verify they do not modify frozen fs.
1486  *
1487  * sb->s_writers.frozen is protected by sb->s_umount.
1488  */
1489 int freeze_super(struct super_block *sb)
1490 {
1491         int ret;
1492 
1493         atomic_inc(&sb->s_active);
1494         down_write(&sb->s_umount);
1495         if (sb->s_writers.frozen != SB_UNFROZEN) {
1496                 deactivate_locked_super(sb);
1497                 return -EBUSY;
1498         }
1499 
1500         if (!(sb->s_flags & SB_BORN)) {
1501                 up_write(&sb->s_umount);
1502                 return 0;       /* sic - it's "nothing to do" */
1503         }
1504 
1505         if (sb_rdonly(sb)) {
1506                 /* Nothing to do really... */
1507                 sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1508                 up_write(&sb->s_umount);
1509                 return 0;
1510         }
1511 
1512         sb->s_writers.frozen = SB_FREEZE_WRITE;
1513         /* Release s_umount to preserve sb_start_write -> s_umount ordering */
1514         up_write(&sb->s_umount);
1515         sb_wait_write(sb, SB_FREEZE_WRITE);
1516         down_write(&sb->s_umount);
1517 
1518         /* Now we go and block page faults... */
1519         sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1520         sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1521 
1522         /* All writers are done so after syncing there won't be dirty data */
1523         sync_filesystem(sb);
1524 
1525         /* Now wait for internal filesystem counter */
1526         sb->s_writers.frozen = SB_FREEZE_FS;
1527         sb_wait_write(sb, SB_FREEZE_FS);
1528 
1529         if (sb->s_op->freeze_fs) {
1530                 ret = sb->s_op->freeze_fs(sb);
1531                 if (ret) {
1532                         printk(KERN_ERR
1533                                 "VFS:Filesystem freeze failed\n");
1534                         sb->s_writers.frozen = SB_UNFROZEN;
1535                         sb_freeze_unlock(sb);
1536                         wake_up(&sb->s_writers.wait_unfrozen);
1537                         deactivate_locked_super(sb);
1538                         return ret;
1539                 }
1540         }
1541         /*
1542          * For debugging purposes so that fs can warn if it sees write activity
1543          * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
1544          */
1545         sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1546         lockdep_sb_freeze_release(sb);
1547         up_write(&sb->s_umount);
1548         return 0;
1549 }
1550 EXPORT_SYMBOL(freeze_super);
1551 
1552 /**
1553  * thaw_super -- unlock filesystem
1554  * @sb: the super to thaw
1555  *
1556  * Unlocks the filesystem and marks it writeable again after freeze_super().
1557  */
1558 static int thaw_super_locked(struct super_block *sb)
1559 {
1560         int error;
1561 
1562         if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
1563                 up_write(&sb->s_umount);
1564                 return -EINVAL;
1565         }
1566 
1567         if (sb_rdonly(sb)) {
1568                 sb->s_writers.frozen = SB_UNFROZEN;
1569                 goto out;
1570         }
1571 
1572         lockdep_sb_freeze_acquire(sb);
1573 
1574         if (sb->s_op->unfreeze_fs) {
1575                 error = sb->s_op->unfreeze_fs(sb);
1576                 if (error) {
1577                         printk(KERN_ERR
1578                                 "VFS:Filesystem thaw failed\n");
1579                         lockdep_sb_freeze_release(sb);
1580                         up_write(&sb->s_umount);
1581                         return error;
1582                 }
1583         }
1584 
1585         sb->s_writers.frozen = SB_UNFROZEN;
1586         sb_freeze_unlock(sb);
1587 out:
1588         wake_up(&sb->s_writers.wait_unfrozen);
1589         deactivate_locked_super(sb);
1590         return 0;
1591 }
1592 
1593 int thaw_super(struct super_block *sb)
1594 {
1595         down_write(&sb->s_umount);
1596         return thaw_super_locked(sb);
1597 }
1598 EXPORT_SYMBOL(thaw_super);
1599 

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