path: root/fs/super.c (plain)
blob: de136ed3105bdb1d7e287f3d6a4fb5f5bf2d4612

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	* We don't call trylock_super() here as it is a scalability bottleneck,
123	* so we're exposed to partial setup state. The shrinker rwsem does not
124	* protect filesystem operations backing list_lru_shrink_count() or
125	* s_op->nr_cached_objects(). Counts can change between
126	* super_cache_count and super_cache_scan, so we really don't need locks
127	* here.
128	*
129	* However, if we are currently mounting the superblock, the underlying
130	* filesystem might be in a state of partial construction and hence it
131	* is dangerous to access it. trylock_super() uses a MS_BORN check to
132	* avoid this situation, so do the same here. The memory barrier is
133	* matched with the one in mount_fs() as we don't hold locks here.
134	*/
135	if (!(sb->s_flags & MS_BORN))
136	return 0;
137	smp_rmb();
138
139	if (sb->s_op && sb->s_op->nr_cached_objects)
140	total_objects = sb->s_op->nr_cached_objects(sb, sc);
141
142	total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
143	total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
144
145	total_objects = vfs_pressure_ratio(total_objects);
146	return total_objects;
147	}
148
149	static void destroy_super_work(struct work_struct *work)
150	{
151	struct super_block *s = container_of(work, struct super_block,
152	destroy_work);
153	int i;
154
155	for (i = 0; i < SB_FREEZE_LEVELS; i++)
156	percpu_free_rwsem(&s->s_writers.rw_sem[i]);
157	kfree(s);
158	}
159
160	static void destroy_super_rcu(struct rcu_head *head)
161	{
162	struct super_block *s = container_of(head, struct super_block, rcu);
163	INIT_WORK(&s->destroy_work, destroy_super_work);
164	schedule_work(&s->destroy_work);
165	}
166
167	/**
168	* destroy_super - frees a superblock
169	* @s: superblock to free
170	*
171	* Frees a superblock.
172	*/
173	static void destroy_super(struct super_block *s)
174	{
175	list_lru_destroy(&s->s_dentry_lru);
176	list_lru_destroy(&s->s_inode_lru);
177	security_sb_free(s);
178	WARN_ON(!list_empty(&s->s_mounts));
179	put_user_ns(s->s_user_ns);
180	kfree(s->s_subtype);
181	kfree(s->s_options);
182	call_rcu(&s->rcu, destroy_super_rcu);
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
207	if (security_sb_alloc(s))
208	goto fail;
209
210	for (i = 0; i < SB_FREEZE_LEVELS; i++) {
211	if (__percpu_init_rwsem(&s->s_writers.rw_sem[i],
212	sb_writers_name[i],
213	&type->s_writers_key[i]))
214	goto fail;
215	}
216	init_waitqueue_head(&s->s_writers.wait_unfrozen);
217	s->s_bdi = &noop_backing_dev_info;
218	s->s_flags = flags;
219	if (s->s_user_ns != &init_user_ns)
220	s->s_iflags |= SB_I_NODEV;
221	INIT_HLIST_NODE(&s->s_instances);
222	INIT_HLIST_BL_HEAD(&s->s_anon);
223	mutex_init(&s->s_sync_lock);
224	INIT_LIST_HEAD(&s->s_inodes);
225	spin_lock_init(&s->s_inode_list_lock);
226	INIT_LIST_HEAD(&s->s_inodes_wb);
227	spin_lock_init(&s->s_inode_wblist_lock);
228
229	if (list_lru_init_memcg(&s->s_dentry_lru))
230	goto fail;
231	if (list_lru_init_memcg(&s->s_inode_lru))
232	goto fail;
233
234	init_rwsem(&s->s_umount);
235	lockdep_set_class(&s->s_umount, &type->s_umount_key);
236	/*
237	* sget() can have s_umount recursion.
238	*
239	* When it cannot find a suitable sb, it allocates a new
240	* one (this one), and tries again to find a suitable old
241	* one.
242	*
243	* In case that succeeds, it will acquire the s_umount
244	* lock of the old one. Since these are clearly distrinct
245	* locks, and this object isn't exposed yet, there's no
246	* risk of deadlocks.
247	*
248	* Annotate this by putting this lock in a different
249	* subclass.
250	*/
251	down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
252	s->s_count = 1;
253	atomic_set(&s->s_active, 1);
254	mutex_init(&s->s_vfs_rename_mutex);
255	lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
256	mutex_init(&s->s_dquot.dqio_mutex);
257	mutex_init(&s->s_dquot.dqonoff_mutex);
258	s->s_maxbytes = MAX_NON_LFS;
259	s->s_op = &default_op;
260	s->s_time_gran = 1000000000;
261	s->cleancache_poolid = CLEANCACHE_NO_POOL;
262
263	s->s_shrink.seeks = DEFAULT_SEEKS;
264	s->s_shrink.scan_objects = super_cache_scan;
265	s->s_shrink.count_objects = super_cache_count;
266	s->s_shrink.batch = 1024;
267	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
268	return s;
269
270	fail:
271	destroy_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 *sb)
281	{
282	if (!--sb->s_count) {
283	list_del_init(&sb->s_list);
284	destroy_super(sb);
285	}
286	}
287
288	/**
289	* put_super - drop a temporary reference to superblock
290	* @sb: superblock in question
291	*
292	* Drops a temporary reference, frees superblock if there's no
293	* references left.
294	*/
295	static void put_super(struct super_block *sb)
296	{
297	spin_lock(&sb_lock);
298	__put_super(sb);
299	spin_unlock(&sb_lock);
300	}
301
302
303	/**
304	* deactivate_locked_super - drop an active reference to superblock
305	* @s: superblock to deactivate
306	*
307	* Drops an active reference to superblock, converting it into a temporary
308	* one if there is no other active references left. In that case we
309	* tell fs driver to shut it down and drop the temporary reference we
310	* had just acquired.
311	*
312	* Caller holds exclusive lock on superblock; that lock is released.
313	*/
314	void deactivate_locked_super(struct super_block *s)
315	{
316	struct file_system_type *fs = s->s_type;
317	if (atomic_dec_and_test(&s->s_active)) {
318	cleancache_invalidate_fs(s);
319	unregister_shrinker(&s->s_shrink);
320	fs->kill_sb(s);
321
322	/*
323	* Since list_lru_destroy() may sleep, we cannot call it from
324	* put_super(), where we hold the sb_lock. Therefore we destroy
325	* the lru lists right now.
326	*/
327	list_lru_destroy(&s->s_dentry_lru);
328	list_lru_destroy(&s->s_inode_lru);
329
330	put_filesystem(fs);
331	put_super(s);
332	} else {
333	up_write(&s->s_umount);
334	}
335	}
336
337	EXPORT_SYMBOL(deactivate_locked_super);
338
339	/**
340	* deactivate_super - drop an active reference to superblock
341	* @s: superblock to deactivate
342	*
343	* Variant of deactivate_locked_super(), except that superblock is *not*
344	* locked by caller. If we are going to drop the final active reference,
345	* lock will be acquired prior to that.
346	*/
347	void deactivate_super(struct super_block *s)
348	{
349	if (!atomic_add_unless(&s->s_active, -1, 1)) {
350	down_write(&s->s_umount);
351	deactivate_locked_super(s);
352	}
353	}
354
355	EXPORT_SYMBOL(deactivate_super);
356
357	/**
358	* grab_super - acquire an active reference
359	* @s: reference we are trying to make active
360	*
361	* Tries to acquire an active reference. grab_super() is used when we
362	* had just found a superblock in super_blocks or fs_type->fs_supers
363	* and want to turn it into a full-blown active reference. grab_super()
364	* is called with sb_lock held and drops it. Returns 1 in case of
365	* success, 0 if we had failed (superblock contents was already dead or
366	* dying when grab_super() had been called). Note that this is only
367	* called for superblocks not in rundown mode (== ones still on ->fs_supers
368	* of their type), so increment of ->s_count is OK here.
369	*/
370	static int grab_super(struct super_block *s) __releases(sb_lock)
371	{
372	s->s_count++;
373	spin_unlock(&sb_lock);
374	down_write(&s->s_umount);
375	if ((s->s_flags & MS_BORN) && atomic_inc_not_zero(&s->s_active)) {
376	put_super(s);
377	return 1;
378	}
379	up_write(&s->s_umount);
380	put_super(s);
381	return 0;
382	}
383
384	/*
385	* trylock_super - try to grab ->s_umount shared
386	* @sb: reference we are trying to grab
387	*
388	* Try to prevent fs shutdown. This is used in places where we
389	* cannot take an active reference but we need to ensure that the
390	* filesystem is not shut down while we are working on it. It returns
391	* false if we cannot acquire s_umount or if we lose the race and
392	* filesystem already got into shutdown, and returns true with the s_umount
393	* lock held in read mode in case of success. On successful return,
394	* the caller must drop the s_umount lock when done.
395	*
396	* Note that unlike get_super() et.al. this one does *not* bump ->s_count.
397	* The reason why it's safe is that we are OK with doing trylock instead
398	* of down_read(). There's a couple of places that are OK with that, but
399	* it's very much not a general-purpose interface.
400	*/
401	bool trylock_super(struct super_block *sb)
402	{
403	if (down_read_trylock(&sb->s_umount)) {
404	if (!hlist_unhashed(&sb->s_instances) &&
405	sb->s_root && (sb->s_flags & MS_BORN))
406	return true;
407	up_read(&sb->s_umount);
408	}
409
410	return false;
411	}
412
413	/**
414	* generic_shutdown_super - common helper for ->kill_sb()
415	* @sb: superblock to kill
416	*
417	* generic_shutdown_super() does all fs-independent work on superblock
418	* shutdown. Typical ->kill_sb() should pick all fs-specific objects
419	* that need destruction out of superblock, call generic_shutdown_super()
420	* and release aforementioned objects. Note: dentries and inodes _are_
421	* taken care of and do not need specific handling.
422	*
423	* Upon calling this function, the filesystem may no longer alter or
424	* rearrange the set of dentries belonging to this super_block, nor may it
425	* change the attachments of dentries to inodes.
426	*/
427	void generic_shutdown_super(struct super_block *sb)
428	{
429	const struct super_operations *sop = sb->s_op;
430
431	if (sb->s_root) {
432	shrink_dcache_for_umount(sb);
433	sync_filesystem(sb);
434	sb->s_flags &= ~MS_ACTIVE;
435
436	fsnotify_unmount_inodes(sb);
437	cgroup_writeback_umount();
438
439	evict_inodes(sb);
440
441	if (sb->s_dio_done_wq) {
442	destroy_workqueue(sb->s_dio_done_wq);
443	sb->s_dio_done_wq = NULL;
444	}
445
446	if (sop->put_super)
447	sop->put_super(sb);
448
449	if (!list_empty(&sb->s_inodes)) {
450	printk("VFS: Busy inodes after unmount of %s. "
451	"Self-destruct in 5 seconds. Have a nice day...\n",
452	sb->s_id);
453	}
454	}
455	spin_lock(&sb_lock);
456	/* should be initialized for __put_super_and_need_restart() */
457	hlist_del_init(&sb->s_instances);
458	spin_unlock(&sb_lock);
459	up_write(&sb->s_umount);
460	}
461
462	EXPORT_SYMBOL(generic_shutdown_super);
463
464	/**
465	* sget_userns - find or create a superblock
466	* @type: filesystem type superblock should belong to
467	* @test: comparison callback
468	* @set: setup callback
469	* @flags: mount flags
470	* @user_ns: User namespace for the super_block
471	* @data: argument to each of them
472	*/
473	struct super_block *sget_userns(struct file_system_type *type,
474	int (*test)(struct super_block *,void *),
475	int (*set)(struct super_block *,void *),
476	int flags, struct user_namespace *user_ns,
477	void *data)
478	{
479	struct super_block *s = NULL;
480	struct super_block *old;
481	int err;
482
483	if (!(flags & (MS_KERNMOUNT|MS_SUBMOUNT)) &&
484	!(type->fs_flags & FS_USERNS_MOUNT) &&
485	!capable(CAP_SYS_ADMIN))
486	return ERR_PTR(-EPERM);
487	retry:
488	spin_lock(&sb_lock);
489	if (test) {
490	hlist_for_each_entry(old, &type->fs_supers, s_instances) {
491	if (!test(old, data))
492	continue;
493	if (user_ns != old->s_user_ns) {
494	spin_unlock(&sb_lock);
495	if (s) {
496	up_write(&s->s_umount);
497	destroy_super(s);
498	}
499	return ERR_PTR(-EBUSY);
500	}
501	if (!grab_super(old))
502	goto retry;
503	if (s) {
504	up_write(&s->s_umount);
505	destroy_super(s);
506	s = NULL;
507	}
508	return old;
509	}
510	}
511	if (!s) {
512	spin_unlock(&sb_lock);
513	s = alloc_super(type, (flags & ~MS_SUBMOUNT), user_ns);
514	if (!s)
515	return ERR_PTR(-ENOMEM);
516	goto retry;
517	}
518
519	err = set(s, data);
520	if (err) {
521	spin_unlock(&sb_lock);
522	up_write(&s->s_umount);
523	destroy_super(s);
524	return ERR_PTR(err);
525	}
526	s->s_type = type;
527	strlcpy(s->s_id, type->name, sizeof(s->s_id));
528	list_add_tail(&s->s_list, &super_blocks);
529	hlist_add_head(&s->s_instances, &type->fs_supers);
530	spin_unlock(&sb_lock);
531	get_filesystem(type);
532	err = register_shrinker(&s->s_shrink);
533	if (err) {
534	deactivate_locked_super(s);
535	s = ERR_PTR(err);
536	}
537	return s;
538	}
539
540	EXPORT_SYMBOL(sget_userns);
541
542	/**
543	* sget - find or create a superblock
544	* @type: filesystem type superblock should belong to
545	* @test: comparison callback
546	* @set: setup callback
547	* @flags: mount flags
548	* @data: argument to each of them
549	*/
550	struct super_block *sget(struct file_system_type *type,
551	int (*test)(struct super_block *,void *),
552	int (*set)(struct super_block *,void *),
553	int flags,
554	void *data)
555	{
556	struct user_namespace *user_ns = current_user_ns();
557
558	/* We don't yet pass the user namespace of the parent
559	* mount through to here so always use &init_user_ns
560	* until that changes.
561	*/
562	if (flags & MS_SUBMOUNT)
563	user_ns = &init_user_ns;
564
565	/* Ensure the requestor has permissions over the target filesystem */
566	if (!(flags & (MS_KERNMOUNT|MS_SUBMOUNT)) && !ns_capable(user_ns, CAP_SYS_ADMIN))
567	return ERR_PTR(-EPERM);
568
569	return sget_userns(type, test, set, flags, user_ns, data);
570	}
571
572	EXPORT_SYMBOL(sget);
573
574	void drop_super(struct super_block *sb)
575	{
576	up_read(&sb->s_umount);
577	put_super(sb);
578	}
579
580	EXPORT_SYMBOL(drop_super);
581
582	/**
583	* iterate_supers - call function for all active superblocks
584	* @f: function to call
585	* @arg: argument to pass to it
586	*
587	* Scans the superblock list and calls given function, passing it
588	* locked superblock and given argument.
589	*/
590	void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
591	{
592	struct super_block *sb, *p = NULL;
593
594	spin_lock(&sb_lock);
595	list_for_each_entry(sb, &super_blocks, s_list) {
596	if (hlist_unhashed(&sb->s_instances))
597	continue;
598	sb->s_count++;
599	spin_unlock(&sb_lock);
600
601	down_read(&sb->s_umount);
602	if (sb->s_root && (sb->s_flags & MS_BORN))
603	f(sb, arg);
604	up_read(&sb->s_umount);
605
606	spin_lock(&sb_lock);
607	if (p)
608	__put_super(p);
609	p = sb;
610	}
611	if (p)
612	__put_super(p);
613	spin_unlock(&sb_lock);
614	}
615
616	/**
617	* iterate_supers_type - call function for superblocks of given type
618	* @type: fs type
619	* @f: function to call
620	* @arg: argument to pass to it
621	*
622	* Scans the superblock list and calls given function, passing it
623	* locked superblock and given argument.
624	*/
625	void iterate_supers_type(struct file_system_type *type,
626	void (*f)(struct super_block *, void *), void *arg)
627	{
628	struct super_block *sb, *p = NULL;
629
630	spin_lock(&sb_lock);
631	hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
632	sb->s_count++;
633	spin_unlock(&sb_lock);
634
635	down_read(&sb->s_umount);
636	if (sb->s_root && (sb->s_flags & MS_BORN))
637	f(sb, arg);
638	up_read(&sb->s_umount);
639
640	spin_lock(&sb_lock);
641	if (p)
642	__put_super(p);
643	p = sb;
644	}
645	if (p)
646	__put_super(p);
647	spin_unlock(&sb_lock);
648	}
649
650	EXPORT_SYMBOL(iterate_supers_type);
651
652	/**
653	* get_super - get the superblock of a device
654	* @bdev: device to get the superblock for
655	*
656	* Scans the superblock list and finds the superblock of the file system
657	* mounted on the device given. %NULL is returned if no match is found.
658	*/
659
660	struct super_block *get_super(struct block_device *bdev)
661	{
662	struct super_block *sb;
663
664	if (!bdev)
665	return NULL;
666
667	spin_lock(&sb_lock);
668	rescan:
669	list_for_each_entry(sb, &super_blocks, s_list) {
670	if (hlist_unhashed(&sb->s_instances))
671	continue;
672	if (sb->s_bdev == bdev) {
673	sb->s_count++;
674	spin_unlock(&sb_lock);
675	down_read(&sb->s_umount);
676	/* still alive? */
677	if (sb->s_root && (sb->s_flags & MS_BORN))
678	return sb;
679	up_read(&sb->s_umount);
680	/* nope, got unmounted */
681	spin_lock(&sb_lock);
682	__put_super(sb);
683	goto rescan;
684	}
685	}
686	spin_unlock(&sb_lock);
687	return NULL;
688	}
689
690	EXPORT_SYMBOL(get_super);
691
692	/**
693	* get_super_thawed - get thawed superblock of a device
694	* @bdev: device to get the superblock for
695	*
696	* Scans the superblock list and finds the superblock of the file system
697	* mounted on the device. The superblock is returned once it is thawed
698	* (or immediately if it was not frozen). %NULL is returned if no match
699	* is found.
700	*/
701	struct super_block *get_super_thawed(struct block_device *bdev)
702	{
703	while (1) {
704	struct super_block *s = get_super(bdev);
705	if (!s || s->s_writers.frozen == SB_UNFROZEN)
706	return s;
707	up_read(&s->s_umount);
708	wait_event(s->s_writers.wait_unfrozen,
709	s->s_writers.frozen == SB_UNFROZEN);
710	put_super(s);
711	}
712	}
713	EXPORT_SYMBOL(get_super_thawed);
714
715	/**
716	* get_active_super - get an active reference to 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. Returns the superblock with an active
721	* reference or %NULL if none was found.
722	*/
723	struct super_block *get_active_super(struct block_device *bdev)
724	{
725	struct super_block *sb;
726
727	if (!bdev)
728	return NULL;
729
730	restart:
731	spin_lock(&sb_lock);
732	list_for_each_entry(sb, &super_blocks, s_list) {
733	if (hlist_unhashed(&sb->s_instances))
734	continue;
735	if (sb->s_bdev == bdev) {
736	if (!grab_super(sb))
737	goto restart;
738	up_write(&sb->s_umount);
739	return sb;
740	}
741	}
742	spin_unlock(&sb_lock);
743	return NULL;
744	}
745
746	struct super_block *user_get_super(dev_t dev)
747	{
748	struct super_block *sb;
749
750	spin_lock(&sb_lock);
751	rescan:
752	list_for_each_entry(sb, &super_blocks, s_list) {
753	if (hlist_unhashed(&sb->s_instances))
754	continue;
755	if (sb->s_dev == dev) {
756	sb->s_count++;
757	spin_unlock(&sb_lock);
758	down_read(&sb->s_umount);
759	/* still alive? */
760	if (sb->s_root && (sb->s_flags & MS_BORN))
761	return sb;
762	up_read(&sb->s_umount);
763	/* nope, got unmounted */
764	spin_lock(&sb_lock);
765	__put_super(sb);
766	goto rescan;
767	}
768	}
769	spin_unlock(&sb_lock);
770	return NULL;
771	}
772
773	/**
774	* do_remount_sb2 - asks filesystem to change mount options.
775	* @mnt: mount we are looking at
776	* @sb: superblock in question
777	* @flags: numeric part of options
778	* @data: the rest of options
779	* @force: whether or not to force the change
780	*
781	* Alters the mount options of a mounted file system.
782	*/
783	int do_remount_sb2(struct vfsmount *mnt, struct super_block *sb, int flags, void *data, int force)
784	{
785	int retval;
786	int remount_ro;
787
788	if (sb->s_writers.frozen != SB_UNFROZEN)
789	return -EBUSY;
790
791	#ifdef CONFIG_BLOCK
792	if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
793	return -EACCES;
794	#endif
795
796	remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
797
798	if (remount_ro) {
799	if (!hlist_empty(&sb->s_pins)) {
800	up_write(&sb->s_umount);
801	group_pin_kill(&sb->s_pins);
802	down_write(&sb->s_umount);
803	if (!sb->s_root)
804	return 0;
805	if (sb->s_writers.frozen != SB_UNFROZEN)
806	return -EBUSY;
807	remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
808	}
809	}
810	shrink_dcache_sb(sb);
811
812	/* If we are remounting RDONLY and current sb is read/write,
813	make sure there are no rw files opened */
814	if (remount_ro) {
815	if (force) {
816	sb->s_readonly_remount = 1;
817	smp_wmb();
818	} else {
819	retval = sb_prepare_remount_readonly(sb);
820	if (retval)
821	return retval;
822	}
823	}
824
825	if (mnt && sb->s_op->remount_fs2) {
826	retval = sb->s_op->remount_fs2(mnt, sb, &flags, data);
827	if (retval) {
828	if (!force)
829	goto cancel_readonly;
830	/* If forced remount, go ahead despite any errors */
831	WARN(1, "forced remount of a %s fs returned %i\n",
832	sb->s_type->name, retval);
833	}
834	} else if (sb->s_op->remount_fs) {
835	retval = sb->s_op->remount_fs(sb, &flags, data);
836	if (retval) {
837	if (!force)
838	goto cancel_readonly;
839	/* If forced remount, go ahead despite any errors */
840	WARN(1, "forced remount of a %s fs returned %i\n",
841	sb->s_type->name, retval);
842	}
843	}
844	sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
845	/* Needs to be ordered wrt mnt_is_readonly() */
846	smp_wmb();
847	sb->s_readonly_remount = 0;
848
849	/*
850	* Some filesystems modify their metadata via some other path than the
851	* bdev buffer cache (eg. use a private mapping, or directories in
852	* pagecache, etc). Also file data modifications go via their own
853	* mappings. So If we try to mount readonly then copy the filesystem
854	* from bdev, we could get stale data, so invalidate it to give a best
855	* effort at coherency.
856	*/
857	if (remount_ro && sb->s_bdev)
858	invalidate_bdev(sb->s_bdev);
859	return 0;
860
861	cancel_readonly:
862	sb->s_readonly_remount = 0;
863	return retval;
864	}
865
866	int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
867	{
868	return do_remount_sb2(NULL, sb, flags, data, force);
869	}
870
871	static void do_emergency_remount(struct work_struct *work)
872	{
873	struct super_block *sb, *p = NULL;
874
875	spin_lock(&sb_lock);
876	list_for_each_entry_reverse(sb, &super_blocks, s_list) {
877	if (hlist_unhashed(&sb->s_instances))
878	continue;
879	sb->s_count++;
880	spin_unlock(&sb_lock);
881	down_write(&sb->s_umount);
882	if (sb->s_root && sb->s_bdev && (sb->s_flags & MS_BORN) &&
883	!(sb->s_flags & MS_RDONLY)) {
884	/*
885	* What lock protects sb->s_flags??
886	*/
887	do_remount_sb(sb, MS_RDONLY, NULL, 1);
888	}
889	up_write(&sb->s_umount);
890	spin_lock(&sb_lock);
891	if (p)
892	__put_super(p);
893	p = sb;
894	}
895	if (p)
896	__put_super(p);
897	spin_unlock(&sb_lock);
898	kfree(work);
899	printk("Emergency Remount complete\n");
900	}
901
902	void emergency_remount(void)
903	{
904	struct work_struct *work;
905
906	work = kmalloc(sizeof(*work), GFP_ATOMIC);
907	if (work) {
908	INIT_WORK(work, do_emergency_remount);
909	schedule_work(work);
910	}
911	}
912
913	/*
914	* Unnamed block devices are dummy devices used by virtual
915	* filesystems which don't use real block-devices. -- jrs
916	*/
917
918	static DEFINE_IDA(unnamed_dev_ida);
919	static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
920	/* Many userspace utilities consider an FSID of 0 invalid.
921	* Always return at least 1 from get_anon_bdev.
922	*/
923	static int unnamed_dev_start = 1;
924
925	int get_anon_bdev(dev_t *p)
926	{
927	int dev;
928	int error;
929
930	retry:
931	if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
932	return -ENOMEM;
933	spin_lock(&unnamed_dev_lock);
934	error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
935	if (!error)
936	unnamed_dev_start = dev + 1;
937	spin_unlock(&unnamed_dev_lock);
938	if (error == -EAGAIN)
939	/* We raced and lost with another CPU. */
940	goto retry;
941	else if (error)
942	return -EAGAIN;
943
944	if (dev >= (1 << MINORBITS)) {
945	spin_lock(&unnamed_dev_lock);
946	ida_remove(&unnamed_dev_ida, dev);
947	if (unnamed_dev_start > dev)
948	unnamed_dev_start = dev;
949	spin_unlock(&unnamed_dev_lock);
950	return -EMFILE;
951	}
952	*p = MKDEV(0, dev & MINORMASK);
953	return 0;
954	}
955	EXPORT_SYMBOL(get_anon_bdev);
956
957	void free_anon_bdev(dev_t dev)
958	{
959	int slot = MINOR(dev);
960	spin_lock(&unnamed_dev_lock);
961	ida_remove(&unnamed_dev_ida, slot);
962	if (slot < unnamed_dev_start)
963	unnamed_dev_start = slot;
964	spin_unlock(&unnamed_dev_lock);
965	}
966	EXPORT_SYMBOL(free_anon_bdev);
967
968	int set_anon_super(struct super_block *s, void *data)
969	{
970	return get_anon_bdev(&s->s_dev);
971	}
972
973	EXPORT_SYMBOL(set_anon_super);
974
975	void kill_anon_super(struct super_block *sb)
976	{
977	dev_t dev = sb->s_dev;
978	generic_shutdown_super(sb);
979	free_anon_bdev(dev);
980	}
981
982	EXPORT_SYMBOL(kill_anon_super);
983
984	void kill_litter_super(struct super_block *sb)
985	{
986	if (sb->s_root)
987	d_genocide(sb->s_root);
988	kill_anon_super(sb);
989	}
990
991	EXPORT_SYMBOL(kill_litter_super);
992
993	static int ns_test_super(struct super_block *sb, void *data)
994	{
995	return sb->s_fs_info == data;
996	}
997
998	static int ns_set_super(struct super_block *sb, void *data)
999	{
1000	sb->s_fs_info = data;
1001	return set_anon_super(sb, NULL);
1002	}
1003
1004	struct dentry *mount_ns(struct file_system_type *fs_type,
1005	int flags, void *data, void *ns, struct user_namespace *user_ns,
1006	int (*fill_super)(struct super_block *, void *, int))
1007	{
1008	struct super_block *sb;
1009
1010	/* Don't allow mounting unless the caller has CAP_SYS_ADMIN
1011	* over the namespace.
1012	*/
1013	if (!(flags & MS_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN))
1014	return ERR_PTR(-EPERM);
1015
1016	sb = sget_userns(fs_type, ns_test_super, ns_set_super, flags,
1017	user_ns, ns);
1018	if (IS_ERR(sb))
1019	return ERR_CAST(sb);
1020
1021	if (!sb->s_root) {
1022	int err;
1023	err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
1024	if (err) {
1025	deactivate_locked_super(sb);
1026	return ERR_PTR(err);
1027	}
1028
1029	sb->s_flags |= MS_ACTIVE;
1030	}
1031
1032	return dget(sb->s_root);
1033	}
1034
1035	EXPORT_SYMBOL(mount_ns);
1036
1037	#ifdef CONFIG_BLOCK
1038	static int set_bdev_super(struct super_block *s, void *data)
1039	{
1040	s->s_bdev = data;
1041	s->s_dev = s->s_bdev->bd_dev;
1042
1043	/*
1044	* We set the bdi here to the queue backing, file systems can
1045	* overwrite this in ->fill_super()
1046	*/
1047	s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
1048	return 0;
1049	}
1050
1051	static int test_bdev_super(struct super_block *s, void *data)
1052	{
1053	return (void *)s->s_bdev == data;
1054	}
1055
1056	struct dentry *mount_bdev(struct file_system_type *fs_type,
1057	int flags, const char *dev_name, void *data,
1058	int (*fill_super)(struct super_block *, void *, int))
1059	{
1060	struct block_device *bdev;
1061	struct super_block *s;
1062	fmode_t mode = FMODE_READ | FMODE_EXCL;
1063	int error = 0;
1064
1065	if (!(flags & MS_RDONLY))
1066	mode |= FMODE_WRITE;
1067
1068	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
1069	if (IS_ERR(bdev))
1070	return ERR_CAST(bdev);
1071
1072	/*
1073	* once the super is inserted into the list by sget, s_umount
1074	* will protect the lockfs code from trying to start a snapshot
1075	* while we are mounting
1076	*/
1077	mutex_lock(&bdev->bd_fsfreeze_mutex);
1078	if (bdev->bd_fsfreeze_count > 0) {
1079	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1080	error = -EBUSY;
1081	goto error_bdev;
1082	}
1083	s = sget(fs_type, test_bdev_super, set_bdev_super, flags | MS_NOSEC,
1084	bdev);
1085	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1086	if (IS_ERR(s))
1087	goto error_s;
1088
1089	if (s->s_root) {
1090	if ((flags ^ s->s_flags) & MS_RDONLY) {
1091	deactivate_locked_super(s);
1092	error = -EBUSY;
1093	goto error_bdev;
1094	}
1095
1096	/*
1097	* s_umount nests inside bd_mutex during
1098	* __invalidate_device(). blkdev_put() acquires
1099	* bd_mutex and can't be called under s_umount. Drop
1100	* s_umount temporarily. This is safe as we're
1101	* holding an active reference.
1102	*/
1103	up_write(&s->s_umount);
1104	blkdev_put(bdev, mode);
1105	down_write(&s->s_umount);
1106	} else {
1107	s->s_mode = mode;
1108	snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1109	sb_set_blocksize(s, block_size(bdev));
1110	error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1111	if (error) {
1112	deactivate_locked_super(s);
1113	goto error;
1114	}
1115
1116	s->s_flags |= MS_ACTIVE;
1117	bdev->bd_super = s;
1118	}
1119
1120	return dget(s->s_root);
1121
1122	error_s:
1123	error = PTR_ERR(s);
1124	error_bdev:
1125	blkdev_put(bdev, mode);
1126	error:
1127	return ERR_PTR(error);
1128	}
1129	EXPORT_SYMBOL(mount_bdev);
1130
1131	void kill_block_super(struct super_block *sb)
1132	{
1133	struct block_device *bdev = sb->s_bdev;
1134	fmode_t mode = sb->s_mode;
1135
1136	bdev->bd_super = NULL;
1137	generic_shutdown_super(sb);
1138	sync_blockdev(bdev);
1139	WARN_ON_ONCE(!(mode & FMODE_EXCL));
1140	blkdev_put(bdev, mode | FMODE_EXCL);
1141	}
1142
1143	EXPORT_SYMBOL(kill_block_super);
1144	#endif
1145
1146	struct dentry *mount_nodev(struct file_system_type *fs_type,
1147	int flags, void *data,
1148	int (*fill_super)(struct super_block *, void *, int))
1149	{
1150	int error;
1151	struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1152
1153	if (IS_ERR(s))
1154	return ERR_CAST(s);
1155
1156	error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1157	if (error) {
1158	deactivate_locked_super(s);
1159	return ERR_PTR(error);
1160	}
1161	s->s_flags |= MS_ACTIVE;
1162	return dget(s->s_root);
1163	}
1164	EXPORT_SYMBOL(mount_nodev);
1165
1166	static int compare_single(struct super_block *s, void *p)
1167	{
1168	return 1;
1169	}
1170
1171	struct dentry *mount_single(struct file_system_type *fs_type,
1172	int flags, void *data,
1173	int (*fill_super)(struct super_block *, void *, int))
1174	{
1175	struct super_block *s;
1176	int error;
1177
1178	s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1179	if (IS_ERR(s))
1180	return ERR_CAST(s);
1181	if (!s->s_root) {
1182	error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1183	if (error) {
1184	deactivate_locked_super(s);
1185	return ERR_PTR(error);
1186	}
1187	s->s_flags |= MS_ACTIVE;
1188	} else {
1189	do_remount_sb(s, flags, data, 0);
1190	}
1191	return dget(s->s_root);
1192	}
1193	EXPORT_SYMBOL(mount_single);
1194
1195	struct dentry *
1196	mount_fs(struct file_system_type *type, int flags, const char *name, struct vfsmount *mnt, void *data)
1197	{
1198	struct dentry *root;
1199	struct super_block *sb;
1200	char *secdata = NULL;
1201	int error = -ENOMEM;
1202
1203	if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
1204	secdata = alloc_secdata();
1205	if (!secdata)
1206	goto out;
1207
1208	error = security_sb_copy_data(data, secdata);
1209	if (error)
1210	goto out_free_secdata;
1211	}
1212
1213	if (type->mount2)
1214	root = type->mount2(mnt, type, flags, name, data);
1215	else
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
1225	/*
1226	* Write barrier is for super_cache_count(). We place it before setting
1227	* MS_BORN as the data dependency between the two functions is the
1228	* superblock structure contents that we just set up, not the MS_BORN
1229	* flag.
1230	*/
1231	smp_wmb();
1232	sb->s_flags |= MS_BORN;
1233
1234	error = security_sb_kern_mount(sb, flags, secdata);
1235	if (error)
1236	goto out_sb;
1237
1238	/*
1239	* filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1240	* but s_maxbytes was an unsigned long long for many releases. Throw
1241	* this warning for a little while to try and catch filesystems that
1242	* violate this rule.
1243	*/
1244	WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1245	"negative value (%lld)\n", type->name, sb->s_maxbytes);
1246
1247	up_write(&sb->s_umount);
1248	free_secdata(secdata);
1249	return root;
1250	out_sb:
1251	dput(root);
1252	deactivate_locked_super(sb);
1253	out_free_secdata:
1254	free_secdata(secdata);
1255	out:
1256	return ERR_PTR(error);
1257	}
1258
1259	/*
1260	* This is an internal function, please use sb_end_{write,pagefault,intwrite}
1261	* instead.
1262	*/
1263	void __sb_end_write(struct super_block *sb, int level)
1264	{
1265	percpu_up_read(sb->s_writers.rw_sem + level-1);
1266	}
1267	EXPORT_SYMBOL(__sb_end_write);
1268
1269	/*
1270	* This is an internal function, please use sb_start_{write,pagefault,intwrite}
1271	* instead.
1272	*/
1273	int __sb_start_write(struct super_block *sb, int level, bool wait)
1274	{
1275	bool force_trylock = false;
1276	int ret = 1;
1277
1278	#ifdef CONFIG_LOCKDEP
1279	/*
1280	* We want lockdep to tell us about possible deadlocks with freezing
1281	* but it's it bit tricky to properly instrument it. Getting a freeze
1282	* protection works as getting a read lock but there are subtle
1283	* problems. XFS for example gets freeze protection on internal level
1284	* twice in some cases, which is OK only because we already hold a
1285	* freeze protection also on higher level. Due to these cases we have
1286	* to use wait == F (trylock mode) which must not fail.
1287	*/
1288	if (wait) {
1289	int i;
1290
1291	for (i = 0; i < level - 1; i++)
1292	if (percpu_rwsem_is_held(sb->s_writers.rw_sem + i)) {
1293	force_trylock = true;
1294	break;
1295	}
1296	}
1297	#endif
1298	if (wait && !force_trylock)
1299	percpu_down_read(sb->s_writers.rw_sem + level-1);
1300	else
1301	ret = percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
1302
1303	WARN_ON(force_trylock && !ret);
1304	return ret;
1305	}
1306	EXPORT_SYMBOL(__sb_start_write);
1307
1308	/**
1309	* sb_wait_write - wait until all writers to given file system finish
1310	* @sb: the super for which we wait
1311	* @level: type of writers we wait for (normal vs page fault)
1312	*
1313	* This function waits until there are no writers of given type to given file
1314	* system.
1315	*/
1316	static void sb_wait_write(struct super_block *sb, int level)
1317	{
1318	percpu_down_write(sb->s_writers.rw_sem + level-1);
1319	}
1320
1321	/*
1322	* We are going to return to userspace and forget about these locks, the
1323	* ownership goes to the caller of thaw_super() which does unlock().
1324	*/
1325	static void lockdep_sb_freeze_release(struct super_block *sb)
1326	{
1327	int level;
1328
1329	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1330	percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1331	}
1332
1333	/*
1334	* Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
1335	*/
1336	static void lockdep_sb_freeze_acquire(struct super_block *sb)
1337	{
1338	int level;
1339
1340	for (level = 0; level < SB_FREEZE_LEVELS; ++level)
1341	percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1342	}
1343
1344	static void sb_freeze_unlock(struct super_block *sb)
1345	{
1346	int level;
1347
1348	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1349	percpu_up_write(sb->s_writers.rw_sem + level);
1350	}
1351
1352	/**
1353	* freeze_super - lock the filesystem and force it into a consistent state
1354	* @sb: the super to lock
1355	*
1356	* Syncs the super to make sure the filesystem is consistent and calls the fs's
1357	* freeze_fs. Subsequent calls to this without first thawing the fs will return
1358	* -EBUSY.
1359	*
1360	* During this function, sb->s_writers.frozen goes through these values:
1361	*
1362	* SB_UNFROZEN: File system is normal, all writes progress as usual.
1363	*
1364	* SB_FREEZE_WRITE: The file system is in the process of being frozen. New
1365	* writes should be blocked, though page faults are still allowed. We wait for
1366	* all writes to complete and then proceed to the next stage.
1367	*
1368	* SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1369	* but internal fs threads can still modify the filesystem (although they
1370	* should not dirty new pages or inodes), writeback can run etc. After waiting
1371	* for all running page faults we sync the filesystem which will clean all
1372	* dirty pages and inodes (no new dirty pages or inodes can be created when
1373	* sync is running).
1374	*
1375	* SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1376	* modification are blocked (e.g. XFS preallocation truncation on inode
1377	* reclaim). This is usually implemented by blocking new transactions for
1378	* filesystems that have them and need this additional guard. After all
1379	* internal writers are finished we call ->freeze_fs() to finish filesystem
1380	* freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1381	* mostly auxiliary for filesystems to verify they do not modify frozen fs.
1382	*
1383	* sb->s_writers.frozen is protected by sb->s_umount.
1384	*/
1385	int freeze_super(struct super_block *sb)
1386	{
1387	int ret;
1388
1389	atomic_inc(&sb->s_active);
1390	down_write(&sb->s_umount);
1391	if (sb->s_writers.frozen != SB_UNFROZEN) {
1392	deactivate_locked_super(sb);
1393	return -EBUSY;
1394	}
1395
1396	if (!(sb->s_flags & MS_BORN)) {
1397	up_write(&sb->s_umount);
1398	return 0; /* sic - it's "nothing to do" */
1399	}
1400
1401	if (sb->s_flags & MS_RDONLY) {
1402	/* Nothing to do really... */
1403	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1404	up_write(&sb->s_umount);
1405	return 0;
1406	}
1407
1408	sb->s_writers.frozen = SB_FREEZE_WRITE;
1409	/* Release s_umount to preserve sb_start_write -> s_umount ordering */
1410	up_write(&sb->s_umount);
1411	sb_wait_write(sb, SB_FREEZE_WRITE);
1412	down_write(&sb->s_umount);
1413
1414	/* Now we go and block page faults... */
1415	sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1416	sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1417
1418	/* All writers are done so after syncing there won't be dirty data */
1419	sync_filesystem(sb);
1420
1421	/* Now wait for internal filesystem counter */
1422	sb->s_writers.frozen = SB_FREEZE_FS;
1423	sb_wait_write(sb, SB_FREEZE_FS);
1424
1425	if (sb->s_op->freeze_fs) {
1426	ret = sb->s_op->freeze_fs(sb);
1427	if (ret) {
1428	printk(KERN_ERR
1429	"VFS:Filesystem freeze failed\n");
1430	sb->s_writers.frozen = SB_UNFROZEN;
1431	sb_freeze_unlock(sb);
1432	wake_up(&sb->s_writers.wait_unfrozen);
1433	deactivate_locked_super(sb);
1434	return ret;
1435	}
1436	}
1437	/*
1438	* For debugging purposes so that fs can warn if it sees write activity
1439	* when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
1440	*/
1441	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1442	lockdep_sb_freeze_release(sb);
1443	up_write(&sb->s_umount);
1444	return 0;
1445	}
1446	EXPORT_SYMBOL(freeze_super);
1447
1448	/**
1449	* thaw_super -- unlock filesystem
1450	* @sb: the super to thaw
1451	*
1452	* Unlocks the filesystem and marks it writeable again after freeze_super().
1453	*/
1454	int thaw_super(struct super_block *sb)
1455	{
1456	int error;
1457
1458	down_write(&sb->s_umount);
1459	if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
1460	up_write(&sb->s_umount);
1461	return -EINVAL;
1462	}
1463
1464	if (sb->s_flags & MS_RDONLY) {
1465	sb->s_writers.frozen = SB_UNFROZEN;
1466	goto out;
1467	}
1468
1469	lockdep_sb_freeze_acquire(sb);
1470
1471	if (sb->s_op->unfreeze_fs) {
1472	error = sb->s_op->unfreeze_fs(sb);
1473	if (error) {
1474	printk(KERN_ERR
1475	"VFS:Filesystem thaw failed\n");
1476	lockdep_sb_freeze_release(sb);
1477	up_write(&sb->s_umount);
1478	return error;
1479	}
1480	}
1481
1482	sb->s_writers.frozen = SB_UNFROZEN;
1483	sb_freeze_unlock(sb);
1484	out:
1485	wake_up(&sb->s_writers.wait_unfrozen);
1486	deactivate_locked_super(sb);
1487	return 0;
1488	}
1489	EXPORT_SYMBOL(thaw_super);
1490