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Root/fs/super.c

1	/*
2	* linux/fs/super.c
3	*
4	* Copyright (C) 1991, 1992 Linus Torvalds
5	*
6	* super.c contains code to handle: - mount structures
7	* - super-block tables
8	* - filesystem drivers list
9	* - mount system call
10	* - umount system call
11	* - ustat system call
12	*
13	* GK 2/5/95 - Changed to support mounting the root fs via NFS
14	*
15	* Added kerneld support: Jacques Gelinas and Bjorn Ekwall
16	* Added change_root: Werner Almesberger & Hans Lermen, Feb '96
17	* Added options to /proc/mounts:
18	* Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
19	* Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
20	* Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
21	*/
22
23	#include <linux/export.h>
24	#include <linux/slab.h>
25	#include <linux/acct.h>
26	#include <linux/blkdev.h>
27	#include <linux/mount.h>
28	#include <linux/security.h>
29	#include <linux/writeback.h> /* for the emergency remount stuff */
30	#include <linux/idr.h>
31	#include <linux/mutex.h>
32	#include <linux/backing-dev.h>
33	#include <linux/rculist_bl.h>
34	#include <linux/cleancache.h>
35	#include <linux/fsnotify.h>
36	#include <linux/lockdep.h>
37	#include "internal.h"
38
39
40	LIST_HEAD(super_blocks);
41	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 int prune_super(struct shrinker shrink, struct shrink_control sc)
57	{
58	struct super_block *sb;
59	int fs_objects = 0;
60	int total_objects;
61
62	sb = container_of(shrink, struct super_block, s_shrink);
63
64	/*
65	* Deadlock avoidance. We may hold various FS locks, and we don't want
66	* to recurse into the FS that called us in clear_inode() and friends..
67	*/
68	if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
69	return -1;
70
71	if (!grab_super_passive(sb))
72	return -1;
73
74	if (sb->s_op && sb->s_op->nr_cached_objects)
75	fs_objects = sb->s_op->nr_cached_objects(sb);
76
77	total_objects = sb->s_nr_dentry_unused +
78	sb->s_nr_inodes_unused + fs_objects + 1;
79
80	if (sc->nr_to_scan) {
81	int dentries;
82	int inodes;
83
84	/* proportion the scan between the caches */
85	dentries = (sc->nr_to_scan * sb->s_nr_dentry_unused) /
86	total_objects;
87	inodes = (sc->nr_to_scan * sb->s_nr_inodes_unused) /
88	total_objects;
89	if (fs_objects)
90	fs_objects = (sc->nr_to_scan * fs_objects) /
91	total_objects;
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	prune_dcache_sb(sb, dentries);
97	prune_icache_sb(sb, inodes);
98
99	if (fs_objects && sb->s_op->free_cached_objects) {
100	sb->s_op->free_cached_objects(sb, fs_objects);
101	fs_objects = sb->s_op->nr_cached_objects(sb);
102	}
103	total_objects = sb->s_nr_dentry_unused +
104	sb->s_nr_inodes_unused + fs_objects;
105	}
106
107	total_objects = (total_objects / 100) * sysctl_vfs_cache_pressure;
108	drop_super(sb);
109	return total_objects;
110	}
111
112	static int init_sb_writers(struct super_block s, struct file_system_type type)
113	{
114	int err;
115	int i;
116
117	for (i = 0; i < SB_FREEZE_LEVELS; i++) {
118	err = percpu_counter_init(&s->s_writers.counter[i], 0);
119	if (err < 0)
120	goto err_out;
121	lockdep_init_map(&s->s_writers.lock_map[i], sb_writers_name[i],
122	&type->s_writers_key[i], 0);
123	}
124	init_waitqueue_head(&s->s_writers.wait);
125	init_waitqueue_head(&s->s_writers.wait_unfrozen);
126	return 0;
127	err_out:
128	while (--i >= 0)
129	percpu_counter_destroy(&s->s_writers.counter[i]);
130	return err;
131	}
132
133	static void destroy_sb_writers(struct super_block *s)
134	{
135	int i;
136
137	for (i = 0; i < SB_FREEZE_LEVELS; i++)
138	percpu_counter_destroy(&s->s_writers.counter[i]);
139	}
140
141	/**
142	* alloc_super - create new superblock
143	* @type: filesystem type superblock should belong to
144	* @flags: the mount flags
145	*
146	* Allocates and initializes a new &struct super_block. alloc_super()
147	* returns a pointer new superblock or %NULL if allocation had failed.
148	*/
149	static struct super_block alloc_super(struct file_system_type type, int flags)
150	{
151	struct super_block *s = kzalloc(sizeof(struct super_block), GFP_USER);
152	static const struct super_operations default_op;
153
154	if (s) {
155	if (security_sb_alloc(s)) {
156	/*
157	* We cannot call security_sb_free() without
158	* security_sb_alloc() succeeding. So bail out manually
159	*/
160	kfree(s);
161	s = NULL;
162	goto out;
163	}
164	#ifdef CONFIG_SMP
165	s->s_files = alloc_percpu(struct list_head);
166	if (!s->s_files)
167	goto err_out;
168	else {
169	int i;
170
171	for_each_possible_cpu(i)
172	INIT_LIST_HEAD(per_cpu_ptr(s->s_files, i));
173	}
174	#else
175	INIT_LIST_HEAD(&s->s_files);
176	#endif
177	if (init_sb_writers(s, type))
178	goto err_out;
179	s->s_flags = flags;
180	s->s_bdi = &default_backing_dev_info;
181	INIT_HLIST_NODE(&s->s_instances);
182	INIT_HLIST_BL_HEAD(&s->s_anon);
183	INIT_LIST_HEAD(&s->s_inodes);
184	INIT_LIST_HEAD(&s->s_dentry_lru);
185	INIT_LIST_HEAD(&s->s_inode_lru);
186	spin_lock_init(&s->s_inode_lru_lock);
187	INIT_LIST_HEAD(&s->s_mounts);
188	init_rwsem(&s->s_umount);
189	mutex_init(&s->s_lock);
190	lockdep_set_class(&s->s_umount, &type->s_umount_key);
191	/*
192	* The locking rules for s_lock are up to the
193	* filesystem. For example ext3fs has different
194	* lock ordering than usbfs:
195	*/
196	lockdep_set_class(&s->s_lock, &type->s_lock_key);
197	/*
198	* sget() can have s_umount recursion.
199	*
200	* When it cannot find a suitable sb, it allocates a new
201	* one (this one), and tries again to find a suitable old
202	* one.
203	*
204	* In case that succeeds, it will acquire the s_umount
205	* lock of the old one. Since these are clearly distrinct
206	* locks, and this object isn't exposed yet, there's no
207	* risk of deadlocks.
208	*
209	* Annotate this by putting this lock in a different
210	* subclass.
211	*/
212	down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
213	s->s_count = 1;
214	atomic_set(&s->s_active, 1);
215	mutex_init(&s->s_vfs_rename_mutex);
216	lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
217	mutex_init(&s->s_dquot.dqio_mutex);
218	mutex_init(&s->s_dquot.dqonoff_mutex);
219	init_rwsem(&s->s_dquot.dqptr_sem);
220	s->s_maxbytes = MAX_NON_LFS;
221	s->s_op = &default_op;
222	s->s_time_gran = 1000000000;
223	s->cleancache_poolid = -1;
224
225	s->s_shrink.seeks = DEFAULT_SEEKS;
226	s->s_shrink.shrink = prune_super;
227	s->s_shrink.batch = 1024;
228	}
229	out:
230	return s;
231	err_out:
232	security_sb_free(s);
233	#ifdef CONFIG_SMP
234	if (s->s_files)
235	free_percpu(s->s_files);
236	#endif
237	destroy_sb_writers(s);
238	kfree(s);
239	s = NULL;
240	goto out;
241	}
242
243	/**
244	* destroy_super - frees a superblock
245	* @s: superblock to free
246	*
247	* Frees a superblock.
248	*/
249	static inline void destroy_super(struct super_block *s)
250	{
251	#ifdef CONFIG_SMP
252	free_percpu(s->s_files);
253	#endif
254	destroy_sb_writers(s);
255	security_sb_free(s);
256	WARN_ON(!list_empty(&s->s_mounts));
257	kfree(s->s_subtype);
258	kfree(s->s_options);
259	kfree(s);
260	}
261
262	/* Superblock refcounting */
263
264	/*
265	* Drop a superblock's refcount. The caller must hold sb_lock.
266	*/
267	static void __put_super(struct super_block *sb)
268	{
269	if (!--sb->s_count) {
270	list_del_init(&sb->s_list);
271	destroy_super(sb);
272	}
273	}
274
275	/**
276	* put_super - drop a temporary reference to superblock
277	* @sb: superblock in question
278	*
279	* Drops a temporary reference, frees superblock if there's no
280	* references left.
281	*/
282	static void put_super(struct super_block *sb)
283	{
284	spin_lock(&sb_lock);
285	__put_super(sb);
286	spin_unlock(&sb_lock);
287	}
288
289
290	/**
291	* deactivate_locked_super - drop an active reference to superblock
292	* @s: superblock to deactivate
293	*
294	* Drops an active reference to superblock, converting it into a temprory
295	* one if there is no other active references left. In that case we
296	* tell fs driver to shut it down and drop the temporary reference we
297	* had just acquired.
298	*
299	* Caller holds exclusive lock on superblock; that lock is released.
300	*/
301	void deactivate_locked_super(struct super_block *s)
302	{
303	struct file_system_type *fs = s->s_type;
304	if (atomic_dec_and_test(&s->s_active)) {
305	cleancache_invalidate_fs(s);
306	fs->kill_sb(s);
307
308	/* caches are now gone, we can safely kill the shrinker now */
309	unregister_shrinker(&s->s_shrink);
310
311	/*
312	* We need to call rcu_barrier so all the delayed rcu free
313	* inodes are flushed before we release the fs module.
314	*/
315	rcu_barrier();
316	put_filesystem(fs);
317	put_super(s);
318	} else {
319	up_write(&s->s_umount);
320	}
321	}
322
323	EXPORT_SYMBOL(deactivate_locked_super);
324
325	/**
326	* deactivate_super - drop an active reference to superblock
327	* @s: superblock to deactivate
328	*
329	* Variant of deactivate_locked_super(), except that superblock is not
330	* locked by caller. If we are going to drop the final active reference,
331	* lock will be acquired prior to that.
332	*/
333	void deactivate_super(struct super_block *s)
334	{
335	if (!atomic_add_unless(&s->s_active, -1, 1)) {
336	down_write(&s->s_umount);
337	deactivate_locked_super(s);
338	}
339	}
340
341	EXPORT_SYMBOL(deactivate_super);
342
343	/**
344	* grab_super - acquire an active reference
345	* @s: reference we are trying to make active
346	*
347	* Tries to acquire an active reference. grab_super() is used when we
348	* had just found a superblock in super_blocks or fs_type->fs_supers
349	* and want to turn it into a full-blown active reference. grab_super()
350	* is called with sb_lock held and drops it. Returns 1 in case of
351	* success, 0 if we had failed (superblock contents was already dead or
352	* dying when grab_super() had been called).
353	*/
354	static int grab_super(struct super_block *s) __releases(sb_lock)
355	{
356	if (atomic_inc_not_zero(&s->s_active)) {
357	spin_unlock(&sb_lock);
358	return 1;
359	}
360	/* it's going away */
361	s->s_count++;
362	spin_unlock(&sb_lock);
363	/* wait for it to die */
364	down_write(&s->s_umount);
365	up_write(&s->s_umount);
366	put_super(s);
367	return 0;
368	}
369
370	/*
371	* grab_super_passive - acquire a passive reference
372	* @sb: reference we are trying to grab
373	*
374	* Tries to acquire a passive reference. This is used in places where we
375	* cannot take an active reference but we need to ensure that the
376	* superblock does not go away while we are working on it. It returns
377	* false if a reference was not gained, and returns true with the s_umount
378	* lock held in read mode if a reference is gained. On successful return,
379	* the caller must drop the s_umount lock and the passive reference when
380	* done.
381	*/
382	bool grab_super_passive(struct super_block *sb)
383	{
384	spin_lock(&sb_lock);
385	if (hlist_unhashed(&sb->s_instances)) {
386	spin_unlock(&sb_lock);
387	return false;
388	}
389
390	sb->s_count++;
391	spin_unlock(&sb_lock);
392
393	if (down_read_trylock(&sb->s_umount)) {
394	if (sb->s_root && (sb->s_flags & MS_BORN))
395	return true;
396	up_read(&sb->s_umount);
397	}
398
399	put_super(sb);
400	return false;
401	}
402
403	/*
404	* Superblock locking. We really ought to get rid of these two.
405	*/
406	void lock_super(struct super_block * sb)
407	{
408	mutex_lock(&sb->s_lock);
409	}
410
411	void unlock_super(struct super_block * sb)
412	{
413	mutex_unlock(&sb->s_lock);
414	}
415
416	EXPORT_SYMBOL(lock_super);
417	EXPORT_SYMBOL(unlock_super);
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 &= ~MS_ACTIVE;
441
442	fsnotify_unmount_inodes(&sb->s_inodes);
443
444	evict_inodes(sb);
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 - 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	* @data: argument to each of them
471	*/
472	struct super_block sget(struct file_system_type type,
473	int (test)(struct super_block ,void *),
474	int (set)(struct super_block ,void *),
475	int flags,
476	void *data)
477	{
478	struct super_block *s = NULL;
479	struct hlist_node *node;
480	struct super_block *old;
481	int err;
482
483	retry:
484	spin_lock(&sb_lock);
485	if (test) {
486	hlist_for_each_entry(old, node, &type->fs_supers, s_instances) {
487	if (!test(old, data))
488	continue;
489	if (!grab_super(old))
490	goto retry;
491	if (s) {
492	up_write(&s->s_umount);
493	destroy_super(s);
494	s = NULL;
495	}
496	down_write(&old->s_umount);
497	if (unlikely(!(old->s_flags & MS_BORN))) {
498	deactivate_locked_super(old);
499	goto retry;
500	}
501	return old;
502	}
503	}
504	if (!s) {
505	spin_unlock(&sb_lock);
506	s = alloc_super(type, flags);
507	if (!s)
508	return ERR_PTR(-ENOMEM);
509	goto retry;
510	}
511
512	err = set(s, data);
513	if (err) {
514	spin_unlock(&sb_lock);
515	up_write(&s->s_umount);
516	destroy_super(s);
517	return ERR_PTR(err);
518	}
519	s->s_type = type;
520	strlcpy(s->s_id, type->name, sizeof(s->s_id));
521	list_add_tail(&s->s_list, &super_blocks);
522	hlist_add_head(&s->s_instances, &type->fs_supers);
523	spin_unlock(&sb_lock);
524	get_filesystem(type);
525	register_shrinker(&s->s_shrink);
526	return s;
527	}
528
529	EXPORT_SYMBOL(sget);
530
531	void drop_super(struct super_block *sb)
532	{
533	up_read(&sb->s_umount);
534	put_super(sb);
535	}
536
537	EXPORT_SYMBOL(drop_super);
538
539	/**
540	* iterate_supers - call function for all active superblocks
541	* @f: function to call
542	* @arg: argument to pass to it
543	*
544	* Scans the superblock list and calls given function, passing it
545	* locked superblock and given argument.
546	*/
547	void iterate_supers(void (f)(struct super_block , void ), void arg)
548	{
549	struct super_block sb, p = NULL;
550
551	spin_lock(&sb_lock);
552	list_for_each_entry(sb, &super_blocks, s_list) {
553	if (hlist_unhashed(&sb->s_instances))
554	continue;
555	sb->s_count++;
556	spin_unlock(&sb_lock);
557
558	down_read(&sb->s_umount);
559	if (sb->s_root && (sb->s_flags & MS_BORN))
560	f(sb, arg);
561	up_read(&sb->s_umount);
562
563	spin_lock(&sb_lock);
564	if (p)
565	__put_super(p);
566	p = sb;
567	}
568	if (p)
569	__put_super(p);
570	spin_unlock(&sb_lock);
571	}
572
573	/**
574	* iterate_supers_type - call function for superblocks of given type
575	* @type: fs type
576	* @f: function to call
577	* @arg: argument to pass to it
578	*
579	* Scans the superblock list and calls given function, passing it
580	* locked superblock and given argument.
581	*/
582	void iterate_supers_type(struct file_system_type *type,
583	void (f)(struct super_block , void ), void arg)
584	{
585	struct super_block sb, p = NULL;
586	struct hlist_node *node;
587
588	spin_lock(&sb_lock);
589	hlist_for_each_entry(sb, node, &type->fs_supers, s_instances) {
590	sb->s_count++;
591	spin_unlock(&sb_lock);
592
593	down_read(&sb->s_umount);
594	if (sb->s_root && (sb->s_flags & MS_BORN))
595	f(sb, arg);
596	up_read(&sb->s_umount);
597
598	spin_lock(&sb_lock);
599	if (p)
600	__put_super(p);
601	p = sb;
602	}
603	if (p)
604	__put_super(p);
605	spin_unlock(&sb_lock);
606	}
607
608	EXPORT_SYMBOL(iterate_supers_type);
609
610	/**
611	* get_super - get the superblock of a device
612	* @bdev: device to get the superblock for
613	*
614	* Scans the superblock list and finds the superblock of the file system
615	* mounted on the device given. %NULL is returned if no match is found.
616	*/
617
618	struct super_block get_super(struct block_device bdev)
619	{
620	struct super_block *sb;
621
622	if (!bdev)
623	return NULL;
624
625	spin_lock(&sb_lock);
626	rescan:
627	list_for_each_entry(sb, &super_blocks, s_list) {
628	if (hlist_unhashed(&sb->s_instances))
629	continue;
630	if (sb->s_bdev == bdev) {
631	sb->s_count++;
632	spin_unlock(&sb_lock);
633	down_read(&sb->s_umount);
634	/* still alive? */
635	if (sb->s_root && (sb->s_flags & MS_BORN))
636	return sb;
637	up_read(&sb->s_umount);
638	/* nope, got unmounted */
639	spin_lock(&sb_lock);
640	__put_super(sb);
641	goto rescan;
642	}
643	}
644	spin_unlock(&sb_lock);
645	return NULL;
646	}
647
648	EXPORT_SYMBOL(get_super);
649
650	/**
651	* get_super_thawed - get thawed superblock of a device
652	* @bdev: device to get the superblock for
653	*
654	* Scans the superblock list and finds the superblock of the file system
655	* mounted on the device. The superblock is returned once it is thawed
656	* (or immediately if it was not frozen). %NULL is returned if no match
657	* is found.
658	*/
659	struct super_block get_super_thawed(struct block_device bdev)
660	{
661	while (1) {
662	struct super_block *s = get_super(bdev);
663	if (!s \|\| s->s_writers.frozen == SB_UNFROZEN)
664	return s;
665	up_read(&s->s_umount);
666	wait_event(s->s_writers.wait_unfrozen,
667	s->s_writers.frozen == SB_UNFROZEN);
668	put_super(s);
669	}
670	}
671	EXPORT_SYMBOL(get_super_thawed);
672
673	/**
674	* get_active_super - get an active reference to the superblock of a device
675	* @bdev: device to get the superblock for
676	*
677	* Scans the superblock list and finds the superblock of the file system
678	* mounted on the device given. Returns the superblock with an active
679	* reference or %NULL if none was found.
680	*/
681	struct super_block get_active_super(struct block_device bdev)
682	{
683	struct super_block *sb;
684
685	if (!bdev)
686	return NULL;
687
688	restart:
689	spin_lock(&sb_lock);
690	list_for_each_entry(sb, &super_blocks, s_list) {
691	if (hlist_unhashed(&sb->s_instances))
692	continue;
693	if (sb->s_bdev == bdev) {
694	if (grab_super(sb)) /* drops sb_lock */
695	return sb;
696	else
697	goto restart;
698	}
699	}
700	spin_unlock(&sb_lock);
701	return NULL;
702	}
703
704	struct super_block *user_get_super(dev_t dev)
705	{
706	struct super_block *sb;
707
708	spin_lock(&sb_lock);
709	rescan:
710	list_for_each_entry(sb, &super_blocks, s_list) {
711	if (hlist_unhashed(&sb->s_instances))
712	continue;
713	if (sb->s_dev == dev) {
714	sb->s_count++;
715	spin_unlock(&sb_lock);
716	down_read(&sb->s_umount);
717	/* still alive? */
718	if (sb->s_root && (sb->s_flags & MS_BORN))
719	return sb;
720	up_read(&sb->s_umount);
721	/* nope, got unmounted */
722	spin_lock(&sb_lock);
723	__put_super(sb);
724	goto rescan;
725	}
726	}
727	spin_unlock(&sb_lock);
728	return NULL;
729	}
730
731	/**
732	* do_remount_sb - asks filesystem to change mount options.
733	* @sb: superblock in question
734	* @flags: numeric part of options
735	* @data: the rest of options
736	* @force: whether or not to force the change
737	*
738	* Alters the mount options of a mounted file system.
739	*/
740	int do_remount_sb(struct super_block sb, int flags, void data, int force)
741	{
742	int retval;
743	int remount_ro;
744
745	if (sb->s_writers.frozen != SB_UNFROZEN)
746	return -EBUSY;
747
748	#ifdef CONFIG_BLOCK
749	if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
750	return -EACCES;
751	#endif
752
753	if (flags & MS_RDONLY)
754	acct_auto_close(sb);
755	shrink_dcache_sb(sb);
756	sync_filesystem(sb);
757
758	remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
759
760	/* If we are remounting RDONLY and current sb is read/write,
761	make sure there are no rw files opened */
762	if (remount_ro) {
763	if (force) {
764	mark_files_ro(sb);
765	} else {
766	retval = sb_prepare_remount_readonly(sb);
767	if (retval)
768	return retval;
769	}
770	}
771
772	if (sb->s_op->remount_fs) {
773	retval = sb->s_op->remount_fs(sb, &flags, data);
774	if (retval) {
775	if (!force)
776	goto cancel_readonly;
777	/* If forced remount, go ahead despite any errors */
778	WARN(1, "forced remount of a %s fs returned %i\n",
779	sb->s_type->name, retval);
780	}
781	}
782	sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) \| (flags & MS_RMT_MASK);
783	/* Needs to be ordered wrt mnt_is_readonly() */
784	smp_wmb();
785	sb->s_readonly_remount = 0;
786
787	/*
788	* Some filesystems modify their metadata via some other path than the
789	* bdev buffer cache (eg. use a private mapping, or directories in
790	* pagecache, etc). Also file data modifications go via their own
791	* mappings. So If we try to mount readonly then copy the filesystem
792	* from bdev, we could get stale data, so invalidate it to give a best
793	* effort at coherency.
794	*/
795	if (remount_ro && sb->s_bdev)
796	invalidate_bdev(sb->s_bdev);
797	return 0;
798
799	cancel_readonly:
800	sb->s_readonly_remount = 0;
801	return retval;
802	}
803
804	static void do_emergency_remount(struct work_struct *work)
805	{
806	struct super_block sb, p = NULL;
807
808	spin_lock(&sb_lock);
809	list_for_each_entry(sb, &super_blocks, s_list) {
810	if (hlist_unhashed(&sb->s_instances))
811	continue;
812	sb->s_count++;
813	spin_unlock(&sb_lock);
814	down_write(&sb->s_umount);
815	if (sb->s_root && sb->s_bdev && (sb->s_flags & MS_BORN) &&
816	!(sb->s_flags & MS_RDONLY)) {
817	/*
818	* What lock protects sb->s_flags??
819	*/
820	do_remount_sb(sb, MS_RDONLY, NULL, 1);
821	}
822	up_write(&sb->s_umount);
823	spin_lock(&sb_lock);
824	if (p)
825	__put_super(p);
826	p = sb;
827	}
828	if (p)
829	__put_super(p);
830	spin_unlock(&sb_lock);
831	kfree(work);
832	printk("Emergency Remount complete\n");
833	}
834
835	void emergency_remount(void)
836	{
837	struct work_struct *work;
838
839	work = kmalloc(sizeof(*work), GFP_ATOMIC);
840	if (work) {
841	INIT_WORK(work, do_emergency_remount);
842	schedule_work(work);
843	}
844	}
845
846	/*
847	* Unnamed block devices are dummy devices used by virtual
848	* filesystems which don't use real block-devices. -- jrs
849	*/
850
851	static DEFINE_IDA(unnamed_dev_ida);
852	static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
853	static int unnamed_dev_start = 0; /* don't bother trying below it */
854
855	int get_anon_bdev(dev_t *p)
856	{
857	int dev;
858	int error;
859
860	retry:
861	if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
862	return -ENOMEM;
863	spin_lock(&unnamed_dev_lock);
864	error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
865	if (!error)
866	unnamed_dev_start = dev + 1;
867	spin_unlock(&unnamed_dev_lock);
868	if (error == -EAGAIN)
869	/* We raced and lost with another CPU. */
870	goto retry;
871	else if (error)
872	return -EAGAIN;
873
874	if ((dev & MAX_ID_MASK) == (1 << MINORBITS)) {
875	spin_lock(&unnamed_dev_lock);
876	ida_remove(&unnamed_dev_ida, dev);
877	if (unnamed_dev_start > dev)
878	unnamed_dev_start = dev;
879	spin_unlock(&unnamed_dev_lock);
880	return -EMFILE;
881	}
882	*p = MKDEV(0, dev & MINORMASK);
883	return 0;
884	}
885	EXPORT_SYMBOL(get_anon_bdev);
886
887	void free_anon_bdev(dev_t dev)
888	{
889	int slot = MINOR(dev);
890	spin_lock(&unnamed_dev_lock);
891	ida_remove(&unnamed_dev_ida, slot);
892	if (slot < unnamed_dev_start)
893	unnamed_dev_start = slot;
894	spin_unlock(&unnamed_dev_lock);
895	}
896	EXPORT_SYMBOL(free_anon_bdev);
897
898	int set_anon_super(struct super_block s, void data)
899	{
900	int error = get_anon_bdev(&s->s_dev);
901	if (!error)
902	s->s_bdi = &noop_backing_dev_info;
903	return error;
904	}
905
906	EXPORT_SYMBOL(set_anon_super);
907
908	void kill_anon_super(struct super_block *sb)
909	{
910	dev_t dev = sb->s_dev;
911	generic_shutdown_super(sb);
912	free_anon_bdev(dev);
913	}
914
915	EXPORT_SYMBOL(kill_anon_super);
916
917	void kill_litter_super(struct super_block *sb)
918	{
919	if (sb->s_root)
920	d_genocide(sb->s_root);
921	kill_anon_super(sb);
922	}
923
924	EXPORT_SYMBOL(kill_litter_super);
925
926	static int ns_test_super(struct super_block sb, void data)
927	{
928	return sb->s_fs_info == data;
929	}
930
931	static int ns_set_super(struct super_block sb, void data)
932	{
933	sb->s_fs_info = data;
934	return set_anon_super(sb, NULL);
935	}
936
937	struct dentry mount_ns(struct file_system_type fs_type, int flags,
938	void data, int (fill_super)(struct super_block , void , int))
939	{
940	struct super_block *sb;
941
942	sb = sget(fs_type, ns_test_super, ns_set_super, flags, data);
943	if (IS_ERR(sb))
944	return ERR_CAST(sb);
945
946	if (!sb->s_root) {
947	int err;
948	err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
949	if (err) {
950	deactivate_locked_super(sb);
951	return ERR_PTR(err);
952	}
953
954	sb->s_flags \|= MS_ACTIVE;
955	}
956
957	return dget(sb->s_root);
958	}
959
960	EXPORT_SYMBOL(mount_ns);
961
962	#ifdef CONFIG_BLOCK
963	static int set_bdev_super(struct super_block s, void data)
964	{
965	s->s_bdev = data;
966	s->s_dev = s->s_bdev->bd_dev;
967
968	/*
969	* We set the bdi here to the queue backing, file systems can
970	* overwrite this in ->fill_super()
971	*/
972	s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
973	return 0;
974	}
975
976	static int test_bdev_super(struct super_block s, void data)
977	{
978	return (void *)s->s_bdev == data;
979	}
980
981	struct dentry mount_bdev(struct file_system_type fs_type,
982	int flags, const char dev_name, void data,
983	int (fill_super)(struct super_block , void *, int))
984	{
985	struct block_device *bdev;
986	struct super_block *s;
987	fmode_t mode = FMODE_READ \| FMODE_EXCL;
988	int error = 0;
989
990	if (!(flags & MS_RDONLY))
991	mode \|= FMODE_WRITE;
992
993	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
994	if (IS_ERR(bdev))
995	return ERR_CAST(bdev);
996
997	/*
998	* once the super is inserted into the list by sget, s_umount
999	* will protect the lockfs code from trying to start a snapshot
1000	* while we are mounting
1001	*/
1002	mutex_lock(&bdev->bd_fsfreeze_mutex);
1003	if (bdev->bd_fsfreeze_count > 0) {
1004	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1005	error = -EBUSY;
1006	goto error_bdev;
1007	}
1008	s = sget(fs_type, test_bdev_super, set_bdev_super, flags \| MS_NOSEC,
1009	bdev);
1010	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1011	if (IS_ERR(s))
1012	goto error_s;
1013
1014	if (s->s_root) {
1015	if ((flags ^ s->s_flags) & MS_RDONLY) {
1016	deactivate_locked_super(s);
1017	error = -EBUSY;
1018	goto error_bdev;
1019	}
1020
1021	/*
1022	* s_umount nests inside bd_mutex during
1023	* __invalidate_device(). blkdev_put() acquires
1024	* bd_mutex and can't be called under s_umount. Drop
1025	* s_umount temporarily. This is safe as we're
1026	* holding an active reference.
1027	*/
1028	up_write(&s->s_umount);
1029	blkdev_put(bdev, mode);
1030	down_write(&s->s_umount);
1031	} else {
1032	char b[BDEVNAME_SIZE];
1033
1034	s->s_mode = mode;
1035	strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
1036	sb_set_blocksize(s, block_size(bdev));
1037	error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1038	if (error) {
1039	deactivate_locked_super(s);
1040	goto error;
1041	}
1042
1043	s->s_flags \|= MS_ACTIVE;
1044	bdev->bd_super = s;
1045	}
1046
1047	return dget(s->s_root);
1048
1049	error_s:
1050	error = PTR_ERR(s);
1051	error_bdev:
1052	blkdev_put(bdev, mode);
1053	error:
1054	return ERR_PTR(error);
1055	}
1056	EXPORT_SYMBOL(mount_bdev);
1057
1058	void kill_block_super(struct super_block *sb)
1059	{
1060	struct block_device *bdev = sb->s_bdev;
1061	fmode_t mode = sb->s_mode;
1062
1063	bdev->bd_super = NULL;
1064	generic_shutdown_super(sb);
1065	sync_blockdev(bdev);
1066	WARN_ON_ONCE(!(mode & FMODE_EXCL));
1067	blkdev_put(bdev, mode \| FMODE_EXCL);
1068	}
1069
1070	EXPORT_SYMBOL(kill_block_super);
1071	#endif
1072
1073	struct dentry mount_nodev(struct file_system_type fs_type,
1074	int flags, void *data,
1075	int (fill_super)(struct super_block , void *, int))
1076	{
1077	int error;
1078	struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1079
1080	if (IS_ERR(s))
1081	return ERR_CAST(s);
1082
1083	error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1084	if (error) {
1085	deactivate_locked_super(s);
1086	return ERR_PTR(error);
1087	}
1088	s->s_flags \|= MS_ACTIVE;
1089	return dget(s->s_root);
1090	}
1091	EXPORT_SYMBOL(mount_nodev);
1092
1093	static int compare_single(struct super_block s, void p)
1094	{
1095	return 1;
1096	}
1097
1098	struct dentry mount_single(struct file_system_type fs_type,
1099	int flags, void *data,
1100	int (fill_super)(struct super_block , void *, int))
1101	{
1102	struct super_block *s;
1103	int error;
1104
1105	s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1106	if (IS_ERR(s))
1107	return ERR_CAST(s);
1108	if (!s->s_root) {
1109	error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1110	if (error) {
1111	deactivate_locked_super(s);
1112	return ERR_PTR(error);
1113	}
1114	s->s_flags \|= MS_ACTIVE;
1115	} else {
1116	do_remount_sb(s, flags, data, 0);
1117	}
1118	return dget(s->s_root);
1119	}
1120	EXPORT_SYMBOL(mount_single);
1121
1122	struct dentry *
1123	mount_fs(struct file_system_type type, int flags, const char name, void *data)
1124	{
1125	struct dentry *root;
1126	struct super_block *sb;
1127	char *secdata = NULL;
1128	int error = -ENOMEM;
1129
1130	if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
1131	secdata = alloc_secdata();
1132	if (!secdata)
1133	goto out;
1134
1135	error = security_sb_copy_data(data, secdata);
1136	if (error)
1137	goto out_free_secdata;
1138	}
1139
1140	root = type->mount(type, flags, name, data);
1141	if (IS_ERR(root)) {
1142	error = PTR_ERR(root);
1143	goto out_free_secdata;
1144	}
1145	sb = root->d_sb;
1146	BUG_ON(!sb);
1147	WARN_ON(!sb->s_bdi);
1148	WARN_ON(sb->s_bdi == &default_backing_dev_info);
1149	sb->s_flags \|= MS_BORN;
1150
1151	error = security_sb_kern_mount(sb, flags, secdata);
1152	if (error)
1153	goto out_sb;
1154
1155	/*
1156	* filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1157	* but s_maxbytes was an unsigned long long for many releases. Throw
1158	* this warning for a little while to try and catch filesystems that
1159	* violate this rule.
1160	*/
1161	WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1162	"negative value (%lld)\n", type->name, sb->s_maxbytes);
1163
1164	up_write(&sb->s_umount);
1165	free_secdata(secdata);
1166	return root;
1167	out_sb:
1168	dput(root);
1169	deactivate_locked_super(sb);
1170	out_free_secdata:
1171	free_secdata(secdata);
1172	out:
1173	return ERR_PTR(error);
1174	}
1175
1176	/*
1177	* This is an internal function, please use sb_end_{write,pagefault,intwrite}
1178	* instead.
1179	*/
1180	void __sb_end_write(struct super_block *sb, int level)
1181	{
1182	percpu_counter_dec(&sb->s_writers.counter[level-1]);
1183	/*
1184	* Make sure s_writers are updated before we wake up waiters in
1185	* freeze_super().
1186	*/
1187	smp_mb();
1188	if (waitqueue_active(&sb->s_writers.wait))
1189	wake_up(&sb->s_writers.wait);
1190	rwsem_release(&sb->s_writers.lock_map[level-1], 1, _RET_IP_);
1191	}
1192	EXPORT_SYMBOL(__sb_end_write);
1193
1194	#ifdef CONFIG_LOCKDEP
1195	/*
1196	* We want lockdep to tell us about possible deadlocks with freezing but
1197	* it's it bit tricky to properly instrument it. Getting a freeze protection
1198	* works as getting a read lock but there are subtle problems. XFS for example
1199	* gets freeze protection on internal level twice in some cases, which is OK
1200	* only because we already hold a freeze protection also on higher level. Due
1201	* to these cases we have to tell lockdep we are doing trylock when we
1202	* already hold a freeze protection for a higher freeze level.
1203	*/
1204	static void acquire_freeze_lock(struct super_block *sb, int level, bool trylock,
1205	unsigned long ip)
1206	{
1207	int i;
1208
1209	if (!trylock) {
1210	for (i = 0; i < level - 1; i++)
1211	if (lock_is_held(&sb->s_writers.lock_map[i])) {
1212	trylock = true;
1213	break;
1214	}
1215	}
1216	rwsem_acquire_read(&sb->s_writers.lock_map[level-1], 0, trylock, ip);
1217	}
1218	#endif
1219
1220	/*
1221	* This is an internal function, please use sb_start_{write,pagefault,intwrite}
1222	* instead.
1223	*/
1224	int __sb_start_write(struct super_block *sb, int level, bool wait)
1225	{
1226	retry:
1227	if (unlikely(sb->s_writers.frozen >= level)) {
1228	if (!wait)
1229	return 0;
1230	wait_event(sb->s_writers.wait_unfrozen,
1231	sb->s_writers.frozen < level);
1232	}
1233
1234	#ifdef CONFIG_LOCKDEP
1235	acquire_freeze_lock(sb, level, !wait, _RET_IP_);
1236	#endif
1237	percpu_counter_inc(&sb->s_writers.counter[level-1]);
1238	/*
1239	* Make sure counter is updated before we check for frozen.
1240	* freeze_super() first sets frozen and then checks the counter.
1241	*/
1242	smp_mb();
1243	if (unlikely(sb->s_writers.frozen >= level)) {
1244	__sb_end_write(sb, level);
1245	goto retry;
1246	}
1247	return 1;
1248	}
1249	EXPORT_SYMBOL(__sb_start_write);
1250
1251	/**
1252	* sb_wait_write - wait until all writers to given file system finish
1253	* @sb: the super for which we wait
1254	* @level: type of writers we wait for (normal vs page fault)
1255	*
1256	* This function waits until there are no writers of given type to given file
1257	* system. Caller of this function should make sure there can be no new writers
1258	* of type @level before calling this function. Otherwise this function can
1259	* livelock.
1260	*/
1261	static void sb_wait_write(struct super_block *sb, int level)
1262	{
1263	s64 writers;
1264
1265	/*
1266	* We just cycle-through lockdep here so that it does not complain
1267	* about returning with lock to userspace
1268	*/
1269	rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_);
1270	rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_);
1271
1272	do {
1273	DEFINE_WAIT(wait);
1274
1275	/*
1276	* We use a barrier in prepare_to_wait() to separate setting
1277	* of frozen and checking of the counter
1278	*/
1279	prepare_to_wait(&sb->s_writers.wait, &wait,
1280	TASK_UNINTERRUPTIBLE);
1281
1282	writers = percpu_counter_sum(&sb->s_writers.counter[level-1]);
1283	if (writers)
1284	schedule();
1285
1286	finish_wait(&sb->s_writers.wait, &wait);
1287	} while (writers);
1288	}
1289
1290	/**
1291	* freeze_super - lock the filesystem and force it into a consistent state
1292	* @sb: the super to lock
1293	*
1294	* Syncs the super to make sure the filesystem is consistent and calls the fs's
1295	* freeze_fs. Subsequent calls to this without first thawing the fs will return
1296	* -EBUSY.
1297	*
1298	* During this function, sb->s_writers.frozen goes through these values:
1299	*
1300	* SB_UNFROZEN: File system is normal, all writes progress as usual.
1301	*
1302	* SB_FREEZE_WRITE: The file system is in the process of being frozen. New
1303	* writes should be blocked, though page faults are still allowed. We wait for
1304	* all writes to complete and then proceed to the next stage.
1305	*
1306	* SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1307	* but internal fs threads can still modify the filesystem (although they
1308	* should not dirty new pages or inodes), writeback can run etc. After waiting
1309	* for all running page faults we sync the filesystem which will clean all
1310	* dirty pages and inodes (no new dirty pages or inodes can be created when
1311	* sync is running).
1312	*
1313	* SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1314	* modification are blocked (e.g. XFS preallocation truncation on inode
1315	* reclaim). This is usually implemented by blocking new transactions for
1316	* filesystems that have them and need this additional guard. After all
1317	* internal writers are finished we call ->freeze_fs() to finish filesystem
1318	* freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1319	* mostly auxiliary for filesystems to verify they do not modify frozen fs.
1320	*
1321	* sb->s_writers.frozen is protected by sb->s_umount.
1322	*/
1323	int freeze_super(struct super_block *sb)
1324	{
1325	int ret;
1326
1327	atomic_inc(&sb->s_active);
1328	down_write(&sb->s_umount);
1329	if (sb->s_writers.frozen != SB_UNFROZEN) {
1330	deactivate_locked_super(sb);
1331	return -EBUSY;
1332	}
1333
1334	if (!(sb->s_flags & MS_BORN)) {
1335	up_write(&sb->s_umount);
1336	return 0; /* sic - it's "nothing to do" */
1337	}
1338
1339	if (sb->s_flags & MS_RDONLY) {
1340	/* Nothing to do really... */
1341	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1342	up_write(&sb->s_umount);
1343	return 0;
1344	}
1345
1346	/* From now on, no new normal writers can start */
1347	sb->s_writers.frozen = SB_FREEZE_WRITE;
1348	smp_wmb();
1349
1350	/* Release s_umount to preserve sb_start_write -> s_umount ordering */
1351	up_write(&sb->s_umount);
1352
1353	sb_wait_write(sb, SB_FREEZE_WRITE);
1354
1355	/* Now we go and block page faults... */
1356	down_write(&sb->s_umount);
1357	sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1358	smp_wmb();
1359
1360	sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1361
1362	/* All writers are done so after syncing there won't be dirty data */
1363	sync_filesystem(sb);
1364
1365	/* Now wait for internal filesystem counter */
1366	sb->s_writers.frozen = SB_FREEZE_FS;
1367	smp_wmb();
1368	sb_wait_write(sb, SB_FREEZE_FS);
1369
1370	if (sb->s_op->freeze_fs) {
1371	ret = sb->s_op->freeze_fs(sb);
1372	if (ret) {
1373	printk(KERN_ERR
1374	"VFS:Filesystem freeze failed\n");
1375	sb->s_writers.frozen = SB_UNFROZEN;
1376	smp_wmb();
1377	wake_up(&sb->s_writers.wait_unfrozen);
1378	deactivate_locked_super(sb);
1379	return ret;
1380	}
1381	}
1382	/*
1383	* This is just for debugging purposes so that fs can warn if it
1384	* sees write activity when frozen is set to SB_FREEZE_COMPLETE.
1385	*/
1386	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1387	up_write(&sb->s_umount);
1388	return 0;
1389	}
1390	EXPORT_SYMBOL(freeze_super);
1391
1392	/**
1393	* thaw_super -- unlock filesystem
1394	* @sb: the super to thaw
1395	*
1396	* Unlocks the filesystem and marks it writeable again after freeze_super().
1397	*/
1398	int thaw_super(struct super_block *sb)
1399	{
1400	int error;
1401
1402	down_write(&sb->s_umount);
1403	if (sb->s_writers.frozen == SB_UNFROZEN) {
1404	up_write(&sb->s_umount);
1405	return -EINVAL;
1406	}
1407
1408	if (sb->s_flags & MS_RDONLY)
1409	goto out;
1410
1411	if (sb->s_op->unfreeze_fs) {
1412	error = sb->s_op->unfreeze_fs(sb);
1413	if (error) {
1414	printk(KERN_ERR
1415	"VFS:Filesystem thaw failed\n");
1416	up_write(&sb->s_umount);
1417	return error;
1418	}
1419	}
1420
1421	out:
1422	sb->s_writers.frozen = SB_UNFROZEN;
1423	smp_wmb();
1424	wake_up(&sb->s_writers.wait_unfrozen);
1425	deactivate_locked_super(sb);
1426
1427	return 0;
1428	}
1429	EXPORT_SYMBOL(thaw_super);
1430

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