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/fscrypt.h>
  36#include <linux/fsnotify.h>
  37#include <linux/lockdep.h>
  38#include <linux/user_namespace.h>
  39#include <linux/fs_context.h>
  40#include <uapi/linux/mount.h>
  41#include "internal.h"
  42
  43static int thaw_super_locked(struct super_block *sb);
  44
  45static LIST_HEAD(super_blocks);
  46static DEFINE_SPINLOCK(sb_lock);
  47
  48static char *sb_writers_name[SB_FREEZE_LEVELS] = {
  49	"sb_writers",
  50	"sb_pagefaults",
  51	"sb_internal",
  52};
  53
  54/*
  55 * One thing we have to be careful of with a per-sb shrinker is that we don't
  56 * drop the last active reference to the superblock from within the shrinker.
  57 * If that happens we could trigger unregistering the shrinker from within the
  58 * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
  59 * take a passive reference to the superblock to avoid this from occurring.
  60 */
  61static unsigned long super_cache_scan(struct shrinker *shrink,
  62				      struct shrink_control *sc)
  63{
  64	struct super_block *sb;
  65	long	fs_objects = 0;
  66	long	total_objects;
  67	long	freed = 0;
  68	long	dentries;
  69	long	inodes;
  70
  71	sb = container_of(shrink, struct super_block, s_shrink);
  72
  73	/*
  74	 * Deadlock avoidance.  We may hold various FS locks, and we don't want
  75	 * to recurse into the FS that called us in clear_inode() and friends..
  76	 */
  77	if (!(sc->gfp_mask & __GFP_FS))
  78		return SHRINK_STOP;
  79
  80	if (!trylock_super(sb))
  81		return SHRINK_STOP;
  82
  83	if (sb->s_op->nr_cached_objects)
  84		fs_objects = sb->s_op->nr_cached_objects(sb, sc);
  85
  86	inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
  87	dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc);
  88	total_objects = dentries + inodes + fs_objects + 1;
  89	if (!total_objects)
  90		total_objects = 1;
  91
  92	/* proportion the scan between the caches */
  93	dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);
  94	inodes = mult_frac(sc->nr_to_scan, inodes, total_objects);
  95	fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
  96
  97	/*
  98	 * prune the dcache first as the icache is pinned by it, then
  99	 * prune the icache, followed by the filesystem specific caches
 100	 *
 101	 * Ensure that we always scan at least one object - memcg kmem
 102	 * accounting uses this to fully empty the caches.
 103	 */
 104	sc->nr_to_scan = dentries + 1;
 105	freed = prune_dcache_sb(sb, sc);
 106	sc->nr_to_scan = inodes + 1;
 107	freed += prune_icache_sb(sb, sc);
 108
 109	if (fs_objects) {
 110		sc->nr_to_scan = fs_objects + 1;
 111		freed += sb->s_op->free_cached_objects(sb, sc);
 112	}
 113
 114	up_read(&sb->s_umount);
 115	return freed;
 116}
 117
 118static unsigned long super_cache_count(struct shrinker *shrink,
 119				       struct shrink_control *sc)
 120{
 121	struct super_block *sb;
 122	long	total_objects = 0;
 123
 124	sb = container_of(shrink, struct super_block, s_shrink);
 125
 126	/*
 127	 * We don't call trylock_super() here as it is a scalability bottleneck,
 128	 * so we're exposed to partial setup state. The shrinker rwsem does not
 129	 * protect filesystem operations backing list_lru_shrink_count() or
 130	 * s_op->nr_cached_objects(). Counts can change between
 131	 * super_cache_count and super_cache_scan, so we really don't need locks
 132	 * here.
 133	 *
 134	 * However, if we are currently mounting the superblock, the underlying
 135	 * filesystem might be in a state of partial construction and hence it
 136	 * is dangerous to access it.  trylock_super() uses a SB_BORN check to
 137	 * avoid this situation, so do the same here. The memory barrier is
 138	 * matched with the one in mount_fs() as we don't hold locks here.
 139	 */
 140	if (!(sb->s_flags & SB_BORN))
 141		return 0;
 142	smp_rmb();
 143
 144	if (sb->s_op && sb->s_op->nr_cached_objects)
 145		total_objects = sb->s_op->nr_cached_objects(sb, sc);
 146
 147	total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
 148	total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
 149
 150	if (!total_objects)
 151		return SHRINK_EMPTY;
 152
 153	total_objects = vfs_pressure_ratio(total_objects);
 154	return total_objects;
 155}
 156
 157static void destroy_super_work(struct work_struct *work)
 158{
 159	struct super_block *s = container_of(work, struct super_block,
 160							destroy_work);
 161	int i;
 162
 163	for (i = 0; i < SB_FREEZE_LEVELS; i++)
 164		percpu_free_rwsem(&s->s_writers.rw_sem[i]);
 165	kfree(s);
 166}
 167
 168static void destroy_super_rcu(struct rcu_head *head)
 169{
 170	struct super_block *s = container_of(head, struct super_block, rcu);
 171	INIT_WORK(&s->destroy_work, destroy_super_work);
 172	schedule_work(&s->destroy_work);
 173}
 174
 175/* Free a superblock that has never been seen by anyone */
 176static void destroy_unused_super(struct super_block *s)
 177{
 178	if (!s)
 179		return;
 180	up_write(&s->s_umount);
 181	list_lru_destroy(&s->s_dentry_lru);
 182	list_lru_destroy(&s->s_inode_lru);
 183	security_sb_free(s);
 184	put_user_ns(s->s_user_ns);
 185	kfree(s->s_subtype);
 186	free_prealloced_shrinker(&s->s_shrink);
 187	/* no delays needed */
 188	destroy_super_work(&s->destroy_work);
 189}
 190
 191/**
 192 *	alloc_super	-	create new superblock
 193 *	@type:	filesystem type superblock should belong to
 194 *	@flags: the mount flags
 195 *	@user_ns: User namespace for the super_block
 196 *
 197 *	Allocates and initializes a new &struct super_block.  alloc_super()
 198 *	returns a pointer new superblock or %NULL if allocation had failed.
 199 */
 200static struct super_block *alloc_super(struct file_system_type *type, int flags,
 201				       struct user_namespace *user_ns)
 202{
 203	struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
 204	static const struct super_operations default_op;
 205	int i;
 206
 207	if (!s)
 208		return NULL;
 209
 210	INIT_LIST_HEAD(&s->s_mounts);
 211	s->s_user_ns = get_user_ns(user_ns);
 212	init_rwsem(&s->s_umount);
 213	lockdep_set_class(&s->s_umount, &type->s_umount_key);
 214	/*
 215	 * sget() can have s_umount recursion.
 216	 *
 217	 * When it cannot find a suitable sb, it allocates a new
 218	 * one (this one), and tries again to find a suitable old
 219	 * one.
 220	 *
 221	 * In case that succeeds, it will acquire the s_umount
 222	 * lock of the old one. Since these are clearly distrinct
 223	 * locks, and this object isn't exposed yet, there's no
 224	 * risk of deadlocks.
 225	 *
 226	 * Annotate this by putting this lock in a different
 227	 * subclass.
 228	 */
 229	down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
 230
 231	if (security_sb_alloc(s))
 232		goto fail;
 233
 234	for (i = 0; i < SB_FREEZE_LEVELS; i++) {
 235		if (__percpu_init_rwsem(&s->s_writers.rw_sem[i],
 236					sb_writers_name[i],
 237					&type->s_writers_key[i]))
 238			goto fail;
 239	}
 240	init_waitqueue_head(&s->s_writers.wait_unfrozen);
 241	s->s_bdi = &noop_backing_dev_info;
 242	s->s_flags = flags;
 243	if (s->s_user_ns != &init_user_ns)
 244		s->s_iflags |= SB_I_NODEV;
 245	INIT_HLIST_NODE(&s->s_instances);
 246	INIT_HLIST_BL_HEAD(&s->s_roots);
 247	mutex_init(&s->s_sync_lock);
 248	INIT_LIST_HEAD(&s->s_inodes);
 249	spin_lock_init(&s->s_inode_list_lock);
 250	INIT_LIST_HEAD(&s->s_inodes_wb);
 251	spin_lock_init(&s->s_inode_wblist_lock);
 252
 253	s->s_count = 1;
 254	atomic_set(&s->s_active, 1);
 255	mutex_init(&s->s_vfs_rename_mutex);
 256	lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
 257	init_rwsem(&s->s_dquot.dqio_sem);
 258	s->s_maxbytes = MAX_NON_LFS;
 259	s->s_op = &default_op;
 260	s->s_time_gran = 1000000000;
 261	s->s_time_min = TIME64_MIN;
 262	s->s_time_max = TIME64_MAX;
 263	s->cleancache_poolid = CLEANCACHE_NO_POOL;
 264
 265	s->s_shrink.seeks = DEFAULT_SEEKS;
 266	s->s_shrink.scan_objects = super_cache_scan;
 267	s->s_shrink.count_objects = super_cache_count;
 268	s->s_shrink.batch = 1024;
 269	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
 270	if (prealloc_shrinker(&s->s_shrink))
 271		goto fail;
 272	if (list_lru_init_memcg(&s->s_dentry_lru, &s->s_shrink))
 273		goto fail;
 274	if (list_lru_init_memcg(&s->s_inode_lru, &s->s_shrink))
 275		goto fail;
 276	return s;
 277
 278fail:
 279	destroy_unused_super(s);
 280	return NULL;
 281}
 282
 283/* Superblock refcounting  */
 284
 285/*
 286 * Drop a superblock's refcount.  The caller must hold sb_lock.
 287 */
 288static void __put_super(struct super_block *s)
 289{
 290	if (!--s->s_count) {
 291		list_del_init(&s->s_list);
 292		WARN_ON(s->s_dentry_lru.node);
 293		WARN_ON(s->s_inode_lru.node);
 294		WARN_ON(!list_empty(&s->s_mounts));
 295		security_sb_free(s);
 296		fscrypt_sb_free(s);
 297		put_user_ns(s->s_user_ns);
 298		kfree(s->s_subtype);
 299		call_rcu(&s->rcu, destroy_super_rcu);
 300	}
 301}
 302
 303/**
 304 *	put_super	-	drop a temporary reference to superblock
 305 *	@sb: superblock in question
 306 *
 307 *	Drops a temporary reference, frees superblock if there's no
 308 *	references left.
 309 */
 310static void put_super(struct super_block *sb)
 311{
 312	spin_lock(&sb_lock);
 313	__put_super(sb);
 314	spin_unlock(&sb_lock);
 315}
 316
 317
 318/**
 319 *	deactivate_locked_super	-	drop an active reference to superblock
 320 *	@s: superblock to deactivate
 321 *
 322 *	Drops an active reference to superblock, converting it into a temporary
 323 *	one if there is no other active references left.  In that case we
 324 *	tell fs driver to shut it down and drop the temporary reference we
 325 *	had just acquired.
 326 *
 327 *	Caller holds exclusive lock on superblock; that lock is released.
 328 */
 329void deactivate_locked_super(struct super_block *s)
 330{
 331	struct file_system_type *fs = s->s_type;
 332	if (atomic_dec_and_test(&s->s_active)) {
 333		cleancache_invalidate_fs(s);
 334		unregister_shrinker(&s->s_shrink);
 335		fs->kill_sb(s);
 336
 337		/*
 338		 * Since list_lru_destroy() may sleep, we cannot call it from
 339		 * put_super(), where we hold the sb_lock. Therefore we destroy
 340		 * the lru lists right now.
 341		 */
 342		list_lru_destroy(&s->s_dentry_lru);
 343		list_lru_destroy(&s->s_inode_lru);
 344
 345		put_filesystem(fs);
 346		put_super(s);
 347	} else {
 348		up_write(&s->s_umount);
 349	}
 350}
 351
 352EXPORT_SYMBOL(deactivate_locked_super);
 353
 354/**
 355 *	deactivate_super	-	drop an active reference to superblock
 356 *	@s: superblock to deactivate
 357 *
 358 *	Variant of deactivate_locked_super(), except that superblock is *not*
 359 *	locked by caller.  If we are going to drop the final active reference,
 360 *	lock will be acquired prior to that.
 361 */
 362void deactivate_super(struct super_block *s)
 363{
 364	if (!atomic_add_unless(&s->s_active, -1, 1)) {
 365		down_write(&s->s_umount);
 366		deactivate_locked_super(s);
 367	}
 368}
 369
 370EXPORT_SYMBOL(deactivate_super);
 371
 372/**
 373 *	grab_super - acquire an active reference
 374 *	@s: reference we are trying to make active
 375 *
 376 *	Tries to acquire an active reference.  grab_super() is used when we
 377 * 	had just found a superblock in super_blocks or fs_type->fs_supers
 378 *	and want to turn it into a full-blown active reference.  grab_super()
 379 *	is called with sb_lock held and drops it.  Returns 1 in case of
 380 *	success, 0 if we had failed (superblock contents was already dead or
 381 *	dying when grab_super() had been called).  Note that this is only
 382 *	called for superblocks not in rundown mode (== ones still on ->fs_supers
 383 *	of their type), so increment of ->s_count is OK here.
 384 */
 385static int grab_super(struct super_block *s) __releases(sb_lock)
 386{
 387	s->s_count++;
 388	spin_unlock(&sb_lock);
 389	down_write(&s->s_umount);
 390	if ((s->s_flags & SB_BORN) && atomic_inc_not_zero(&s->s_active)) {
 391		put_super(s);
 392		return 1;
 393	}
 394	up_write(&s->s_umount);
 395	put_super(s);
 396	return 0;
 397}
 398
 399/*
 400 *	trylock_super - try to grab ->s_umount shared
 401 *	@sb: reference we are trying to grab
 402 *
 403 *	Try to prevent fs shutdown.  This is used in places where we
 404 *	cannot take an active reference but we need to ensure that the
 405 *	filesystem is not shut down while we are working on it. It returns
 406 *	false if we cannot acquire s_umount or if we lose the race and
 407 *	filesystem already got into shutdown, and returns true with the s_umount
 408 *	lock held in read mode in case of success. On successful return,
 409 *	the caller must drop the s_umount lock when done.
 410 *
 411 *	Note that unlike get_super() et.al. this one does *not* bump ->s_count.
 412 *	The reason why it's safe is that we are OK with doing trylock instead
 413 *	of down_read().  There's a couple of places that are OK with that, but
 414 *	it's very much not a general-purpose interface.
 415 */
 416bool trylock_super(struct super_block *sb)
 417{
 418	if (down_read_trylock(&sb->s_umount)) {
 419		if (!hlist_unhashed(&sb->s_instances) &&
 420		    sb->s_root && (sb->s_flags & SB_BORN))
 421			return true;
 422		up_read(&sb->s_umount);
 423	}
 424
 425	return false;
 426}
 427
 428/**
 429 *	generic_shutdown_super	-	common helper for ->kill_sb()
 430 *	@sb: superblock to kill
 431 *
 432 *	generic_shutdown_super() does all fs-independent work on superblock
 433 *	shutdown.  Typical ->kill_sb() should pick all fs-specific objects
 434 *	that need destruction out of superblock, call generic_shutdown_super()
 435 *	and release aforementioned objects.  Note: dentries and inodes _are_
 436 *	taken care of and do not need specific handling.
 437 *
 438 *	Upon calling this function, the filesystem may no longer alter or
 439 *	rearrange the set of dentries belonging to this super_block, nor may it
 440 *	change the attachments of dentries to inodes.
 441 */
 442void generic_shutdown_super(struct super_block *sb)
 443{
 444	const struct super_operations *sop = sb->s_op;
 445
 446	if (sb->s_root) {
 447		shrink_dcache_for_umount(sb);
 448		sync_filesystem(sb);
 449		sb->s_flags &= ~SB_ACTIVE;
 450
 
 451		cgroup_writeback_umount();
 452
 453		/* evict all inodes with zero refcount */
 454		evict_inodes(sb);
 455		/* only nonzero refcount inodes can have marks */
 456		fsnotify_sb_delete(sb);
 457
 458		if (sb->s_dio_done_wq) {
 459			destroy_workqueue(sb->s_dio_done_wq);
 460			sb->s_dio_done_wq = NULL;
 461		}
 462
 463		if (sop->put_super)
 464			sop->put_super(sb);
 465
 466		if (!list_empty(&sb->s_inodes)) {
 467			printk("VFS: Busy inodes after unmount of %s. "
 468			   "Self-destruct in 5 seconds.  Have a nice day...\n",
 469			   sb->s_id);
 470		}
 471	}
 472	spin_lock(&sb_lock);
 473	/* should be initialized for __put_super_and_need_restart() */
 474	hlist_del_init(&sb->s_instances);
 475	spin_unlock(&sb_lock);
 476	up_write(&sb->s_umount);
 477	if (sb->s_bdi != &noop_backing_dev_info) {
 478		bdi_put(sb->s_bdi);
 479		sb->s_bdi = &noop_backing_dev_info;
 480	}
 481}
 482
 483EXPORT_SYMBOL(generic_shutdown_super);
 484
 485bool mount_capable(struct fs_context *fc)
 486{
 487	if (!(fc->fs_type->fs_flags & FS_USERNS_MOUNT))
 488		return capable(CAP_SYS_ADMIN);
 489	else
 490		return ns_capable(fc->user_ns, CAP_SYS_ADMIN);
 491}
 492
 493/**
 494 * sget_fc - Find or create a superblock
 495 * @fc:	Filesystem context.
 496 * @test: Comparison callback
 497 * @set: Setup callback
 498 *
 499 * Find or create a superblock using the parameters stored in the filesystem
 500 * context and the two callback functions.
 501 *
 502 * If an extant superblock is matched, then that will be returned with an
 503 * elevated reference count that the caller must transfer or discard.
 504 *
 505 * If no match is made, a new superblock will be allocated and basic
 506 * initialisation will be performed (s_type, s_fs_info and s_id will be set and
 507 * the set() callback will be invoked), the superblock will be published and it
 508 * will be returned in a partially constructed state with SB_BORN and SB_ACTIVE
 509 * as yet unset.
 510 */
 511struct super_block *sget_fc(struct fs_context *fc,
 512			    int (*test)(struct super_block *, struct fs_context *),
 513			    int (*set)(struct super_block *, struct fs_context *))
 514{
 515	struct super_block *s = NULL;
 516	struct super_block *old;
 517	struct user_namespace *user_ns = fc->global ? &init_user_ns : fc->user_ns;
 518	int err;
 519
 520retry:
 521	spin_lock(&sb_lock);
 522	if (test) {
 523		hlist_for_each_entry(old, &fc->fs_type->fs_supers, s_instances) {
 524			if (test(old, fc))
 525				goto share_extant_sb;
 526		}
 527	}
 528	if (!s) {
 529		spin_unlock(&sb_lock);
 530		s = alloc_super(fc->fs_type, fc->sb_flags, user_ns);
 531		if (!s)
 532			return ERR_PTR(-ENOMEM);
 533		goto retry;
 534	}
 535
 536	s->s_fs_info = fc->s_fs_info;
 537	err = set(s, fc);
 538	if (err) {
 539		s->s_fs_info = NULL;
 540		spin_unlock(&sb_lock);
 541		destroy_unused_super(s);
 542		return ERR_PTR(err);
 543	}
 544	fc->s_fs_info = NULL;
 545	s->s_type = fc->fs_type;
 546	s->s_iflags |= fc->s_iflags;
 547	strlcpy(s->s_id, s->s_type->name, sizeof(s->s_id));
 548	list_add_tail(&s->s_list, &super_blocks);
 549	hlist_add_head(&s->s_instances, &s->s_type->fs_supers);
 550	spin_unlock(&sb_lock);
 551	get_filesystem(s->s_type);
 552	register_shrinker_prepared(&s->s_shrink);
 553	return s;
 554
 555share_extant_sb:
 556	if (user_ns != old->s_user_ns) {
 557		spin_unlock(&sb_lock);
 558		destroy_unused_super(s);
 559		return ERR_PTR(-EBUSY);
 560	}
 561	if (!grab_super(old))
 562		goto retry;
 563	destroy_unused_super(s);
 564	return old;
 565}
 566EXPORT_SYMBOL(sget_fc);
 567
 568/**
 569 *	sget	-	find or create a superblock
 570 *	@type:	  filesystem type superblock should belong to
 571 *	@test:	  comparison callback
 572 *	@set:	  setup callback
 573 *	@flags:	  mount flags
 574 *	@data:	  argument to each of them
 575 */
 576struct super_block *sget(struct file_system_type *type,
 577			int (*test)(struct super_block *,void *),
 578			int (*set)(struct super_block *,void *),
 579			int flags,
 580			void *data)
 581{
 582	struct user_namespace *user_ns = current_user_ns();
 583	struct super_block *s = NULL;
 584	struct super_block *old;
 585	int err;
 586
 587	/* We don't yet pass the user namespace of the parent
 588	 * mount through to here so always use &init_user_ns
 589	 * until that changes.
 590	 */
 591	if (flags & SB_SUBMOUNT)
 592		user_ns = &init_user_ns;
 593
 594retry:
 595	spin_lock(&sb_lock);
 596	if (test) {
 597		hlist_for_each_entry(old, &type->fs_supers, s_instances) {
 598			if (!test(old, data))
 599				continue;
 600			if (user_ns != old->s_user_ns) {
 601				spin_unlock(&sb_lock);
 602				destroy_unused_super(s);
 603				return ERR_PTR(-EBUSY);
 604			}
 605			if (!grab_super(old))
 606				goto retry;
 607			destroy_unused_super(s);
 608			return old;
 609		}
 610	}
 611	if (!s) {
 612		spin_unlock(&sb_lock);
 613		s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
 614		if (!s)
 615			return ERR_PTR(-ENOMEM);
 616		goto retry;
 617	}
 618
 619	err = set(s, data);
 620	if (err) {
 621		spin_unlock(&sb_lock);
 622		destroy_unused_super(s);
 623		return ERR_PTR(err);
 624	}
 625	s->s_type = type;
 626	strlcpy(s->s_id, type->name, sizeof(s->s_id));
 627	list_add_tail(&s->s_list, &super_blocks);
 628	hlist_add_head(&s->s_instances, &type->fs_supers);
 629	spin_unlock(&sb_lock);
 630	get_filesystem(type);
 631	register_shrinker_prepared(&s->s_shrink);
 632	return s;
 633}
 634EXPORT_SYMBOL(sget);
 635
 636void drop_super(struct super_block *sb)
 637{
 638	up_read(&sb->s_umount);
 639	put_super(sb);
 640}
 641
 642EXPORT_SYMBOL(drop_super);
 643
 644void drop_super_exclusive(struct super_block *sb)
 645{
 646	up_write(&sb->s_umount);
 647	put_super(sb);
 648}
 649EXPORT_SYMBOL(drop_super_exclusive);
 650
 651static void __iterate_supers(void (*f)(struct super_block *))
 652{
 653	struct super_block *sb, *p = NULL;
 654
 655	spin_lock(&sb_lock);
 656	list_for_each_entry(sb, &super_blocks, s_list) {
 657		if (hlist_unhashed(&sb->s_instances))
 658			continue;
 659		sb->s_count++;
 660		spin_unlock(&sb_lock);
 661
 662		f(sb);
 663
 664		spin_lock(&sb_lock);
 665		if (p)
 666			__put_super(p);
 667		p = sb;
 668	}
 669	if (p)
 670		__put_super(p);
 671	spin_unlock(&sb_lock);
 672}
 673/**
 674 *	iterate_supers - call function for all active superblocks
 675 *	@f: function to call
 676 *	@arg: argument to pass to it
 677 *
 678 *	Scans the superblock list and calls given function, passing it
 679 *	locked superblock and given argument.
 680 */
 681void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 682{
 683	struct super_block *sb, *p = NULL;
 684
 685	spin_lock(&sb_lock);
 686	list_for_each_entry(sb, &super_blocks, s_list) {
 687		if (hlist_unhashed(&sb->s_instances))
 688			continue;
 689		sb->s_count++;
 690		spin_unlock(&sb_lock);
 691
 692		down_read(&sb->s_umount);
 693		if (sb->s_root && (sb->s_flags & SB_BORN))
 694			f(sb, arg);
 695		up_read(&sb->s_umount);
 696
 697		spin_lock(&sb_lock);
 698		if (p)
 699			__put_super(p);
 700		p = sb;
 701	}
 702	if (p)
 703		__put_super(p);
 704	spin_unlock(&sb_lock);
 705}
 706
 707/**
 708 *	iterate_supers_type - call function for superblocks of given type
 709 *	@type: fs type
 710 *	@f: function to call
 711 *	@arg: argument to pass to it
 712 *
 713 *	Scans the superblock list and calls given function, passing it
 714 *	locked superblock and given argument.
 715 */
 716void iterate_supers_type(struct file_system_type *type,
 717	void (*f)(struct super_block *, void *), void *arg)
 718{
 719	struct super_block *sb, *p = NULL;
 720
 721	spin_lock(&sb_lock);
 722	hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
 723		sb->s_count++;
 724		spin_unlock(&sb_lock);
 725
 726		down_read(&sb->s_umount);
 727		if (sb->s_root && (sb->s_flags & SB_BORN))
 728			f(sb, arg);
 729		up_read(&sb->s_umount);
 730
 731		spin_lock(&sb_lock);
 732		if (p)
 733			__put_super(p);
 734		p = sb;
 735	}
 736	if (p)
 737		__put_super(p);
 738	spin_unlock(&sb_lock);
 739}
 740
 741EXPORT_SYMBOL(iterate_supers_type);
 742
 743static struct super_block *__get_super(struct block_device *bdev, bool excl)
 744{
 745	struct super_block *sb;
 746
 747	if (!bdev)
 748		return NULL;
 749
 750	spin_lock(&sb_lock);
 751rescan:
 752	list_for_each_entry(sb, &super_blocks, s_list) {
 753		if (hlist_unhashed(&sb->s_instances))
 754			continue;
 755		if (sb->s_bdev == bdev) {
 756			sb->s_count++;
 757			spin_unlock(&sb_lock);
 758			if (!excl)
 759				down_read(&sb->s_umount);
 760			else
 761				down_write(&sb->s_umount);
 762			/* still alive? */
 763			if (sb->s_root && (sb->s_flags & SB_BORN))
 764				return sb;
 765			if (!excl)
 766				up_read(&sb->s_umount);
 767			else
 768				up_write(&sb->s_umount);
 769			/* nope, got unmounted */
 770			spin_lock(&sb_lock);
 771			__put_super(sb);
 772			goto rescan;
 773		}
 774	}
 775	spin_unlock(&sb_lock);
 776	return NULL;
 777}
 778
 779/**
 780 *	get_super - get the superblock of a device
 781 *	@bdev: device to get the superblock for
 782 *
 783 *	Scans the superblock list and finds the superblock of the file system
 784 *	mounted on the device given. %NULL is returned if no match is found.
 785 */
 786struct super_block *get_super(struct block_device *bdev)
 787{
 788	return __get_super(bdev, false);
 789}
 790EXPORT_SYMBOL(get_super);
 791
 792static struct super_block *__get_super_thawed(struct block_device *bdev,
 793					      bool excl)
 794{
 795	while (1) {
 796		struct super_block *s = __get_super(bdev, excl);
 797		if (!s || s->s_writers.frozen == SB_UNFROZEN)
 798			return s;
 799		if (!excl)
 800			up_read(&s->s_umount);
 801		else
 802			up_write(&s->s_umount);
 803		wait_event(s->s_writers.wait_unfrozen,
 804			   s->s_writers.frozen == SB_UNFROZEN);
 805		put_super(s);
 806	}
 807}
 808
 809/**
 810 *	get_super_thawed - get thawed superblock of a device
 811 *	@bdev: device to get the superblock for
 812 *
 813 *	Scans the superblock list and finds the superblock of the file system
 814 *	mounted on the device. The superblock is returned once it is thawed
 815 *	(or immediately if it was not frozen). %NULL is returned if no match
 816 *	is found.
 817 */
 818struct super_block *get_super_thawed(struct block_device *bdev)
 819{
 820	return __get_super_thawed(bdev, false);
 821}
 822EXPORT_SYMBOL(get_super_thawed);
 823
 824/**
 825 *	get_super_exclusive_thawed - get thawed superblock of a device
 826 *	@bdev: device to get the superblock for
 827 *
 828 *	Scans the superblock list and finds the superblock of the file system
 829 *	mounted on the device. The superblock is returned once it is thawed
 830 *	(or immediately if it was not frozen) and s_umount semaphore is held
 831 *	in exclusive mode. %NULL is returned if no match is found.
 832 */
 833struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
 834{
 835	return __get_super_thawed(bdev, true);
 836}
 837EXPORT_SYMBOL(get_super_exclusive_thawed);
 838
 839/**
 840 * get_active_super - get an active reference to the superblock of a device
 841 * @bdev: device to get the superblock for
 842 *
 843 * Scans the superblock list and finds the superblock of the file system
 844 * mounted on the device given.  Returns the superblock with an active
 845 * reference or %NULL if none was found.
 846 */
 847struct super_block *get_active_super(struct block_device *bdev)
 848{
 849	struct super_block *sb;
 850
 851	if (!bdev)
 852		return NULL;
 853
 854restart:
 855	spin_lock(&sb_lock);
 856	list_for_each_entry(sb, &super_blocks, s_list) {
 857		if (hlist_unhashed(&sb->s_instances))
 858			continue;
 859		if (sb->s_bdev == bdev) {
 860			if (!grab_super(sb))
 861				goto restart;
 862			up_write(&sb->s_umount);
 863			return sb;
 864		}
 865	}
 866	spin_unlock(&sb_lock);
 867	return NULL;
 868}
 869
 870struct super_block *user_get_super(dev_t dev)
 871{
 872	struct super_block *sb;
 873
 874	spin_lock(&sb_lock);
 875rescan:
 876	list_for_each_entry(sb, &super_blocks, s_list) {
 877		if (hlist_unhashed(&sb->s_instances))
 878			continue;
 879		if (sb->s_dev ==  dev) {
 880			sb->s_count++;
 881			spin_unlock(&sb_lock);
 882			down_read(&sb->s_umount);
 883			/* still alive? */
 884			if (sb->s_root && (sb->s_flags & SB_BORN))
 885				return sb;
 886			up_read(&sb->s_umount);
 887			/* nope, got unmounted */
 888			spin_lock(&sb_lock);
 889			__put_super(sb);
 890			goto rescan;
 891		}
 892	}
 893	spin_unlock(&sb_lock);
 894	return NULL;
 895}
 896
 897/**
 898 * reconfigure_super - asks filesystem to change superblock parameters
 899 * @fc: The superblock and configuration
 900 *
 901 * Alters the configuration parameters of a live superblock.
 902 */
 903int reconfigure_super(struct fs_context *fc)
 904{
 905	struct super_block *sb = fc->root->d_sb;
 906	int retval;
 907	bool remount_ro = false;
 908	bool force = fc->sb_flags & SB_FORCE;
 909
 910	if (fc->sb_flags_mask & ~MS_RMT_MASK)
 911		return -EINVAL;
 912	if (sb->s_writers.frozen != SB_UNFROZEN)
 913		return -EBUSY;
 914
 915	retval = security_sb_remount(sb, fc->security);
 916	if (retval)
 917		return retval;
 918
 919	if (fc->sb_flags_mask & SB_RDONLY) {
 920#ifdef CONFIG_BLOCK
 921		if (!(fc->sb_flags & SB_RDONLY) && bdev_read_only(sb->s_bdev))
 922			return -EACCES;
 923#endif
 924
 925		remount_ro = (fc->sb_flags & SB_RDONLY) && !sb_rdonly(sb);
 926	}
 927
 928	if (remount_ro) {
 929		if (!hlist_empty(&sb->s_pins)) {
 930			up_write(&sb->s_umount);
 931			group_pin_kill(&sb->s_pins);
 932			down_write(&sb->s_umount);
 933			if (!sb->s_root)
 934				return 0;
 935			if (sb->s_writers.frozen != SB_UNFROZEN)
 936				return -EBUSY;
 937			remount_ro = !sb_rdonly(sb);
 938		}
 939	}
 940	shrink_dcache_sb(sb);
 941
 942	/* If we are reconfiguring to RDONLY and current sb is read/write,
 943	 * make sure there are no files open for writing.
 944	 */
 945	if (remount_ro) {
 946		if (force) {
 947			sb->s_readonly_remount = 1;
 948			smp_wmb();
 949		} else {
 950			retval = sb_prepare_remount_readonly(sb);
 951			if (retval)
 952				return retval;
 953		}
 954	}
 955
 956	if (fc->ops->reconfigure) {
 957		retval = fc->ops->reconfigure(fc);
 958		if (retval) {
 959			if (!force)
 960				goto cancel_readonly;
 961			/* If forced remount, go ahead despite any errors */
 962			WARN(1, "forced remount of a %s fs returned %i\n",
 963			     sb->s_type->name, retval);
 964		}
 965	}
 966
 967	WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) |
 968				 (fc->sb_flags & fc->sb_flags_mask)));
 969	/* Needs to be ordered wrt mnt_is_readonly() */
 970	smp_wmb();
 971	sb->s_readonly_remount = 0;
 972
 973	/*
 974	 * Some filesystems modify their metadata via some other path than the
 975	 * bdev buffer cache (eg. use a private mapping, or directories in
 976	 * pagecache, etc). Also file data modifications go via their own
 977	 * mappings. So If we try to mount readonly then copy the filesystem
 978	 * from bdev, we could get stale data, so invalidate it to give a best
 979	 * effort at coherency.
 980	 */
 981	if (remount_ro && sb->s_bdev)
 982		invalidate_bdev(sb->s_bdev);
 983	return 0;
 984
 985cancel_readonly:
 986	sb->s_readonly_remount = 0;
 987	return retval;
 988}
 989
 990static void do_emergency_remount_callback(struct super_block *sb)
 991{
 992	down_write(&sb->s_umount);
 993	if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
 994	    !sb_rdonly(sb)) {
 995		struct fs_context *fc;
 996
 997		fc = fs_context_for_reconfigure(sb->s_root,
 998					SB_RDONLY | SB_FORCE, SB_RDONLY);
 999		if (!IS_ERR(fc)) {
1000			if (parse_monolithic_mount_data(fc, NULL) == 0)
1001				(void)reconfigure_super(fc);
1002			put_fs_context(fc);
1003		}
1004	}
1005	up_write(&sb->s_umount);
1006}
1007
1008static void do_emergency_remount(struct work_struct *work)
1009{
1010	__iterate_supers(do_emergency_remount_callback);
1011	kfree(work);
1012	printk("Emergency Remount complete\n");
1013}
1014
1015void emergency_remount(void)
1016{
1017	struct work_struct *work;
1018
1019	work = kmalloc(sizeof(*work), GFP_ATOMIC);
1020	if (work) {
1021		INIT_WORK(work, do_emergency_remount);
1022		schedule_work(work);
1023	}
1024}
1025
1026static void do_thaw_all_callback(struct super_block *sb)
1027{
1028	down_write(&sb->s_umount);
1029	if (sb->s_root && sb->s_flags & SB_BORN) {
1030		emergency_thaw_bdev(sb);
1031		thaw_super_locked(sb);
1032	} else {
1033		up_write(&sb->s_umount);
1034	}
1035}
1036
1037static void do_thaw_all(struct work_struct *work)
1038{
1039	__iterate_supers(do_thaw_all_callback);
1040	kfree(work);
1041	printk(KERN_WARNING "Emergency Thaw complete\n");
1042}
1043
1044/**
1045 * emergency_thaw_all -- forcibly thaw every frozen filesystem
1046 *
1047 * Used for emergency unfreeze of all filesystems via SysRq
1048 */
1049void emergency_thaw_all(void)
1050{
1051	struct work_struct *work;
1052
1053	work = kmalloc(sizeof(*work), GFP_ATOMIC);
1054	if (work) {
1055		INIT_WORK(work, do_thaw_all);
1056		schedule_work(work);
1057	}
1058}
1059
1060static DEFINE_IDA(unnamed_dev_ida);
1061
1062/**
1063 * get_anon_bdev - Allocate a block device for filesystems which don't have one.
1064 * @p: Pointer to a dev_t.
1065 *
1066 * Filesystems which don't use real block devices can call this function
1067 * to allocate a virtual block device.
1068 *
1069 * Context: Any context.  Frequently called while holding sb_lock.
1070 * Return: 0 on success, -EMFILE if there are no anonymous bdevs left
1071 * or -ENOMEM if memory allocation failed.
1072 */
1073int get_anon_bdev(dev_t *p)
1074{
1075	int dev;
1076
1077	/*
1078	 * Many userspace utilities consider an FSID of 0 invalid.
1079	 * Always return at least 1 from get_anon_bdev.
1080	 */
1081	dev = ida_alloc_range(&unnamed_dev_ida, 1, (1 << MINORBITS) - 1,
1082			GFP_ATOMIC);
1083	if (dev == -ENOSPC)
1084		dev = -EMFILE;
1085	if (dev < 0)
1086		return dev;
1087
1088	*p = MKDEV(0, dev);
1089	return 0;
1090}
1091EXPORT_SYMBOL(get_anon_bdev);
1092
1093void free_anon_bdev(dev_t dev)
1094{
1095	ida_free(&unnamed_dev_ida, MINOR(dev));
1096}
1097EXPORT_SYMBOL(free_anon_bdev);
1098
1099int set_anon_super(struct super_block *s, void *data)
1100{
1101	return get_anon_bdev(&s->s_dev);
1102}
1103EXPORT_SYMBOL(set_anon_super);
1104
1105void kill_anon_super(struct super_block *sb)
1106{
1107	dev_t dev = sb->s_dev;
1108	generic_shutdown_super(sb);
1109	free_anon_bdev(dev);
1110}
1111EXPORT_SYMBOL(kill_anon_super);
1112
1113void kill_litter_super(struct super_block *sb)
1114{
1115	if (sb->s_root)
1116		d_genocide(sb->s_root);
1117	kill_anon_super(sb);
1118}
1119EXPORT_SYMBOL(kill_litter_super);
1120
1121int set_anon_super_fc(struct super_block *sb, struct fs_context *fc)
1122{
1123	return set_anon_super(sb, NULL);
1124}
1125EXPORT_SYMBOL(set_anon_super_fc);
1126
1127static int test_keyed_super(struct super_block *sb, struct fs_context *fc)
1128{
1129	return sb->s_fs_info == fc->s_fs_info;
1130}
1131
1132static int test_single_super(struct super_block *s, struct fs_context *fc)
1133{
1134	return 1;
1135}
1136
1137/**
1138 * vfs_get_super - Get a superblock with a search key set in s_fs_info.
1139 * @fc: The filesystem context holding the parameters
1140 * @keying: How to distinguish superblocks
1141 * @fill_super: Helper to initialise a new superblock
1142 *
1143 * Search for a superblock and create a new one if not found.  The search
1144 * criterion is controlled by @keying.  If the search fails, a new superblock
1145 * is created and @fill_super() is called to initialise it.
1146 *
1147 * @keying can take one of a number of values:
1148 *
1149 * (1) vfs_get_single_super - Only one superblock of this type may exist on the
1150 *     system.  This is typically used for special system filesystems.
1151 *
1152 * (2) vfs_get_keyed_super - Multiple superblocks may exist, but they must have
1153 *     distinct keys (where the key is in s_fs_info).  Searching for the same
1154 *     key again will turn up the superblock for that key.
1155 *
1156 * (3) vfs_get_independent_super - Multiple superblocks may exist and are
1157 *     unkeyed.  Each call will get a new superblock.
1158 *
1159 * A permissions check is made by sget_fc() unless we're getting a superblock
1160 * for a kernel-internal mount or a submount.
1161 */
1162int vfs_get_super(struct fs_context *fc,
1163		  enum vfs_get_super_keying keying,
1164		  int (*fill_super)(struct super_block *sb,
1165				    struct fs_context *fc))
1166{
1167	int (*test)(struct super_block *, struct fs_context *);
1168	struct super_block *sb;
1169	int err;
1170
1171	switch (keying) {
1172	case vfs_get_single_super:
1173	case vfs_get_single_reconf_super:
1174		test = test_single_super;
1175		break;
1176	case vfs_get_keyed_super:
1177		test = test_keyed_super;
1178		break;
1179	case vfs_get_independent_super:
1180		test = NULL;
1181		break;
1182	default:
1183		BUG();
1184	}
1185
1186	sb = sget_fc(fc, test, set_anon_super_fc);
1187	if (IS_ERR(sb))
1188		return PTR_ERR(sb);
1189
1190	if (!sb->s_root) {
1191		err = fill_super(sb, fc);
1192		if (err)
1193			goto error;
1194
1195		sb->s_flags |= SB_ACTIVE;
1196		fc->root = dget(sb->s_root);
1197	} else {
1198		fc->root = dget(sb->s_root);
1199		if (keying == vfs_get_single_reconf_super) {
1200			err = reconfigure_super(fc);
1201			if (err < 0) {
1202				dput(fc->root);
1203				fc->root = NULL;
1204				goto error;
1205			}
1206		}
1207	}
1208
1209	return 0;
1210
1211error:
1212	deactivate_locked_super(sb);
1213	return err;
1214}
1215EXPORT_SYMBOL(vfs_get_super);
1216
1217int get_tree_nodev(struct fs_context *fc,
1218		  int (*fill_super)(struct super_block *sb,
1219				    struct fs_context *fc))
1220{
1221	return vfs_get_super(fc, vfs_get_independent_super, fill_super);
1222}
1223EXPORT_SYMBOL(get_tree_nodev);
1224
1225int get_tree_single(struct fs_context *fc,
1226		  int (*fill_super)(struct super_block *sb,
1227				    struct fs_context *fc))
1228{
1229	return vfs_get_super(fc, vfs_get_single_super, fill_super);
1230}
1231EXPORT_SYMBOL(get_tree_single);
1232
1233int get_tree_single_reconf(struct fs_context *fc,
1234		  int (*fill_super)(struct super_block *sb,
1235				    struct fs_context *fc))
1236{
1237	return vfs_get_super(fc, vfs_get_single_reconf_super, fill_super);
1238}
1239EXPORT_SYMBOL(get_tree_single_reconf);
1240
1241int get_tree_keyed(struct fs_context *fc,
1242		  int (*fill_super)(struct super_block *sb,
1243				    struct fs_context *fc),
1244		void *key)
1245{
1246	fc->s_fs_info = key;
1247	return vfs_get_super(fc, vfs_get_keyed_super, fill_super);
1248}
1249EXPORT_SYMBOL(get_tree_keyed);
1250
1251#ifdef CONFIG_BLOCK
1252
1253static int set_bdev_super(struct super_block *s, void *data)
1254{
1255	s->s_bdev = data;
1256	s->s_dev = s->s_bdev->bd_dev;
1257	s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
1258
1259	return 0;
1260}
1261
1262static int set_bdev_super_fc(struct super_block *s, struct fs_context *fc)
1263{
1264	return set_bdev_super(s, fc->sget_key);
1265}
1266
1267static int test_bdev_super_fc(struct super_block *s, struct fs_context *fc)
1268{
1269	return s->s_bdev == fc->sget_key;
1270}
1271
1272/**
1273 * get_tree_bdev - Get a superblock based on a single block device
1274 * @fc: The filesystem context holding the parameters
1275 * @fill_super: Helper to initialise a new superblock
1276 */
1277int get_tree_bdev(struct fs_context *fc,
1278		int (*fill_super)(struct super_block *,
1279				  struct fs_context *))
1280{
1281	struct block_device *bdev;
1282	struct super_block *s;
1283	fmode_t mode = FMODE_READ | FMODE_EXCL;
1284	int error = 0;
1285
1286	if (!(fc->sb_flags & SB_RDONLY))
1287		mode |= FMODE_WRITE;
1288
1289	if (!fc->source)
1290		return invalf(fc, "No source specified");
1291
1292	bdev = blkdev_get_by_path(fc->source, mode, fc->fs_type);
1293	if (IS_ERR(bdev)) {
1294		errorf(fc, "%s: Can't open blockdev", fc->source);
1295		return PTR_ERR(bdev);
1296	}
1297
1298	/* Once the superblock is inserted into the list by sget_fc(), s_umount
1299	 * will protect the lockfs code from trying to start a snapshot while
1300	 * we are mounting
1301	 */
1302	mutex_lock(&bdev->bd_fsfreeze_mutex);
1303	if (bdev->bd_fsfreeze_count > 0) {
1304		mutex_unlock(&bdev->bd_fsfreeze_mutex);
1305		warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
1306		blkdev_put(bdev, mode);
 
1307		return -EBUSY;
1308	}
1309
1310	fc->sb_flags |= SB_NOSEC;
1311	fc->sget_key = bdev;
1312	s = sget_fc(fc, test_bdev_super_fc, set_bdev_super_fc);
1313	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1314	if (IS_ERR(s)) {
1315		blkdev_put(bdev, mode);
1316		return PTR_ERR(s);
1317	}
1318
1319	if (s->s_root) {
1320		/* Don't summarily change the RO/RW state. */
1321		if ((fc->sb_flags ^ s->s_flags) & SB_RDONLY) {
1322			warnf(fc, "%pg: Can't mount, would change RO state", bdev);
1323			deactivate_locked_super(s);
1324			blkdev_put(bdev, mode);
1325			return -EBUSY;
1326		}
1327
1328		/*
1329		 * s_umount nests inside bd_mutex during
1330		 * __invalidate_device().  blkdev_put() acquires
1331		 * bd_mutex and can't be called under s_umount.  Drop
1332		 * s_umount temporarily.  This is safe as we're
1333		 * holding an active reference.
1334		 */
1335		up_write(&s->s_umount);
1336		blkdev_put(bdev, mode);
1337		down_write(&s->s_umount);
1338	} else {
1339		s->s_mode = mode;
1340		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1341		sb_set_blocksize(s, block_size(bdev));
1342		error = fill_super(s, fc);
1343		if (error) {
1344			deactivate_locked_super(s);
1345			return error;
1346		}
1347
1348		s->s_flags |= SB_ACTIVE;
1349		bdev->bd_super = s;
1350	}
1351
1352	BUG_ON(fc->root);
1353	fc->root = dget(s->s_root);
1354	return 0;
1355}
1356EXPORT_SYMBOL(get_tree_bdev);
1357
1358static int test_bdev_super(struct super_block *s, void *data)
1359{
1360	return (void *)s->s_bdev == data;
1361}
1362
1363struct dentry *mount_bdev(struct file_system_type *fs_type,
1364	int flags, const char *dev_name, void *data,
1365	int (*fill_super)(struct super_block *, void *, int))
1366{
1367	struct block_device *bdev;
1368	struct super_block *s;
1369	fmode_t mode = FMODE_READ | FMODE_EXCL;
1370	int error = 0;
1371
1372	if (!(flags & SB_RDONLY))
1373		mode |= FMODE_WRITE;
1374
1375	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
1376	if (IS_ERR(bdev))
1377		return ERR_CAST(bdev);
1378
1379	/*
1380	 * once the super is inserted into the list by sget, s_umount
1381	 * will protect the lockfs code from trying to start a snapshot
1382	 * while we are mounting
1383	 */
1384	mutex_lock(&bdev->bd_fsfreeze_mutex);
1385	if (bdev->bd_fsfreeze_count > 0) {
1386		mutex_unlock(&bdev->bd_fsfreeze_mutex);
1387		error = -EBUSY;
1388		goto error_bdev;
1389	}
1390	s = sget(fs_type, test_bdev_super, set_bdev_super, flags | SB_NOSEC,
1391		 bdev);
1392	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1393	if (IS_ERR(s))
1394		goto error_s;
1395
1396	if (s->s_root) {
1397		if ((flags ^ s->s_flags) & SB_RDONLY) {
1398			deactivate_locked_super(s);
1399			error = -EBUSY;
1400			goto error_bdev;
1401		}
1402
1403		/*
1404		 * s_umount nests inside bd_mutex during
1405		 * __invalidate_device().  blkdev_put() acquires
1406		 * bd_mutex and can't be called under s_umount.  Drop
1407		 * s_umount temporarily.  This is safe as we're
1408		 * holding an active reference.
1409		 */
1410		up_write(&s->s_umount);
1411		blkdev_put(bdev, mode);
1412		down_write(&s->s_umount);
1413	} else {
1414		s->s_mode = mode;
1415		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1416		sb_set_blocksize(s, block_size(bdev));
1417		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1418		if (error) {
1419			deactivate_locked_super(s);
1420			goto error;
1421		}
1422
1423		s->s_flags |= SB_ACTIVE;
1424		bdev->bd_super = s;
1425	}
1426
1427	return dget(s->s_root);
1428
1429error_s:
1430	error = PTR_ERR(s);
1431error_bdev:
1432	blkdev_put(bdev, mode);
1433error:
1434	return ERR_PTR(error);
1435}
1436EXPORT_SYMBOL(mount_bdev);
1437
1438void kill_block_super(struct super_block *sb)
1439{
1440	struct block_device *bdev = sb->s_bdev;
1441	fmode_t mode = sb->s_mode;
1442
1443	bdev->bd_super = NULL;
1444	generic_shutdown_super(sb);
1445	sync_blockdev(bdev);
1446	WARN_ON_ONCE(!(mode & FMODE_EXCL));
1447	blkdev_put(bdev, mode | FMODE_EXCL);
1448}
1449
1450EXPORT_SYMBOL(kill_block_super);
1451#endif
1452
1453struct dentry *mount_nodev(struct file_system_type *fs_type,
1454	int flags, void *data,
1455	int (*fill_super)(struct super_block *, void *, int))
1456{
1457	int error;
1458	struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1459
1460	if (IS_ERR(s))
1461		return ERR_CAST(s);
1462
1463	error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1464	if (error) {
1465		deactivate_locked_super(s);
1466		return ERR_PTR(error);
1467	}
1468	s->s_flags |= SB_ACTIVE;
1469	return dget(s->s_root);
1470}
1471EXPORT_SYMBOL(mount_nodev);
1472
1473static int reconfigure_single(struct super_block *s,
1474			      int flags, void *data)
1475{
1476	struct fs_context *fc;
1477	int ret;
1478
1479	/* The caller really need to be passing fc down into mount_single(),
1480	 * then a chunk of this can be removed.  [Bollocks -- AV]
1481	 * Better yet, reconfiguration shouldn't happen, but rather the second
1482	 * mount should be rejected if the parameters are not compatible.
1483	 */
1484	fc = fs_context_for_reconfigure(s->s_root, flags, MS_RMT_MASK);
1485	if (IS_ERR(fc))
1486		return PTR_ERR(fc);
1487
1488	ret = parse_monolithic_mount_data(fc, data);
1489	if (ret < 0)
1490		goto out;
1491
1492	ret = reconfigure_super(fc);
1493out:
1494	put_fs_context(fc);
1495	return ret;
1496}
1497
1498static int compare_single(struct super_block *s, void *p)
1499{
1500	return 1;
1501}
1502
1503struct dentry *mount_single(struct file_system_type *fs_type,
1504	int flags, void *data,
1505	int (*fill_super)(struct super_block *, void *, int))
1506{
1507	struct super_block *s;
1508	int error;
1509
1510	s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1511	if (IS_ERR(s))
1512		return ERR_CAST(s);
1513	if (!s->s_root) {
1514		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1515		if (!error)
1516			s->s_flags |= SB_ACTIVE;
1517	} else {
1518		error = reconfigure_single(s, flags, data);
1519	}
1520	if (unlikely(error)) {
1521		deactivate_locked_super(s);
1522		return ERR_PTR(error);
1523	}
1524	return dget(s->s_root);
1525}
1526EXPORT_SYMBOL(mount_single);
1527
1528/**
1529 * vfs_get_tree - Get the mountable root
1530 * @fc: The superblock configuration context.
1531 *
1532 * The filesystem is invoked to get or create a superblock which can then later
1533 * be used for mounting.  The filesystem places a pointer to the root to be
1534 * used for mounting in @fc->root.
1535 */
1536int vfs_get_tree(struct fs_context *fc)
1537{
1538	struct super_block *sb;
1539	int error;
1540
1541	if (fc->root)
1542		return -EBUSY;
1543
1544	/* Get the mountable root in fc->root, with a ref on the root and a ref
1545	 * on the superblock.
1546	 */
1547	error = fc->ops->get_tree(fc);
1548	if (error < 0)
1549		return error;
1550
1551	if (!fc->root) {
1552		pr_err("Filesystem %s get_tree() didn't set fc->root\n",
1553		       fc->fs_type->name);
1554		/* We don't know what the locking state of the superblock is -
1555		 * if there is a superblock.
1556		 */
1557		BUG();
1558	}
1559
1560	sb = fc->root->d_sb;
1561	WARN_ON(!sb->s_bdi);
1562
1563	/*
1564	 * Write barrier is for super_cache_count(). We place it before setting
1565	 * SB_BORN as the data dependency between the two functions is the
1566	 * superblock structure contents that we just set up, not the SB_BORN
1567	 * flag.
1568	 */
1569	smp_wmb();
1570	sb->s_flags |= SB_BORN;
1571
1572	error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
1573	if (unlikely(error)) {
1574		fc_drop_locked(fc);
1575		return error;
1576	}
1577
1578	/*
1579	 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1580	 * but s_maxbytes was an unsigned long long for many releases. Throw
1581	 * this warning for a little while to try and catch filesystems that
1582	 * violate this rule.
1583	 */
1584	WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1585		"negative value (%lld)\n", fc->fs_type->name, sb->s_maxbytes);
1586
1587	return 0;
1588}
1589EXPORT_SYMBOL(vfs_get_tree);
1590
1591/*
1592 * Setup private BDI for given superblock. It gets automatically cleaned up
1593 * in generic_shutdown_super().
1594 */
1595int super_setup_bdi_name(struct super_block *sb, char *fmt, ...)
1596{
1597	struct backing_dev_info *bdi;
1598	int err;
1599	va_list args;
1600
1601	bdi = bdi_alloc(NUMA_NO_NODE);
1602	if (!bdi)
1603		return -ENOMEM;
 
 
1604
1605	va_start(args, fmt);
1606	err = bdi_register_va(bdi, fmt, args);
1607	va_end(args);
1608	if (err) {
1609		bdi_put(bdi);
1610		return err;
1611	}
1612	WARN_ON(sb->s_bdi != &noop_backing_dev_info);
1613	sb->s_bdi = bdi;
1614
1615	return 0;
1616}
1617EXPORT_SYMBOL(super_setup_bdi_name);
1618
1619/*
1620 * Setup private BDI for given superblock. I gets automatically cleaned up
1621 * in generic_shutdown_super().
1622 */
1623int super_setup_bdi(struct super_block *sb)
1624{
1625	static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
1626
1627	return super_setup_bdi_name(sb, "%.28s-%ld", sb->s_type->name,
1628				    atomic_long_inc_return(&bdi_seq));
1629}
1630EXPORT_SYMBOL(super_setup_bdi);
1631
1632/*
1633 * This is an internal function, please use sb_end_{write,pagefault,intwrite}
1634 * instead.
1635 */
1636void __sb_end_write(struct super_block *sb, int level)
1637{
1638	percpu_up_read(sb->s_writers.rw_sem + level-1);
1639}
1640EXPORT_SYMBOL(__sb_end_write);
1641
1642/*
1643 * This is an internal function, please use sb_start_{write,pagefault,intwrite}
1644 * instead.
1645 */
1646int __sb_start_write(struct super_block *sb, int level, bool wait)
1647{
1648	bool force_trylock = false;
1649	int ret = 1;
1650
1651#ifdef CONFIG_LOCKDEP
1652	/*
1653	 * We want lockdep to tell us about possible deadlocks with freezing
1654	 * but it's it bit tricky to properly instrument it. Getting a freeze
1655	 * protection works as getting a read lock but there are subtle
1656	 * problems. XFS for example gets freeze protection on internal level
1657	 * twice in some cases, which is OK only because we already hold a
1658	 * freeze protection also on higher level. Due to these cases we have
1659	 * to use wait == F (trylock mode) which must not fail.
1660	 */
1661	if (wait) {
1662		int i;
1663
1664		for (i = 0; i < level - 1; i++)
1665			if (percpu_rwsem_is_held(sb->s_writers.rw_sem + i)) {
1666				force_trylock = true;
1667				break;
1668			}
1669	}
1670#endif
1671	if (wait && !force_trylock)
1672		percpu_down_read(sb->s_writers.rw_sem + level-1);
1673	else
1674		ret = percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
1675
1676	WARN_ON(force_trylock && !ret);
1677	return ret;
1678}
1679EXPORT_SYMBOL(__sb_start_write);
1680
1681/**
1682 * sb_wait_write - wait until all writers to given file system finish
1683 * @sb: the super for which we wait
1684 * @level: type of writers we wait for (normal vs page fault)
1685 *
1686 * This function waits until there are no writers of given type to given file
1687 * system.
1688 */
1689static void sb_wait_write(struct super_block *sb, int level)
1690{
1691	percpu_down_write(sb->s_writers.rw_sem + level-1);
1692}
1693
1694/*
1695 * We are going to return to userspace and forget about these locks, the
1696 * ownership goes to the caller of thaw_super() which does unlock().
1697 */
1698static void lockdep_sb_freeze_release(struct super_block *sb)
1699{
1700	int level;
1701
1702	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1703		percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1704}
1705
1706/*
1707 * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
1708 */
1709static void lockdep_sb_freeze_acquire(struct super_block *sb)
1710{
1711	int level;
1712
1713	for (level = 0; level < SB_FREEZE_LEVELS; ++level)
1714		percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1715}
1716
1717static void sb_freeze_unlock(struct super_block *sb)
1718{
1719	int level;
1720
1721	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1722		percpu_up_write(sb->s_writers.rw_sem + level);
1723}
1724
1725/**
1726 * freeze_super - lock the filesystem and force it into a consistent state
1727 * @sb: the super to lock
1728 *
1729 * Syncs the super to make sure the filesystem is consistent and calls the fs's
1730 * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1731 * -EBUSY.
1732 *
1733 * During this function, sb->s_writers.frozen goes through these values:
1734 *
1735 * SB_UNFROZEN: File system is normal, all writes progress as usual.
1736 *
1737 * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
1738 * writes should be blocked, though page faults are still allowed. We wait for
1739 * all writes to complete and then proceed to the next stage.
1740 *
1741 * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1742 * but internal fs threads can still modify the filesystem (although they
1743 * should not dirty new pages or inodes), writeback can run etc. After waiting
1744 * for all running page faults we sync the filesystem which will clean all
1745 * dirty pages and inodes (no new dirty pages or inodes can be created when
1746 * sync is running).
1747 *
1748 * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1749 * modification are blocked (e.g. XFS preallocation truncation on inode
1750 * reclaim). This is usually implemented by blocking new transactions for
1751 * filesystems that have them and need this additional guard. After all
1752 * internal writers are finished we call ->freeze_fs() to finish filesystem
1753 * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1754 * mostly auxiliary for filesystems to verify they do not modify frozen fs.
1755 *
1756 * sb->s_writers.frozen is protected by sb->s_umount.
1757 */
1758int freeze_super(struct super_block *sb)
1759{
1760	int ret;
1761
1762	atomic_inc(&sb->s_active);
1763	down_write(&sb->s_umount);
1764	if (sb->s_writers.frozen != SB_UNFROZEN) {
1765		deactivate_locked_super(sb);
1766		return -EBUSY;
1767	}
1768
1769	if (!(sb->s_flags & SB_BORN)) {
1770		up_write(&sb->s_umount);
1771		return 0;	/* sic - it's "nothing to do" */
1772	}
1773
1774	if (sb_rdonly(sb)) {
1775		/* Nothing to do really... */
1776		sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1777		up_write(&sb->s_umount);
1778		return 0;
1779	}
1780
1781	sb->s_writers.frozen = SB_FREEZE_WRITE;
1782	/* Release s_umount to preserve sb_start_write -> s_umount ordering */
1783	up_write(&sb->s_umount);
1784	sb_wait_write(sb, SB_FREEZE_WRITE);
1785	down_write(&sb->s_umount);
1786
1787	/* Now we go and block page faults... */
1788	sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1789	sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1790
1791	/* All writers are done so after syncing there won't be dirty data */
1792	sync_filesystem(sb);
1793
1794	/* Now wait for internal filesystem counter */
1795	sb->s_writers.frozen = SB_FREEZE_FS;
1796	sb_wait_write(sb, SB_FREEZE_FS);
1797
1798	if (sb->s_op->freeze_fs) {
1799		ret = sb->s_op->freeze_fs(sb);
1800		if (ret) {
1801			printk(KERN_ERR
1802				"VFS:Filesystem freeze failed\n");
1803			sb->s_writers.frozen = SB_UNFROZEN;
1804			sb_freeze_unlock(sb);
1805			wake_up(&sb->s_writers.wait_unfrozen);
1806			deactivate_locked_super(sb);
1807			return ret;
1808		}
1809	}
1810	/*
1811	 * For debugging purposes so that fs can warn if it sees write activity
1812	 * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
1813	 */
1814	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1815	lockdep_sb_freeze_release(sb);
1816	up_write(&sb->s_umount);
1817	return 0;
1818}
1819EXPORT_SYMBOL(freeze_super);
1820
1821/**
1822 * thaw_super -- unlock filesystem
1823 * @sb: the super to thaw
1824 *
1825 * Unlocks the filesystem and marks it writeable again after freeze_super().
1826 */
1827static int thaw_super_locked(struct super_block *sb)
1828{
1829	int error;
1830
1831	if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
1832		up_write(&sb->s_umount);
1833		return -EINVAL;
1834	}
1835
1836	if (sb_rdonly(sb)) {
1837		sb->s_writers.frozen = SB_UNFROZEN;
1838		goto out;
1839	}
1840
1841	lockdep_sb_freeze_acquire(sb);
1842
1843	if (sb->s_op->unfreeze_fs) {
1844		error = sb->s_op->unfreeze_fs(sb);
1845		if (error) {
1846			printk(KERN_ERR
1847				"VFS:Filesystem thaw failed\n");
1848			lockdep_sb_freeze_release(sb);
1849			up_write(&sb->s_umount);
1850			return error;
1851		}
1852	}
1853
1854	sb->s_writers.frozen = SB_UNFROZEN;
1855	sb_freeze_unlock(sb);
1856out:
1857	wake_up(&sb->s_writers.wait_unfrozen);
1858	deactivate_locked_super(sb);
1859	return 0;
1860}
1861
1862int thaw_super(struct super_block *sb)
1863{
1864	down_write(&sb->s_umount);
1865	return thaw_super_locked(sb);
1866}
1867EXPORT_SYMBOL(thaw_super);