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