Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1562 insertions, 0 deletions

diff --git a/fs/super.c b/fs/super.c
new file mode 100644
index 000000000..8dc26e23f
--- /dev/null
+++ b/fs/super.c
@@ -0,0 +1,1562 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/super.c
+ *
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ *
+ *  super.c contains code to handle: - mount structures
+ *                                   - super-block tables
+ *                                   - filesystem drivers list
+ *                                   - mount system call
+ *                                   - umount system call
+ *                                   - ustat system call
+ *
+ * GK 2/5/95  -  Changed to support mounting the root fs via NFS
+ *
+ *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
+ *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
+ *  Added options to /proc/mounts:
+ *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
+ *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
+ *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
+ */
+
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/blkdev.h>
+#include <linux/mount.h>
+#include <linux/security.h>
+#include <linux/writeback.h>		/* for the emergency remount stuff */
+#include <linux/idr.h>
+#include <linux/mutex.h>
+#include <linux/backing-dev.h>
+#include <linux/rculist_bl.h>
+#include <linux/cleancache.h>
+#include <linux/fsnotify.h>
+#include <linux/lockdep.h>
+#include <linux/user_namespace.h>
+#include "internal.h"
+
+static int thaw_super_locked(struct super_block *sb);
+
+static LIST_HEAD(super_blocks);
+static DEFINE_SPINLOCK(sb_lock);
+
+static char *sb_writers_name[SB_FREEZE_LEVELS] = {
+	"sb_writers",
+	"sb_pagefaults",
+	"sb_internal",
+};
+
+/*
+ * One thing we have to be careful of with a per-sb shrinker is that we don't
+ * drop the last active reference to the superblock from within the shrinker.
+ * If that happens we could trigger unregistering the shrinker from within the
+ * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
+ * take a passive reference to the superblock to avoid this from occurring.
+ */
+static unsigned long super_cache_scan(struct shrinker *shrink,
+				      struct shrink_control *sc)
+{
+	struct super_block *sb;
+	long	fs_objects = 0;
+	long	total_objects;
+	long	freed = 0;
+	long	dentries;
+	long	inodes;
+
+	sb = container_of(shrink, struct super_block, s_shrink);
+
+	/*
+	 * Deadlock avoidance.  We may hold various FS locks, and we don't want
+	 * to recurse into the FS that called us in clear_inode() and friends..
+	 */
+	if (!(sc->gfp_mask & __GFP_FS))
+		return SHRINK_STOP;
+
+	if (!trylock_super(sb))
+		return SHRINK_STOP;
+
+	if (sb->s_op->nr_cached_objects)
+		fs_objects = sb->s_op->nr_cached_objects(sb, sc);
+
+	inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
+	dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc);
+	total_objects = dentries + inodes + fs_objects + 1;
+	if (!total_objects)
+		total_objects = 1;
+
+	/* proportion the scan between the caches */
+	dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);
+	inodes = mult_frac(sc->nr_to_scan, inodes, total_objects);
+	fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
+
+	/*
+	 * prune the dcache first as the icache is pinned by it, then
+	 * prune the icache, followed by the filesystem specific caches
+	 *
+	 * Ensure that we always scan at least one object - memcg kmem
+	 * accounting uses this to fully empty the caches.
+	 */
+	sc->nr_to_scan = dentries + 1;
+	freed = prune_dcache_sb(sb, sc);
+	sc->nr_to_scan = inodes + 1;
+	freed += prune_icache_sb(sb, sc);
+
+	if (fs_objects) {
+		sc->nr_to_scan = fs_objects + 1;
+		freed += sb->s_op->free_cached_objects(sb, sc);
+	}
+
+	up_read(&sb->s_umount);
+	return freed;
+}
+
+static unsigned long super_cache_count(struct shrinker *shrink,
+				       struct shrink_control *sc)
+{
+	struct super_block *sb;
+	long	total_objects = 0;
+
+	sb = container_of(shrink, struct super_block, s_shrink);
+
+	/*
+	 * We don't call trylock_super() here as it is a scalability bottleneck,
+	 * so we're exposed to partial setup state. The shrinker rwsem does not
+	 * protect filesystem operations backing list_lru_shrink_count() or
+	 * s_op->nr_cached_objects(). Counts can change between
+	 * super_cache_count and super_cache_scan, so we really don't need locks
+	 * here.
+	 *
+	 * However, if we are currently mounting the superblock, the underlying
+	 * filesystem might be in a state of partial construction and hence it
+	 * is dangerous to access it.  trylock_super() uses a SB_BORN check to
+	 * avoid this situation, so do the same here. The memory barrier is
+	 * matched with the one in mount_fs() as we don't hold locks here.
+	 */
+	if (!(sb->s_flags & SB_BORN))
+		return 0;
+	smp_rmb();
+
+	if (sb->s_op && sb->s_op->nr_cached_objects)
+		total_objects = sb->s_op->nr_cached_objects(sb, sc);
+
+	total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
+	total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
+
+	if (!total_objects)
+		return SHRINK_EMPTY;
+
+	total_objects = vfs_pressure_ratio(total_objects);
+	return total_objects;
+}
+
+static void destroy_super_work(struct work_struct *work)
+{
+	struct super_block *s = container_of(work, struct super_block,
+							destroy_work);
+	int i;
+
+	for (i = 0; i < SB_FREEZE_LEVELS; i++)
+		percpu_free_rwsem(&s->s_writers.rw_sem[i]);
+	kfree(s);
+}
+
+static void destroy_super_rcu(struct rcu_head *head)
+{
+	struct super_block *s = container_of(head, struct super_block, rcu);
+	INIT_WORK(&s->destroy_work, destroy_super_work);
+	schedule_work(&s->destroy_work);
+}
+
+/* Free a superblock that has never been seen by anyone */
+static void destroy_unused_super(struct super_block *s)
+{
+	if (!s)
+		return;
+	up_write(&s->s_umount);
+	list_lru_destroy(&s->s_dentry_lru);
+	list_lru_destroy(&s->s_inode_lru);
+	security_sb_free(s);
+	put_user_ns(s->s_user_ns);
+	kfree(s->s_subtype);
+	free_prealloced_shrinker(&s->s_shrink);
+	/* no delays needed */
+	destroy_super_work(&s->destroy_work);
+}
+
+/**
+ *	alloc_super	-	create new superblock
+ *	@type:	filesystem type superblock should belong to
+ *	@flags: the mount flags
+ *	@user_ns: User namespace for the super_block
+ *
+ *	Allocates and initializes a new &struct super_block.  alloc_super()
+ *	returns a pointer new superblock or %NULL if allocation had failed.
+ */
+static struct super_block *alloc_super(struct file_system_type *type, int flags,
+				       struct user_namespace *user_ns)
+{
+	struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
+	static const struct super_operations default_op;
+	int i;
+
+	if (!s)
+		return NULL;
+
+	INIT_LIST_HEAD(&s->s_mounts);
+	s->s_user_ns = get_user_ns(user_ns);
+	init_rwsem(&s->s_umount);
+	lockdep_set_class(&s->s_umount, &type->s_umount_key);
+	/*
+	 * sget() can have s_umount recursion.
+	 *
+	 * When it cannot find a suitable sb, it allocates a new
+	 * one (this one), and tries again to find a suitable old
+	 * one.
+	 *
+	 * In case that succeeds, it will acquire the s_umount
+	 * lock of the old one. Since these are clearly distrinct
+	 * locks, and this object isn't exposed yet, there's no
+	 * risk of deadlocks.
+	 *
+	 * Annotate this by putting this lock in a different
+	 * subclass.
+	 */
+	down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
+
+	if (security_sb_alloc(s))
+		goto fail;
+
+	for (i = 0; i < SB_FREEZE_LEVELS; i++) {
+		if (__percpu_init_rwsem(&s->s_writers.rw_sem[i],
+					sb_writers_name[i],
+					&type->s_writers_key[i]))
+			goto fail;
+	}
+	init_waitqueue_head(&s->s_writers.wait_unfrozen);
+	s->s_bdi = &noop_backing_dev_info;
+	s->s_flags = flags;
+	if (s->s_user_ns != &init_user_ns)
+		s->s_iflags |= SB_I_NODEV;
+	INIT_HLIST_NODE(&s->s_instances);
+	INIT_HLIST_BL_HEAD(&s->s_roots);
+	mutex_init(&s->s_sync_lock);
+	INIT_LIST_HEAD(&s->s_inodes);
+	spin_lock_init(&s->s_inode_list_lock);
+	INIT_LIST_HEAD(&s->s_inodes_wb);
+	spin_lock_init(&s->s_inode_wblist_lock);
+
+	s->s_count = 1;
+	atomic_set(&s->s_active, 1);
+	mutex_init(&s->s_vfs_rename_mutex);
+	lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
+	init_rwsem(&s->s_dquot.dqio_sem);
+	s->s_maxbytes = MAX_NON_LFS;
+	s->s_op = &default_op;
+	s->s_time_gran = 1000000000;
+	s->cleancache_poolid = CLEANCACHE_NO_POOL;
+
+	s->s_shrink.seeks = DEFAULT_SEEKS;
+	s->s_shrink.scan_objects = super_cache_scan;
+	s->s_shrink.count_objects = super_cache_count;
+	s->s_shrink.batch = 1024;
+	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
+	if (prealloc_shrinker(&s->s_shrink))
+		goto fail;
+	if (list_lru_init_memcg(&s->s_dentry_lru, &s->s_shrink))
+		goto fail;
+	if (list_lru_init_memcg(&s->s_inode_lru, &s->s_shrink))
+		goto fail;
+	return s;
+
+fail:
+	destroy_unused_super(s);
+	return NULL;
+}
+
+/* Superblock refcounting  */
+
+/*
+ * Drop a superblock's refcount.  The caller must hold sb_lock.
+ */
+static void __put_super(struct super_block *s)
+{
+	if (!--s->s_count) {
+		list_del_init(&s->s_list);
+		WARN_ON(s->s_dentry_lru.node);
+		WARN_ON(s->s_inode_lru.node);
+		WARN_ON(!list_empty(&s->s_mounts));
+		security_sb_free(s);
+		put_user_ns(s->s_user_ns);
+		kfree(s->s_subtype);
+		call_rcu(&s->rcu, destroy_super_rcu);
+	}
+}
+
+/**
+ *	put_super	-	drop a temporary reference to superblock
+ *	@sb: superblock in question
+ *
+ *	Drops a temporary reference, frees superblock if there's no
+ *	references left.
+ */
+static void put_super(struct super_block *sb)
+{
+	spin_lock(&sb_lock);
+	__put_super(sb);
+	spin_unlock(&sb_lock);
+}
+
+
+/**
+ *	deactivate_locked_super	-	drop an active reference to superblock
+ *	@s: superblock to deactivate
+ *
+ *	Drops an active reference to superblock, converting it into a temporary
+ *	one if there is no other active references left.  In that case we
+ *	tell fs driver to shut it down and drop the temporary reference we
+ *	had just acquired.
+ *
+ *	Caller holds exclusive lock on superblock; that lock is released.
+ */
+void deactivate_locked_super(struct super_block *s)
+{
+	struct file_system_type *fs = s->s_type;
+	if (atomic_dec_and_test(&s->s_active)) {
+		cleancache_invalidate_fs(s);
+		unregister_shrinker(&s->s_shrink);
+		fs->kill_sb(s);
+
+		/*
+		 * Since list_lru_destroy() may sleep, we cannot call it from
+		 * put_super(), where we hold the sb_lock. Therefore we destroy
+		 * the lru lists right now.
+		 */
+		list_lru_destroy(&s->s_dentry_lru);
+		list_lru_destroy(&s->s_inode_lru);
+
+		put_filesystem(fs);
+		put_super(s);
+	} else {
+		up_write(&s->s_umount);
+	}
+}
+
+EXPORT_SYMBOL(deactivate_locked_super);
+
+/**
+ *	deactivate_super	-	drop an active reference to superblock
+ *	@s: superblock to deactivate
+ *
+ *	Variant of deactivate_locked_super(), except that superblock is *not*
+ *	locked by caller.  If we are going to drop the final active reference,
+ *	lock will be acquired prior to that.
+ */
+void deactivate_super(struct super_block *s)
+{
+        if (!atomic_add_unless(&s->s_active, -1, 1)) {
+		down_write(&s->s_umount);
+		deactivate_locked_super(s);
+	}
+}
+
+EXPORT_SYMBOL(deactivate_super);
+
+/**
+ *	grab_super - acquire an active reference
+ *	@s: reference we are trying to make active
+ *
+ *	Tries to acquire an active reference.  grab_super() is used when we
+ * 	had just found a superblock in super_blocks or fs_type->fs_supers
+ *	and want to turn it into a full-blown active reference.  grab_super()
+ *	is called with sb_lock held and drops it.  Returns 1 in case of
+ *	success, 0 if we had failed (superblock contents was already dead or
+ *	dying when grab_super() had been called).  Note that this is only
+ *	called for superblocks not in rundown mode (== ones still on ->fs_supers
+ *	of their type), so increment of ->s_count is OK here.
+ */
+static int grab_super(struct super_block *s) __releases(sb_lock)
+{
+	s->s_count++;
+	spin_unlock(&sb_lock);
+	down_write(&s->s_umount);
+	if ((s->s_flags & SB_BORN) && atomic_inc_not_zero(&s->s_active)) {
+		put_super(s);
+		return 1;
+	}
+	up_write(&s->s_umount);
+	put_super(s);
+	return 0;
+}
+
+/*
+ *	trylock_super - try to grab ->s_umount shared
+ *	@sb: reference we are trying to grab
+ *
+ *	Try to prevent fs shutdown.  This is used in places where we
+ *	cannot take an active reference but we need to ensure that the
+ *	filesystem is not shut down while we are working on it. It returns
+ *	false if we cannot acquire s_umount or if we lose the race and
+ *	filesystem already got into shutdown, and returns true with the s_umount
+ *	lock held in read mode in case of success. On successful return,
+ *	the caller must drop the s_umount lock when done.
+ *
+ *	Note that unlike get_super() et.al. this one does *not* bump ->s_count.
+ *	The reason why it's safe is that we are OK with doing trylock instead
+ *	of down_read().  There's a couple of places that are OK with that, but
+ *	it's very much not a general-purpose interface.
+ */
+bool trylock_super(struct super_block *sb)
+{
+	if (down_read_trylock(&sb->s_umount)) {
+		if (!hlist_unhashed(&sb->s_instances) &&
+		    sb->s_root && (sb->s_flags & SB_BORN))
+			return true;
+		up_read(&sb->s_umount);
+	}
+
+	return false;
+}
+
+/**
+ *	generic_shutdown_super	-	common helper for ->kill_sb()
+ *	@sb: superblock to kill
+ *
+ *	generic_shutdown_super() does all fs-independent work on superblock
+ *	shutdown.  Typical ->kill_sb() should pick all fs-specific objects
+ *	that need destruction out of superblock, call generic_shutdown_super()
+ *	and release aforementioned objects.  Note: dentries and inodes _are_
+ *	taken care of and do not need specific handling.
+ *
+ *	Upon calling this function, the filesystem may no longer alter or
+ *	rearrange the set of dentries belonging to this super_block, nor may it
+ *	change the attachments of dentries to inodes.
+ */
+void generic_shutdown_super(struct super_block *sb)
+{
+	const struct super_operations *sop = sb->s_op;
+
+	if (sb->s_root) {
+		shrink_dcache_for_umount(sb);
+		sync_filesystem(sb);
+		sb->s_flags &= ~SB_ACTIVE;
+
+		fsnotify_unmount_inodes(sb);
+		cgroup_writeback_umount();
+
+		evict_inodes(sb);
+
+		if (sb->s_dio_done_wq) {
+			destroy_workqueue(sb->s_dio_done_wq);
+			sb->s_dio_done_wq = NULL;
+		}
+
+		if (sop->put_super)
+			sop->put_super(sb);
+
+		if (!list_empty(&sb->s_inodes)) {
+			printk("VFS: Busy inodes after unmount of %s. "
+			   "Self-destruct in 5 seconds.  Have a nice day...\n",
+			   sb->s_id);
+		}
+	}
+	spin_lock(&sb_lock);
+	/* should be initialized for __put_super_and_need_restart() */
+	hlist_del_init(&sb->s_instances);
+	spin_unlock(&sb_lock);
+	up_write(&sb->s_umount);
+	if (sb->s_bdi != &noop_backing_dev_info) {
+		bdi_put(sb->s_bdi);
+		sb->s_bdi = &noop_backing_dev_info;
+	}
+}
+
+EXPORT_SYMBOL(generic_shutdown_super);
+
+/**
+ *	sget_userns -	find or create a superblock
+ *	@type:	filesystem type superblock should belong to
+ *	@test:	comparison callback
+ *	@set:	setup callback
+ *	@flags:	mount flags
+ *	@user_ns: User namespace for the super_block
+ *	@data:	argument to each of them
+ */
+struct super_block *sget_userns(struct file_system_type *type,
+			int (*test)(struct super_block *,void *),
+			int (*set)(struct super_block *,void *),
+			int flags, struct user_namespace *user_ns,
+			void *data)
+{
+	struct super_block *s = NULL;
+	struct super_block *old;
+	int err;
+
+	if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) &&
+	    !(type->fs_flags & FS_USERNS_MOUNT) &&
+	    !capable(CAP_SYS_ADMIN))
+		return ERR_PTR(-EPERM);
+retry:
+	spin_lock(&sb_lock);
+	if (test) {
+		hlist_for_each_entry(old, &type->fs_supers, s_instances) {
+			if (!test(old, data))
+				continue;
+			if (user_ns != old->s_user_ns) {
+				spin_unlock(&sb_lock);
+				destroy_unused_super(s);
+				return ERR_PTR(-EBUSY);
+			}
+			if (!grab_super(old))
+				goto retry;
+			destroy_unused_super(s);
+			return old;
+		}
+	}
+	if (!s) {
+		spin_unlock(&sb_lock);
+		s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
+		if (!s)
+			return ERR_PTR(-ENOMEM);
+		goto retry;
+	}
+
+	err = set(s, data);
+	if (err) {
+		spin_unlock(&sb_lock);
+		destroy_unused_super(s);
+		return ERR_PTR(err);
+	}
+	s->s_type = type;
+	strlcpy(s->s_id, type->name, sizeof(s->s_id));
+	list_add_tail(&s->s_list, &super_blocks);
+	hlist_add_head(&s->s_instances, &type->fs_supers);
+	spin_unlock(&sb_lock);
+	get_filesystem(type);
+	register_shrinker_prepared(&s->s_shrink);
+	return s;
+}
+
+EXPORT_SYMBOL(sget_userns);
+
+/**
+ *	sget	-	find or create a superblock
+ *	@type:	  filesystem type superblock should belong to
+ *	@test:	  comparison callback
+ *	@set:	  setup callback
+ *	@flags:	  mount flags
+ *	@data:	  argument to each of them
+ */
+struct super_block *sget(struct file_system_type *type,
+			int (*test)(struct super_block *,void *),
+			int (*set)(struct super_block *,void *),
+			int flags,
+			void *data)
+{
+	struct user_namespace *user_ns = current_user_ns();
+
+	/* We don't yet pass the user namespace of the parent
+	 * mount through to here so always use &init_user_ns
+	 * until that changes.
+	 */
+	if (flags & SB_SUBMOUNT)
+		user_ns = &init_user_ns;
+
+	/* Ensure the requestor has permissions over the target filesystem */
+	if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) && !ns_capable(user_ns, CAP_SYS_ADMIN))
+		return ERR_PTR(-EPERM);
+
+	return sget_userns(type, test, set, flags, user_ns, data);
+}
+
+EXPORT_SYMBOL(sget);
+
+void drop_super(struct super_block *sb)
+{
+	up_read(&sb->s_umount);
+	put_super(sb);
+}
+
+EXPORT_SYMBOL(drop_super);
+
+void drop_super_exclusive(struct super_block *sb)
+{
+	up_write(&sb->s_umount);
+	put_super(sb);
+}
+EXPORT_SYMBOL(drop_super_exclusive);
+
+static void __iterate_supers(void (*f)(struct super_block *))
+{
+	struct super_block *sb, *p = NULL;
+
+	spin_lock(&sb_lock);
+	list_for_each_entry(sb, &super_blocks, s_list) {
+		if (hlist_unhashed(&sb->s_instances))
+			continue;
+		sb->s_count++;
+		spin_unlock(&sb_lock);
+
+		f(sb);
+
+		spin_lock(&sb_lock);
+		if (p)
+			__put_super(p);
+		p = sb;
+	}
+	if (p)
+		__put_super(p);
+	spin_unlock(&sb_lock);
+}
+/**
+ *	iterate_supers - call function for all active superblocks
+ *	@f: function to call
+ *	@arg: argument to pass to it
+ *
+ *	Scans the superblock list and calls given function, passing it
+ *	locked superblock and given argument.
+ */
+void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
+{
+	struct super_block *sb, *p = NULL;
+
+	spin_lock(&sb_lock);
+	list_for_each_entry(sb, &super_blocks, s_list) {
+		if (hlist_unhashed(&sb->s_instances))
+			continue;
+		sb->s_count++;
+		spin_unlock(&sb_lock);
+
+		down_read(&sb->s_umount);
+		if (sb->s_root && (sb->s_flags & SB_BORN))
+			f(sb, arg);
+		up_read(&sb->s_umount);
+
+		spin_lock(&sb_lock);
+		if (p)
+			__put_super(p);
+		p = sb;
+	}
+	if (p)
+		__put_super(p);
+	spin_unlock(&sb_lock);
+}
+
+/**
+ *	iterate_supers_type - call function for superblocks of given type
+ *	@type: fs type
+ *	@f: function to call
+ *	@arg: argument to pass to it
+ *
+ *	Scans the superblock list and calls given function, passing it
+ *	locked superblock and given argument.
+ */
+void iterate_supers_type(struct file_system_type *type,
+	void (*f)(struct super_block *, void *), void *arg)
+{
+	struct super_block *sb, *p = NULL;
+
+	spin_lock(&sb_lock);
+	hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
+		sb->s_count++;
+		spin_unlock(&sb_lock);
+
+		down_read(&sb->s_umount);
+		if (sb->s_root && (sb->s_flags & SB_BORN))
+			f(sb, arg);
+		up_read(&sb->s_umount);
+
+		spin_lock(&sb_lock);
+		if (p)
+			__put_super(p);
+		p = sb;
+	}
+	if (p)
+		__put_super(p);
+	spin_unlock(&sb_lock);
+}
+
+EXPORT_SYMBOL(iterate_supers_type);
+
+static struct super_block *__get_super(struct block_device *bdev, bool excl)
+{
+	struct super_block *sb;
+
+	if (!bdev)
+		return NULL;
+
+	spin_lock(&sb_lock);
+rescan:
+	list_for_each_entry(sb, &super_blocks, s_list) {
+		if (hlist_unhashed(&sb->s_instances))
+			continue;
+		if (sb->s_bdev == bdev) {
+			sb->s_count++;
+			spin_unlock(&sb_lock);
+			if (!excl)
+				down_read(&sb->s_umount);
+			else
+				down_write(&sb->s_umount);
+			/* still alive? */
+			if (sb->s_root && (sb->s_flags & SB_BORN))
+				return sb;
+			if (!excl)
+				up_read(&sb->s_umount);
+			else
+				up_write(&sb->s_umount);
+			/* nope, got unmounted */
+			spin_lock(&sb_lock);
+			__put_super(sb);
+			goto rescan;
+		}
+	}
+	spin_unlock(&sb_lock);
+	return NULL;
+}
+
+/**
+ *	get_super - get the superblock of a device
+ *	@bdev: device to get the superblock for
+ *
+ *	Scans the superblock list and finds the superblock of the file system
+ *	mounted on the device given. %NULL is returned if no match is found.
+ */
+struct super_block *get_super(struct block_device *bdev)
+{
+	return __get_super(bdev, false);
+}
+EXPORT_SYMBOL(get_super);
+
+static struct super_block *__get_super_thawed(struct block_device *bdev,
+					      bool excl)
+{
+	while (1) {
+		struct super_block *s = __get_super(bdev, excl);
+		if (!s || s->s_writers.frozen == SB_UNFROZEN)
+			return s;
+		if (!excl)
+			up_read(&s->s_umount);
+		else
+			up_write(&s->s_umount);
+		wait_event(s->s_writers.wait_unfrozen,
+			   s->s_writers.frozen == SB_UNFROZEN);
+		put_super(s);
+	}
+}
+
+/**
+ *	get_super_thawed - get thawed superblock of a device
+ *	@bdev: device to get the superblock for
+ *
+ *	Scans the superblock list and finds the superblock of the file system
+ *	mounted on the device. The superblock is returned once it is thawed
+ *	(or immediately if it was not frozen). %NULL is returned if no match
+ *	is found.
+ */
+struct super_block *get_super_thawed(struct block_device *bdev)
+{
+	return __get_super_thawed(bdev, false);
+}
+EXPORT_SYMBOL(get_super_thawed);
+
+/**
+ *	get_super_exclusive_thawed - get thawed superblock of a device
+ *	@bdev: device to get the superblock for
+ *
+ *	Scans the superblock list and finds the superblock of the file system
+ *	mounted on the device. The superblock is returned once it is thawed
+ *	(or immediately if it was not frozen) and s_umount semaphore is held
+ *	in exclusive mode. %NULL is returned if no match is found.
+ */
+struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
+{
+	return __get_super_thawed(bdev, true);
+}
+EXPORT_SYMBOL(get_super_exclusive_thawed);
+
+/**
+ * get_active_super - get an active reference to the superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device given.  Returns the superblock with an active
+ * reference or %NULL if none was found.
+ */
+struct super_block *get_active_super(struct block_device *bdev)
+{
+	struct super_block *sb;
+
+	if (!bdev)
+		return NULL;
+
+restart:
+	spin_lock(&sb_lock);
+	list_for_each_entry(sb, &super_blocks, s_list) {
+		if (hlist_unhashed(&sb->s_instances))
+			continue;
+		if (sb->s_bdev == bdev) {
+			if (!grab_super(sb))
+				goto restart;
+			up_write(&sb->s_umount);
+			return sb;
+		}
+	}
+	spin_unlock(&sb_lock);
+	return NULL;
+}
+
+struct super_block *user_get_super(dev_t dev)
+{
+	struct super_block *sb;
+
+	spin_lock(&sb_lock);
+rescan:
+	list_for_each_entry(sb, &super_blocks, s_list) {
+		if (hlist_unhashed(&sb->s_instances))
+			continue;
+		if (sb->s_dev ==  dev) {
+			sb->s_count++;
+			spin_unlock(&sb_lock);
+			down_read(&sb->s_umount);
+			/* still alive? */
+			if (sb->s_root && (sb->s_flags & SB_BORN))
+				return sb;
+			up_read(&sb->s_umount);
+			/* nope, got unmounted */
+			spin_lock(&sb_lock);
+			__put_super(sb);
+			goto rescan;
+		}
+	}
+	spin_unlock(&sb_lock);
+	return NULL;
+}
+
+/**
+ *	do_remount_sb - asks filesystem to change mount options.
+ *	@sb:	superblock in question
+ *	@sb_flags: revised superblock flags
+ *	@data:	the rest of options
+ *      @force: whether or not to force the change
+ *
+ *	Alters the mount options of a mounted file system.
+ */
+int do_remount_sb(struct super_block *sb, int sb_flags, void *data, int force)
+{
+	int retval;
+	int remount_ro;
+
+	if (sb->s_writers.frozen != SB_UNFROZEN)
+		return -EBUSY;
+
+#ifdef CONFIG_BLOCK
+	if (!(sb_flags & SB_RDONLY) && bdev_read_only(sb->s_bdev))
+		return -EACCES;
+#endif
+
+	remount_ro = (sb_flags & SB_RDONLY) && !sb_rdonly(sb);
+
+	if (remount_ro) {
+		if (!hlist_empty(&sb->s_pins)) {
+			up_write(&sb->s_umount);
+			group_pin_kill(&sb->s_pins);
+			down_write(&sb->s_umount);
+			if (!sb->s_root)
+				return 0;
+			if (sb->s_writers.frozen != SB_UNFROZEN)
+				return -EBUSY;
+			remount_ro = (sb_flags & SB_RDONLY) && !sb_rdonly(sb);
+		}
+	}
+	shrink_dcache_sb(sb);
+
+	/* If we are remounting RDONLY and current sb is read/write,
+	   make sure there are no rw files opened */
+	if (remount_ro) {
+		if (force) {
+			sb->s_readonly_remount = 1;
+			smp_wmb();
+		} else {
+			retval = sb_prepare_remount_readonly(sb);
+			if (retval)
+				return retval;
+		}
+	}
+
+	if (sb->s_op->remount_fs) {
+		retval = sb->s_op->remount_fs(sb, &sb_flags, data);
+		if (retval) {
+			if (!force)
+				goto cancel_readonly;
+			/* If forced remount, go ahead despite any errors */
+			WARN(1, "forced remount of a %s fs returned %i\n",
+			     sb->s_type->name, retval);
+		}
+	}
+	sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (sb_flags & MS_RMT_MASK);
+	/* Needs to be ordered wrt mnt_is_readonly() */
+	smp_wmb();
+	sb->s_readonly_remount = 0;
+
+	/*
+	 * Some filesystems modify their metadata via some other path than the
+	 * bdev buffer cache (eg. use a private mapping, or directories in
+	 * pagecache, etc). Also file data modifications go via their own
+	 * mappings. So If we try to mount readonly then copy the filesystem
+	 * from bdev, we could get stale data, so invalidate it to give a best
+	 * effort at coherency.
+	 */
+	if (remount_ro && sb->s_bdev)
+		invalidate_bdev(sb->s_bdev);
+	return 0;
+
+cancel_readonly:
+	sb->s_readonly_remount = 0;
+	return retval;
+}
+
+static void do_emergency_remount_callback(struct super_block *sb)
+{
+	down_write(&sb->s_umount);
+	if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
+	    !sb_rdonly(sb)) {
+		/*
+		 * What lock protects sb->s_flags??
+		 */
+		do_remount_sb(sb, SB_RDONLY, NULL, 1);
+	}
+	up_write(&sb->s_umount);
+}
+
+static void do_emergency_remount(struct work_struct *work)
+{
+	__iterate_supers(do_emergency_remount_callback);
+	kfree(work);
+	printk("Emergency Remount complete\n");
+}
+
+void emergency_remount(void)
+{
+	struct work_struct *work;
+
+	work = kmalloc(sizeof(*work), GFP_ATOMIC);
+	if (work) {
+		INIT_WORK(work, do_emergency_remount);
+		schedule_work(work);
+	}
+}
+
+static void do_thaw_all_callback(struct super_block *sb)
+{
+	down_write(&sb->s_umount);
+	if (sb->s_root && sb->s_flags & SB_BORN) {
+		emergency_thaw_bdev(sb);
+		thaw_super_locked(sb);
+	} else {
+		up_write(&sb->s_umount);
+	}
+}
+
+static void do_thaw_all(struct work_struct *work)
+{
+	__iterate_supers(do_thaw_all_callback);
+	kfree(work);
+	printk(KERN_WARNING "Emergency Thaw complete\n");
+}
+
+/**
+ * emergency_thaw_all -- forcibly thaw every frozen filesystem
+ *
+ * Used for emergency unfreeze of all filesystems via SysRq
+ */
+void emergency_thaw_all(void)
+{
+	struct work_struct *work;
+
+	work = kmalloc(sizeof(*work), GFP_ATOMIC);
+	if (work) {
+		INIT_WORK(work, do_thaw_all);
+		schedule_work(work);
+	}
+}
+
+static DEFINE_IDA(unnamed_dev_ida);
+
+/**
+ * get_anon_bdev - Allocate a block device for filesystems which don't have one.
+ * @p: Pointer to a dev_t.
+ *
+ * Filesystems which don't use real block devices can call this function
+ * to allocate a virtual block device.
+ *
+ * Context: Any context.  Frequently called while holding sb_lock.
+ * Return: 0 on success, -EMFILE if there are no anonymous bdevs left
+ * or -ENOMEM if memory allocation failed.
+ */
+int get_anon_bdev(dev_t *p)
+{
+	int dev;
+
+	/*
+	 * Many userspace utilities consider an FSID of 0 invalid.
+	 * Always return at least 1 from get_anon_bdev.
+	 */
+	dev = ida_alloc_range(&unnamed_dev_ida, 1, (1 << MINORBITS) - 1,
+			GFP_ATOMIC);
+	if (dev == -ENOSPC)
+		dev = -EMFILE;
+	if (dev < 0)
+		return dev;
+
+	*p = MKDEV(0, dev);
+	return 0;
+}
+EXPORT_SYMBOL(get_anon_bdev);
+
+void free_anon_bdev(dev_t dev)
+{
+	ida_free(&unnamed_dev_ida, MINOR(dev));
+}
+EXPORT_SYMBOL(free_anon_bdev);
+
+int set_anon_super(struct super_block *s, void *data)
+{
+	return get_anon_bdev(&s->s_dev);
+}
+EXPORT_SYMBOL(set_anon_super);
+
+void kill_anon_super(struct super_block *sb)
+{
+	dev_t dev = sb->s_dev;
+	generic_shutdown_super(sb);
+	free_anon_bdev(dev);
+}
+EXPORT_SYMBOL(kill_anon_super);
+
+void kill_litter_super(struct super_block *sb)
+{
+	if (sb->s_root)
+		d_genocide(sb->s_root);
+	kill_anon_super(sb);
+}
+EXPORT_SYMBOL(kill_litter_super);
+
+static int ns_test_super(struct super_block *sb, void *data)
+{
+	return sb->s_fs_info == data;
+}
+
+static int ns_set_super(struct super_block *sb, void *data)
+{
+	sb->s_fs_info = data;
+	return set_anon_super(sb, NULL);
+}
+
+struct dentry *mount_ns(struct file_system_type *fs_type,
+	int flags, void *data, void *ns, struct user_namespace *user_ns,
+	int (*fill_super)(struct super_block *, void *, int))
+{
+	struct super_block *sb;
+
+	/* Don't allow mounting unless the caller has CAP_SYS_ADMIN
+	 * over the namespace.
+	 */
+	if (!(flags & SB_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN))
+		return ERR_PTR(-EPERM);
+
+	sb = sget_userns(fs_type, ns_test_super, ns_set_super, flags,
+			 user_ns, ns);
+	if (IS_ERR(sb))
+		return ERR_CAST(sb);
+
+	if (!sb->s_root) {
+		int err;
+		err = fill_super(sb, data, flags & SB_SILENT ? 1 : 0);
+		if (err) {
+			deactivate_locked_super(sb);
+			return ERR_PTR(err);
+		}
+
+		sb->s_flags |= SB_ACTIVE;
+	}
+
+	return dget(sb->s_root);
+}
+
+EXPORT_SYMBOL(mount_ns);
+
+#ifdef CONFIG_BLOCK
+static int set_bdev_super(struct super_block *s, void *data)
+{
+	s->s_bdev = data;
+	s->s_dev = s->s_bdev->bd_dev;
+	s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
+
+	return 0;
+}
+
+static int test_bdev_super(struct super_block *s, void *data)
+{
+	return (void *)s->s_bdev == data;
+}
+
+struct dentry *mount_bdev(struct file_system_type *fs_type,
+	int flags, const char *dev_name, void *data,
+	int (*fill_super)(struct super_block *, void *, int))
+{
+	struct block_device *bdev;
+	struct super_block *s;
+	fmode_t mode = FMODE_READ | FMODE_EXCL;
+	int error = 0;
+
+	if (!(flags & SB_RDONLY))
+		mode |= FMODE_WRITE;
+
+	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
+	if (IS_ERR(bdev))
+		return ERR_CAST(bdev);
+
+	/*
+	 * once the super is inserted into the list by sget, s_umount
+	 * will protect the lockfs code from trying to start a snapshot
+	 * while we are mounting
+	 */
+	mutex_lock(&bdev->bd_fsfreeze_mutex);
+	if (bdev->bd_fsfreeze_count > 0) {
+		mutex_unlock(&bdev->bd_fsfreeze_mutex);
+		error = -EBUSY;
+		goto error_bdev;
+	}
+	s = sget(fs_type, test_bdev_super, set_bdev_super, flags | SB_NOSEC,
+		 bdev);
+	mutex_unlock(&bdev->bd_fsfreeze_mutex);
+	if (IS_ERR(s))
+		goto error_s;
+
+	if (s->s_root) {
+		if ((flags ^ s->s_flags) & SB_RDONLY) {
+			deactivate_locked_super(s);
+			error = -EBUSY;
+			goto error_bdev;
+		}
+
+		/*
+		 * s_umount nests inside bd_mutex during
+		 * __invalidate_device().  blkdev_put() acquires
+		 * bd_mutex and can't be called under s_umount.  Drop
+		 * s_umount temporarily.  This is safe as we're
+		 * holding an active reference.
+		 */
+		up_write(&s->s_umount);
+		blkdev_put(bdev, mode);
+		down_write(&s->s_umount);
+	} else {
+		s->s_mode = mode;
+		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
+		sb_set_blocksize(s, block_size(bdev));
+		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
+		if (error) {
+			deactivate_locked_super(s);
+			goto error;
+		}
+
+		s->s_flags |= SB_ACTIVE;
+		bdev->bd_super = s;
+	}
+
+	return dget(s->s_root);
+
+error_s:
+	error = PTR_ERR(s);
+error_bdev:
+	blkdev_put(bdev, mode);
+error:
+	return ERR_PTR(error);
+}
+EXPORT_SYMBOL(mount_bdev);
+
+void kill_block_super(struct super_block *sb)
+{
+	struct block_device *bdev = sb->s_bdev;
+	fmode_t mode = sb->s_mode;
+
+	bdev->bd_super = NULL;
+	generic_shutdown_super(sb);
+	sync_blockdev(bdev);
+	WARN_ON_ONCE(!(mode & FMODE_EXCL));
+	blkdev_put(bdev, mode | FMODE_EXCL);
+}
+
+EXPORT_SYMBOL(kill_block_super);
+#endif
+
+struct dentry *mount_nodev(struct file_system_type *fs_type,
+	int flags, void *data,
+	int (*fill_super)(struct super_block *, void *, int))
+{
+	int error;
+	struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
+
+	if (IS_ERR(s))
+		return ERR_CAST(s);
+
+	error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
+	if (error) {
+		deactivate_locked_super(s);
+		return ERR_PTR(error);
+	}
+	s->s_flags |= SB_ACTIVE;
+	return dget(s->s_root);
+}
+EXPORT_SYMBOL(mount_nodev);
+
+static int compare_single(struct super_block *s, void *p)
+{
+	return 1;
+}
+
+struct dentry *mount_single(struct file_system_type *fs_type,
+	int flags, void *data,
+	int (*fill_super)(struct super_block *, void *, int))
+{
+	struct super_block *s;
+	int error;
+
+	s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
+	if (IS_ERR(s))
+		return ERR_CAST(s);
+	if (!s->s_root) {
+		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
+		if (error) {
+			deactivate_locked_super(s);
+			return ERR_PTR(error);
+		}
+		s->s_flags |= SB_ACTIVE;
+	} else {
+		do_remount_sb(s, flags, data, 0);
+	}
+	return dget(s->s_root);
+}
+EXPORT_SYMBOL(mount_single);
+
+struct dentry *
+mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
+{
+	struct dentry *root;
+	struct super_block *sb;
+	char *secdata = NULL;
+	int error = -ENOMEM;
+
+	if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
+		secdata = alloc_secdata();
+		if (!secdata)
+			goto out;
+
+		error = security_sb_copy_data(data, secdata);
+		if (error)
+			goto out_free_secdata;
+	}
+
+	root = type->mount(type, flags, name, data);
+	if (IS_ERR(root)) {
+		error = PTR_ERR(root);
+		goto out_free_secdata;
+	}
+	sb = root->d_sb;
+	BUG_ON(!sb);
+	WARN_ON(!sb->s_bdi);
+
+	/*
+	 * Write barrier is for super_cache_count(). We place it before setting
+	 * SB_BORN as the data dependency between the two functions is the
+	 * superblock structure contents that we just set up, not the SB_BORN
+	 * flag.
+	 */
+	smp_wmb();
+	sb->s_flags |= SB_BORN;
+
+	error = security_sb_kern_mount(sb, flags, secdata);
+	if (error)
+		goto out_sb;
+
+	/*
+	 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
+	 * but s_maxbytes was an unsigned long long for many releases. Throw
+	 * this warning for a little while to try and catch filesystems that
+	 * violate this rule.
+	 */
+	WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
+		"negative value (%lld)\n", type->name, sb->s_maxbytes);
+
+	up_write(&sb->s_umount);
+	free_secdata(secdata);
+	return root;
+out_sb:
+	dput(root);
+	deactivate_locked_super(sb);
+out_free_secdata:
+	free_secdata(secdata);
+out:
+	return ERR_PTR(error);
+}
+
+/*
+ * Setup private BDI for given superblock. It gets automatically cleaned up
+ * in generic_shutdown_super().
+ */
+int super_setup_bdi_name(struct super_block *sb, char *fmt, ...)
+{
+	struct backing_dev_info *bdi;
+	int err;
+	va_list args;
+
+	bdi = bdi_alloc(GFP_KERNEL);
+	if (!bdi)
+		return -ENOMEM;
+
+	bdi->name = sb->s_type->name;
+
+	va_start(args, fmt);
+	err = bdi_register_va(bdi, fmt, args);
+	va_end(args);
+	if (err) {
+		bdi_put(bdi);
+		return err;
+	}
+	WARN_ON(sb->s_bdi != &noop_backing_dev_info);
+	sb->s_bdi = bdi;
+
+	return 0;
+}
+EXPORT_SYMBOL(super_setup_bdi_name);
+
+/*
+ * Setup private BDI for given superblock. I gets automatically cleaned up
+ * in generic_shutdown_super().
+ */
+int super_setup_bdi(struct super_block *sb)
+{
+	static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
+
+	return super_setup_bdi_name(sb, "%.28s-%ld", sb->s_type->name,
+				    atomic_long_inc_return(&bdi_seq));
+}
+EXPORT_SYMBOL(super_setup_bdi);
+
+/*
+ * This is an internal function, please use sb_end_{write,pagefault,intwrite}
+ * instead.
+ */
+void __sb_end_write(struct super_block *sb, int level)
+{
+	percpu_up_read(sb->s_writers.rw_sem + level-1);
+}
+EXPORT_SYMBOL(__sb_end_write);
+
+/*
+ * This is an internal function, please use sb_start_{write,pagefault,intwrite}
+ * instead.
+ */
+int __sb_start_write(struct super_block *sb, int level, bool wait)
+{
+	if (!wait)
+		return percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
+
+	percpu_down_read(sb->s_writers.rw_sem + level-1);
+	return 1;
+}
+EXPORT_SYMBOL(__sb_start_write);
+
+/**
+ * sb_wait_write - wait until all writers to given file system finish
+ * @sb: the super for which we wait
+ * @level: type of writers we wait for (normal vs page fault)
+ *
+ * This function waits until there are no writers of given type to given file
+ * system.
+ */
+static void sb_wait_write(struct super_block *sb, int level)
+{
+	percpu_down_write(sb->s_writers.rw_sem + level-1);
+}
+
+/*
+ * We are going to return to userspace and forget about these locks, the
+ * ownership goes to the caller of thaw_super() which does unlock().
+ */
+static void lockdep_sb_freeze_release(struct super_block *sb)
+{
+	int level;
+
+	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
+		percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
+}
+
+/*
+ * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
+ */
+static void lockdep_sb_freeze_acquire(struct super_block *sb)
+{
+	int level;
+
+	for (level = 0; level < SB_FREEZE_LEVELS; ++level)
+		percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
+}
+
+static void sb_freeze_unlock(struct super_block *sb, int level)
+{
+	for (level--; level >= 0; level--)
+		percpu_up_write(sb->s_writers.rw_sem + level);
+}
+
+/**
+ * freeze_super - lock the filesystem and force it into a consistent state
+ * @sb: the super to lock
+ *
+ * Syncs the super to make sure the filesystem is consistent and calls the fs's
+ * freeze_fs.  Subsequent calls to this without first thawing the fs will return
+ * -EBUSY.
+ *
+ * During this function, sb->s_writers.frozen goes through these values:
+ *
+ * SB_UNFROZEN: File system is normal, all writes progress as usual.
+ *
+ * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
+ * writes should be blocked, though page faults are still allowed. We wait for
+ * all writes to complete and then proceed to the next stage.
+ *
+ * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
+ * but internal fs threads can still modify the filesystem (although they
+ * should not dirty new pages or inodes), writeback can run etc. After waiting
+ * for all running page faults we sync the filesystem which will clean all
+ * dirty pages and inodes (no new dirty pages or inodes can be created when
+ * sync is running).
+ *
+ * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
+ * modification are blocked (e.g. XFS preallocation truncation on inode
+ * reclaim). This is usually implemented by blocking new transactions for
+ * filesystems that have them and need this additional guard. After all
+ * internal writers are finished we call ->freeze_fs() to finish filesystem
+ * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
+ * mostly auxiliary for filesystems to verify they do not modify frozen fs.
+ *
+ * sb->s_writers.frozen is protected by sb->s_umount.
+ */
+int freeze_super(struct super_block *sb)
+{
+	int ret;
+
+	atomic_inc(&sb->s_active);
+	down_write(&sb->s_umount);
+	if (sb->s_writers.frozen != SB_UNFROZEN) {
+		deactivate_locked_super(sb);
+		return -EBUSY;
+	}
+
+	if (!(sb->s_flags & SB_BORN)) {
+		up_write(&sb->s_umount);
+		return 0;	/* sic - it's "nothing to do" */
+	}
+
+	if (sb_rdonly(sb)) {
+		/* Nothing to do really... */
+		sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+		up_write(&sb->s_umount);
+		return 0;
+	}
+
+	sb->s_writers.frozen = SB_FREEZE_WRITE;
+	/* Release s_umount to preserve sb_start_write -> s_umount ordering */
+	up_write(&sb->s_umount);
+	sb_wait_write(sb, SB_FREEZE_WRITE);
+	down_write(&sb->s_umount);
+
+	/* Now we go and block page faults... */
+	sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
+	sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
+
+	/* All writers are done so after syncing there won't be dirty data */
+	ret = sync_filesystem(sb);
+	if (ret) {
+		sb->s_writers.frozen = SB_UNFROZEN;
+		sb_freeze_unlock(sb, SB_FREEZE_PAGEFAULT);
+		wake_up(&sb->s_writers.wait_unfrozen);
+		deactivate_locked_super(sb);
+		return ret;
+	}
+
+	/* Now wait for internal filesystem counter */
+	sb->s_writers.frozen = SB_FREEZE_FS;
+	sb_wait_write(sb, SB_FREEZE_FS);
+
+	if (sb->s_op->freeze_fs) {
+		ret = sb->s_op->freeze_fs(sb);
+		if (ret) {
+			printk(KERN_ERR
+				"VFS:Filesystem freeze failed\n");
+			sb->s_writers.frozen = SB_UNFROZEN;
+			sb_freeze_unlock(sb, SB_FREEZE_FS);
+			wake_up(&sb->s_writers.wait_unfrozen);
+			deactivate_locked_super(sb);
+			return ret;
+		}
+	}
+	/*
+	 * For debugging purposes so that fs can warn if it sees write activity
+	 * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
+	 */
+	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+	lockdep_sb_freeze_release(sb);
+	up_write(&sb->s_umount);
+	return 0;
+}
+EXPORT_SYMBOL(freeze_super);
+
+/**
+ * thaw_super -- unlock filesystem
+ * @sb: the super to thaw
+ *
+ * Unlocks the filesystem and marks it writeable again after freeze_super().
+ */
+static int thaw_super_locked(struct super_block *sb)
+{
+	int error;
+
+	if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
+		up_write(&sb->s_umount);
+		return -EINVAL;
+	}
+
+	if (sb_rdonly(sb)) {
+		sb->s_writers.frozen = SB_UNFROZEN;
+		goto out;
+	}
+
+	lockdep_sb_freeze_acquire(sb);
+
+	if (sb->s_op->unfreeze_fs) {
+		error = sb->s_op->unfreeze_fs(sb);
+		if (error) {
+			printk(KERN_ERR
+				"VFS:Filesystem thaw failed\n");
+			lockdep_sb_freeze_release(sb);
+			up_write(&sb->s_umount);
+			return error;
+		}
+	}
+
+	sb->s_writers.frozen = SB_UNFROZEN;
+	sb_freeze_unlock(sb, SB_FREEZE_FS);
+out:
+	wake_up(&sb->s_writers.wait_unfrozen);
+	deactivate_locked_super(sb);
+	return 0;
+}
+
+int thaw_super(struct super_block *sb)
+{
+	down_write(&sb->s_umount);
+	return thaw_super_locked(sb);
+}
+EXPORT_SYMBOL(thaw_super);