v4.19.13 snapshot.
diff --git a/fs/super.c b/fs/super.c
new file mode 100644
index 0000000..f3a8c00
--- /dev/null
+++ b/fs/super.c
@@ -0,0 +1,1582 @@
+// 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)
+{
+ bool force_trylock = false;
+ int ret = 1;
+
+#ifdef CONFIG_LOCKDEP
+ /*
+ * We want lockdep to tell us about possible deadlocks with freezing
+ * but it's it bit tricky to properly instrument it. Getting a freeze
+ * protection works as getting a read lock but there are subtle
+ * problems. XFS for example gets freeze protection on internal level
+ * twice in some cases, which is OK only because we already hold a
+ * freeze protection also on higher level. Due to these cases we have
+ * to use wait == F (trylock mode) which must not fail.
+ */
+ if (wait) {
+ int i;
+
+ for (i = 0; i < level - 1; i++)
+ if (percpu_rwsem_is_held(sb->s_writers.rw_sem + i)) {
+ force_trylock = true;
+ break;
+ }
+ }
+#endif
+ if (wait && !force_trylock)
+ percpu_down_read(sb->s_writers.rw_sem + level-1);
+ else
+ ret = percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
+
+ WARN_ON(force_trylock && !ret);
+ return ret;
+}
+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 = SB_FREEZE_LEVELS - 1; 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 */
+ sync_filesystem(sb);
+
+ /* 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);
+ 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);
+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);