* Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
*/
-#include <linux/module.h>
+#include <linux/export.h>
#include <linux/slab.h>
-#include <linux/init.h>
-#include <linux/smp_lock.h>
#include <linux/acct.h>
#include <linux/blkdev.h>
-#include <linux/quotaops.h>
-#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/security.h>
-#include <linux/syscalls.h>
-#include <linux/vfs.h>
#include <linux/writeback.h> /* for the emergency remount stuff */
#include <linux/idr.h>
-#include <linux/kobject.h>
#include <linux/mutex.h>
-#include <linux/file.h>
-#include <asm/uaccess.h>
+#include <linux/backing-dev.h>
+#include <linux/rculist_bl.h>
+#include <linux/cleancache.h>
+#include <linux/fsnotify.h>
+#include <linux/lockdep.h>
#include "internal.h"
LIST_HEAD(super_blocks);
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 int prune_super(struct shrinker *shrink, struct shrink_control *sc)
+{
+ struct super_block *sb;
+ int fs_objects = 0;
+ int total_objects;
+
+ 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->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
+ return -1;
+
+ if (!grab_super_passive(sb))
+ return -1;
+
+ if (sb->s_op && sb->s_op->nr_cached_objects)
+ fs_objects = sb->s_op->nr_cached_objects(sb);
+
+ total_objects = sb->s_nr_dentry_unused +
+ sb->s_nr_inodes_unused + fs_objects + 1;
+
+ if (sc->nr_to_scan) {
+ int dentries;
+ int inodes;
+
+ /* proportion the scan between the caches */
+ dentries = (sc->nr_to_scan * sb->s_nr_dentry_unused) /
+ total_objects;
+ inodes = (sc->nr_to_scan * sb->s_nr_inodes_unused) /
+ total_objects;
+ if (fs_objects)
+ fs_objects = (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
+ */
+ prune_dcache_sb(sb, dentries);
+ prune_icache_sb(sb, inodes);
+
+ if (fs_objects && sb->s_op->free_cached_objects) {
+ sb->s_op->free_cached_objects(sb, fs_objects);
+ fs_objects = sb->s_op->nr_cached_objects(sb);
+ }
+ total_objects = sb->s_nr_dentry_unused +
+ sb->s_nr_inodes_unused + fs_objects;
+ }
+
+ total_objects = (total_objects / 100) * sysctl_vfs_cache_pressure;
+ drop_super(sb);
+ return total_objects;
+}
+
+static int init_sb_writers(struct super_block *s, struct file_system_type *type)
+{
+ int err;
+ int i;
+
+ for (i = 0; i < SB_FREEZE_LEVELS; i++) {
+ err = percpu_counter_init(&s->s_writers.counter[i], 0);
+ if (err < 0)
+ goto err_out;
+ lockdep_init_map(&s->s_writers.lock_map[i], sb_writers_name[i],
+ &type->s_writers_key[i], 0);
+ }
+ init_waitqueue_head(&s->s_writers.wait);
+ init_waitqueue_head(&s->s_writers.wait_unfrozen);
+ return 0;
+err_out:
+ while (--i >= 0)
+ percpu_counter_destroy(&s->s_writers.counter[i]);
+ return err;
+}
+
+static void destroy_sb_writers(struct super_block *s)
+{
+ int i;
+
+ for (i = 0; i < SB_FREEZE_LEVELS; i++)
+ percpu_counter_destroy(&s->s_writers.counter[i]);
+}
+
/**
* alloc_super - create new superblock
* @type: filesystem type superblock should belong to
+ * @flags: the mount flags
*
* 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)
+static struct super_block *alloc_super(struct file_system_type *type, int flags)
{
struct super_block *s = kzalloc(sizeof(struct super_block), GFP_USER);
static const struct super_operations default_op;
if (s) {
if (security_sb_alloc(s)) {
+ /*
+ * We cannot call security_sb_free() without
+ * security_sb_alloc() succeeding. So bail out manually
+ */
kfree(s);
s = NULL;
goto out;
}
+#ifdef CONFIG_SMP
+ s->s_files = alloc_percpu(struct list_head);
+ if (!s->s_files)
+ goto err_out;
+ else {
+ int i;
+
+ for_each_possible_cpu(i)
+ INIT_LIST_HEAD(per_cpu_ptr(s->s_files, i));
+ }
+#else
INIT_LIST_HEAD(&s->s_files);
- INIT_LIST_HEAD(&s->s_instances);
- INIT_HLIST_HEAD(&s->s_anon);
+#endif
+ if (init_sb_writers(s, type))
+ goto err_out;
+ s->s_flags = flags;
+ s->s_bdi = &default_backing_dev_info;
+ INIT_HLIST_NODE(&s->s_instances);
+ INIT_HLIST_BL_HEAD(&s->s_anon);
INIT_LIST_HEAD(&s->s_inodes);
INIT_LIST_HEAD(&s->s_dentry_lru);
+ INIT_LIST_HEAD(&s->s_inode_lru);
+ spin_lock_init(&s->s_inode_lru_lock);
+ INIT_LIST_HEAD(&s->s_mounts);
init_rwsem(&s->s_umount);
- mutex_init(&s->s_lock);
lockdep_set_class(&s->s_umount, &type->s_umount_key);
- /*
- * The locking rules for s_lock are up to the
- * filesystem. For example ext3fs has different
- * lock ordering than usbfs:
- */
- lockdep_set_class(&s->s_lock, &type->s_lock_key);
/*
* sget() can have s_umount recursion.
*
* subclass.
*/
down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
- s->s_count = S_BIAS;
+ 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);
mutex_init(&s->s_dquot.dqio_mutex);
mutex_init(&s->s_dquot.dqonoff_mutex);
init_rwsem(&s->s_dquot.dqptr_sem);
- init_waitqueue_head(&s->s_wait_unfrozen);
s->s_maxbytes = MAX_NON_LFS;
- s->dq_op = sb_dquot_ops;
- s->s_qcop = sb_quotactl_ops;
s->s_op = &default_op;
s->s_time_gran = 1000000000;
+ s->cleancache_poolid = -1;
+
+ s->s_shrink.seeks = DEFAULT_SEEKS;
+ s->s_shrink.shrink = prune_super;
+ s->s_shrink.batch = 1024;
}
out:
return s;
+err_out:
+ security_sb_free(s);
+#ifdef CONFIG_SMP
+ if (s->s_files)
+ free_percpu(s->s_files);
+#endif
+ destroy_sb_writers(s);
+ kfree(s);
+ s = NULL;
+ goto out;
}
/**
*/
static inline void destroy_super(struct super_block *s)
{
+#ifdef CONFIG_SMP
+ free_percpu(s->s_files);
+#endif
+ destroy_sb_writers(s);
security_sb_free(s);
+ WARN_ON(!list_empty(&s->s_mounts));
kfree(s->s_subtype);
kfree(s->s_options);
kfree(s);
/* Superblock refcounting */
/*
- * Drop a superblock's refcount. Returns non-zero if the superblock was
- * destroyed. The caller must hold sb_lock.
+ * Drop a superblock's refcount. The caller must hold sb_lock.
*/
-static int __put_super(struct super_block *sb)
+static void __put_super(struct super_block *sb)
{
- int ret = 0;
-
if (!--sb->s_count) {
+ list_del_init(&sb->s_list);
destroy_super(sb);
- ret = 1;
- }
- return ret;
-}
-
-/*
- * Drop a superblock's refcount.
- * Returns non-zero if the superblock is about to be destroyed and
- * at least is already removed from super_blocks list, so if we are
- * making a loop through super blocks then we need to restart.
- * The caller must hold sb_lock.
- */
-int __put_super_and_need_restart(struct super_block *sb)
-{
- /* check for race with generic_shutdown_super() */
- if (list_empty(&sb->s_list)) {
- /* super block is removed, need to restart... */
- __put_super(sb);
- return 1;
}
- /* can't be the last, since s_list is still in use */
- sb->s_count--;
- BUG_ON(sb->s_count == 0);
- return 0;
}
/**
* Drops a temporary reference, frees superblock if there's no
* references left.
*/
-void put_super(struct super_block *sb)
+static void put_super(struct super_block *sb)
{
spin_lock(&sb_lock);
__put_super(sb);
/**
- * deactivate_super - drop an active reference to superblock
+ * deactivate_locked_super - drop an active reference to superblock
* @s: superblock to deactivate
*
- * Drops an active reference to superblock, acquiring a temprory one if
- * there is no active references left. In that case we lock superblock,
+ * Drops an active reference to superblock, converting it into a temprory
+ * 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_super(struct super_block *s)
+void deactivate_locked_super(struct super_block *s)
{
struct file_system_type *fs = s->s_type;
- if (atomic_dec_and_lock(&s->s_active, &sb_lock)) {
- s->s_count -= S_BIAS-1;
- spin_unlock(&sb_lock);
- vfs_dq_off(s, 0);
- down_write(&s->s_umount);
+ if (atomic_dec_and_test(&s->s_active)) {
+ cleancache_invalidate_fs(s);
fs->kill_sb(s);
+
+ /* caches are now gone, we can safely kill the shrinker now */
+ unregister_shrinker(&s->s_shrink);
put_filesystem(fs);
put_super(s);
+ } else {
+ up_write(&s->s_umount);
}
}
-EXPORT_SYMBOL(deactivate_super);
+EXPORT_SYMBOL(deactivate_locked_super);
/**
- * deactivate_locked_super - drop an active reference to superblock
+ * deactivate_super - drop an active reference to superblock
* @s: superblock to deactivate
*
- * Equivalent of up_write(&s->s_umount); deactivate_super(s);, except that
- * it does not unlock it until it's all over. As the result, it's safe to
- * use to dispose of new superblock on ->get_sb() failure exits - nobody
- * will see the sucker until it's all over. Equivalent using up_write +
- * deactivate_super is safe for that purpose only if superblock is either
- * safe to use or has NULL ->s_root when we unlock.
+ * 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_locked_super(struct super_block *s)
+void deactivate_super(struct super_block *s)
{
- struct file_system_type *fs = s->s_type;
- if (atomic_dec_and_lock(&s->s_active, &sb_lock)) {
- s->s_count -= S_BIAS-1;
- spin_unlock(&sb_lock);
- vfs_dq_off(s, 0);
- fs->kill_sb(s);
- put_filesystem(fs);
- put_super(s);
- } else {
- up_write(&s->s_umount);
+ if (!atomic_add_unless(&s->s_active, -1, 1)) {
+ down_write(&s->s_umount);
+ deactivate_locked_super(s);
}
}
-EXPORT_SYMBOL(deactivate_locked_super);
+EXPORT_SYMBOL(deactivate_super);
/**
* grab_super - acquire an active reference
*/
static int grab_super(struct super_block *s) __releases(sb_lock)
{
+ if (atomic_inc_not_zero(&s->s_active)) {
+ spin_unlock(&sb_lock);
+ return 1;
+ }
+ /* it's going away */
s->s_count++;
spin_unlock(&sb_lock);
+ /* wait for it to die */
down_write(&s->s_umount);
- if (s->s_root) {
- spin_lock(&sb_lock);
- if (s->s_count > S_BIAS) {
- atomic_inc(&s->s_active);
- s->s_count--;
- spin_unlock(&sb_lock);
- return 1;
- }
- spin_unlock(&sb_lock);
- }
up_write(&s->s_umount);
put_super(s);
- yield();
return 0;
}
/*
- * Superblock locking. We really ought to get rid of these two.
+ * grab_super_passive - acquire a passive reference
+ * @sb: reference we are trying to grab
+ *
+ * Tries to acquire a passive reference. This is used in places where we
+ * cannot take an active reference but we need to ensure that the
+ * superblock does not go away while we are working on it. It returns
+ * false if a reference was not gained, and returns true with the s_umount
+ * lock held in read mode if a reference is gained. On successful return,
+ * the caller must drop the s_umount lock and the passive reference when
+ * done.
*/
-void lock_super(struct super_block * sb)
+bool grab_super_passive(struct super_block *sb)
{
- get_fs_excl();
- mutex_lock(&sb->s_lock);
-}
+ spin_lock(&sb_lock);
+ if (hlist_unhashed(&sb->s_instances)) {
+ spin_unlock(&sb_lock);
+ return false;
+ }
-void unlock_super(struct super_block * sb)
-{
- put_fs_excl();
- mutex_unlock(&sb->s_lock);
-}
+ sb->s_count++;
+ spin_unlock(&sb_lock);
+
+ if (down_read_trylock(&sb->s_umount)) {
+ if (sb->s_root && (sb->s_flags & MS_BORN))
+ return true;
+ up_read(&sb->s_umount);
+ }
-EXPORT_SYMBOL(lock_super);
-EXPORT_SYMBOL(unlock_super);
+ put_super(sb);
+ return false;
+}
/**
* generic_shutdown_super - common helper for ->kill_sb()
{
const struct super_operations *sop = sb->s_op;
-
if (sb->s_root) {
shrink_dcache_for_umount(sb);
sync_filesystem(sb);
- get_fs_excl();
sb->s_flags &= ~MS_ACTIVE;
- /* bad name - it should be evict_inodes() */
- invalidate_inodes(sb);
+ fsnotify_unmount_inodes(&sb->s_inodes);
+
+ evict_inodes(sb);
if (sop->put_super)
sop->put_super(sb);
- /* Forget any remaining inodes */
- if (invalidate_inodes(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);
}
- put_fs_excl();
}
spin_lock(&sb_lock);
/* should be initialized for __put_super_and_need_restart() */
- list_del_init(&sb->s_list);
- list_del(&sb->s_instances);
+ hlist_del_init(&sb->s_instances);
spin_unlock(&sb_lock);
up_write(&sb->s_umount);
}
* @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 super_block *s = NULL;
retry:
spin_lock(&sb_lock);
if (test) {
- list_for_each_entry(old, &type->fs_supers, s_instances) {
+ hlist_for_each_entry(old, &type->fs_supers, s_instances) {
if (!test(old, data))
continue;
if (!grab_super(old))
if (s) {
up_write(&s->s_umount);
destroy_super(s);
+ s = NULL;
+ }
+ down_write(&old->s_umount);
+ if (unlikely(!(old->s_flags & MS_BORN))) {
+ deactivate_locked_super(old);
+ goto retry;
}
return old;
}
}
if (!s) {
spin_unlock(&sb_lock);
- s = alloc_super(type);
+ s = alloc_super(type, flags);
if (!s)
return ERR_PTR(-ENOMEM);
goto retry;
s->s_type = type;
strlcpy(s->s_id, type->name, sizeof(s->s_id));
list_add_tail(&s->s_list, &super_blocks);
- list_add(&s->s_instances, &type->fs_supers);
+ hlist_add_head(&s->s_instances, &type->fs_supers);
spin_unlock(&sb_lock);
get_filesystem(type);
+ register_shrinker(&s->s_shrink);
return s;
}
EXPORT_SYMBOL(drop_super);
/**
- * sync_supers - helper for periodic superblock writeback
- *
- * Call the write_super method if present on all dirty superblocks in
- * the system. This is for the periodic writeback used by most older
- * filesystems. For data integrity superblock writeback use
- * sync_filesystems() instead.
+ * iterate_supers - call function for all active superblocks
+ * @f: function to call
+ * @arg: argument to pass to it
*
- * Note: check the dirty flag before waiting, so we don't
- * hold up the sync while mounting a device. (The newly
- * mounted device won't need syncing.)
+ * Scans the superblock list and calls given function, passing it
+ * locked superblock and given argument.
*/
-void sync_supers(void)
+void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
{
- struct super_block *sb;
+ struct super_block *sb, *p = NULL;
spin_lock(&sb_lock);
-restart:
list_for_each_entry(sb, &super_blocks, s_list) {
- if (sb->s_op->write_super && sb->s_dirt) {
- sb->s_count++;
- spin_unlock(&sb_lock);
+ 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_dirt)
- sb->s_op->write_super(sb);
- up_read(&sb->s_umount);
+ down_read(&sb->s_umount);
+ if (sb->s_root && (sb->s_flags & MS_BORN))
+ f(sb, arg);
+ up_read(&sb->s_umount);
- spin_lock(&sb_lock);
- if (__put_super_and_need_restart(sb))
- goto restart;
- }
+ 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 & MS_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);
+
/**
* get_super - get the superblock of a device
* @bdev: device to get the superblock for
* mounted on the device given. %NULL is returned if no match is found.
*/
-struct super_block * get_super(struct block_device *bdev)
+struct super_block *get_super(struct block_device *bdev)
{
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_bdev == bdev) {
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
- if (sb->s_root)
+ /* still alive? */
+ if (sb->s_root && (sb->s_flags & MS_BORN))
return sb;
up_read(&sb->s_umount);
- /* restart only when sb is no longer on the list */
+ /* nope, got unmounted */
spin_lock(&sb_lock);
- if (__put_super_and_need_restart(sb))
- goto rescan;
+ __put_super(sb);
+ goto rescan;
}
}
spin_unlock(&sb_lock);
}
EXPORT_SYMBOL(get_super);
+
+/**
+ * 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)
+{
+ while (1) {
+ struct super_block *s = get_super(bdev);
+ if (!s || s->s_writers.frozen == SB_UNFROZEN)
+ return s;
+ up_read(&s->s_umount);
+ wait_event(s->s_writers.wait_unfrozen,
+ s->s_writers.frozen == SB_UNFROZEN);
+ put_super(s);
+ }
+}
+EXPORT_SYMBOL(get_super_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)) /* drops sb_lock */
+ return sb;
+ else
+ goto restart;
+ }
+ }
+ spin_unlock(&sb_lock);
+ return NULL;
+}
-struct super_block * user_get_super(dev_t dev)
+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);
- if (sb->s_root)
+ /* still alive? */
+ if (sb->s_root && (sb->s_flags & MS_BORN))
return sb;
up_read(&sb->s_umount);
- /* restart only when sb is no longer on the list */
+ /* nope, got unmounted */
spin_lock(&sb_lock);
- if (__put_super_and_need_restart(sb))
- goto rescan;
+ __put_super(sb);
+ goto rescan;
}
}
spin_unlock(&sb_lock);
return NULL;
}
-SYSCALL_DEFINE2(ustat, unsigned, dev, struct ustat __user *, ubuf)
-{
- struct super_block *s;
- struct ustat tmp;
- struct kstatfs sbuf;
- int err = -EINVAL;
-
- s = user_get_super(new_decode_dev(dev));
- if (s == NULL)
- goto out;
- err = vfs_statfs(s->s_root, &sbuf);
- drop_super(s);
- if (err)
- goto out;
-
- memset(&tmp,0,sizeof(struct ustat));
- tmp.f_tfree = sbuf.f_bfree;
- tmp.f_tinode = sbuf.f_ffree;
-
- err = copy_to_user(ubuf,&tmp,sizeof(struct ustat)) ? -EFAULT : 0;
-out:
- return err;
-}
-
/**
* do_remount_sb - asks filesystem to change mount options.
* @sb: superblock in question
int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
{
int retval;
- int remount_rw;
-
+ int remount_ro;
+
+ if (sb->s_writers.frozen != SB_UNFROZEN)
+ return -EBUSY;
+
#ifdef CONFIG_BLOCK
if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
return -EACCES;
#endif
+
if (flags & MS_RDONLY)
acct_auto_close(sb);
shrink_dcache_sb(sb);
sync_filesystem(sb);
+ remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
+
/* If we are remounting RDONLY and current sb is read/write,
make sure there are no rw files opened */
- if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY)) {
- if (force)
+ if (remount_ro) {
+ if (force) {
mark_files_ro(sb);
- else if (!fs_may_remount_ro(sb))
- return -EBUSY;
- retval = vfs_dq_off(sb, 1);
- if (retval < 0 && retval != -ENOSYS)
- return -EBUSY;
+ } else {
+ retval = sb_prepare_remount_readonly(sb);
+ if (retval)
+ return retval;
+ }
}
- remount_rw = !(flags & MS_RDONLY) && (sb->s_flags & MS_RDONLY);
if (sb->s_op->remount_fs) {
retval = sb->s_op->remount_fs(sb, &flags, data);
- if (retval)
- return retval;
+ 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) | (flags & MS_RMT_MASK);
- if (remount_rw)
- vfs_dq_quota_on_remount(sb);
+ /* 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(struct work_struct *work)
{
- struct super_block *sb;
+ 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_write(&sb->s_umount);
- if (sb->s_root && sb->s_bdev && !(sb->s_flags & MS_RDONLY)) {
+ if (sb->s_root && sb->s_bdev && (sb->s_flags & MS_BORN) &&
+ !(sb->s_flags & MS_RDONLY)) {
/*
- * ->remount_fs needs lock_kernel().
- *
* What lock protects sb->s_flags??
*/
do_remount_sb(sb, MS_RDONLY, NULL, 1);
}
up_write(&sb->s_umount);
- put_super(sb);
spin_lock(&sb_lock);
+ if (p)
+ __put_super(p);
+ p = sb;
}
+ if (p)
+ __put_super(p);
spin_unlock(&sb_lock);
kfree(work);
printk("Emergency Remount complete\n");
static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
static int unnamed_dev_start = 0; /* don't bother trying below it */
-int set_anon_super(struct super_block *s, void *data)
+int get_anon_bdev(dev_t *p)
{
int dev;
int error;
else if (error)
return -EAGAIN;
- if ((dev & MAX_ID_MASK) == (1 << MINORBITS)) {
+ if (dev == (1 << MINORBITS)) {
spin_lock(&unnamed_dev_lock);
ida_remove(&unnamed_dev_ida, dev);
if (unnamed_dev_start > dev)
spin_unlock(&unnamed_dev_lock);
return -EMFILE;
}
- s->s_dev = MKDEV(0, dev & MINORMASK);
+ *p = MKDEV(0, dev & MINORMASK);
return 0;
}
+EXPORT_SYMBOL(get_anon_bdev);
-EXPORT_SYMBOL(set_anon_super);
-
-void kill_anon_super(struct super_block *sb)
+void free_anon_bdev(dev_t dev)
{
- int slot = MINOR(sb->s_dev);
-
- generic_shutdown_super(sb);
+ int slot = MINOR(dev);
spin_lock(&unnamed_dev_lock);
ida_remove(&unnamed_dev_ida, slot);
if (slot < unnamed_dev_start)
unnamed_dev_start = slot;
spin_unlock(&unnamed_dev_lock);
}
+EXPORT_SYMBOL(free_anon_bdev);
+
+int set_anon_super(struct super_block *s, void *data)
+{
+ int error = get_anon_bdev(&s->s_dev);
+ if (!error)
+ s->s_bdi = &noop_backing_dev_info;
+ return error;
+}
+
+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);
return set_anon_super(sb, NULL);
}
-int get_sb_ns(struct file_system_type *fs_type, int flags, void *data,
- int (*fill_super)(struct super_block *, void *, int),
- struct vfsmount *mnt)
+struct dentry *mount_ns(struct file_system_type *fs_type, int flags,
+ void *data, int (*fill_super)(struct super_block *, void *, int))
{
struct super_block *sb;
- sb = sget(fs_type, ns_test_super, ns_set_super, data);
+ sb = sget(fs_type, ns_test_super, ns_set_super, flags, data);
if (IS_ERR(sb))
- return PTR_ERR(sb);
+ return ERR_CAST(sb);
if (!sb->s_root) {
int err;
- sb->s_flags = flags;
err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
if (err) {
deactivate_locked_super(sb);
- return err;
+ return ERR_PTR(err);
}
sb->s_flags |= MS_ACTIVE;
}
- simple_set_mnt(mnt, sb);
- return 0;
+ return dget(sb->s_root);
}
-EXPORT_SYMBOL(get_sb_ns);
+EXPORT_SYMBOL(mount_ns);
#ifdef CONFIG_BLOCK
static int set_bdev_super(struct super_block *s, void *data)
return (void *)s->s_bdev == data;
}
-int get_sb_bdev(struct file_system_type *fs_type,
+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 vfsmount *mnt)
+ int (*fill_super)(struct super_block *, void *, int))
{
struct block_device *bdev;
struct super_block *s;
- fmode_t mode = FMODE_READ;
+ fmode_t mode = FMODE_READ | FMODE_EXCL;
int error = 0;
if (!(flags & MS_RDONLY))
mode |= FMODE_WRITE;
- bdev = open_bdev_exclusive(dev_name, mode, fs_type);
+ bdev = blkdev_get_by_path(dev_name, mode, fs_type);
if (IS_ERR(bdev))
- return PTR_ERR(bdev);
+ return ERR_CAST(bdev);
/*
* once the super is inserted into the list by sget, s_umount
error = -EBUSY;
goto error_bdev;
}
- s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
+ s = sget(fs_type, test_bdev_super, set_bdev_super, flags | MS_NOSEC,
+ bdev);
mutex_unlock(&bdev->bd_fsfreeze_mutex);
if (IS_ERR(s))
goto error_s;
goto error_bdev;
}
- close_bdev_exclusive(bdev, mode);
+ /*
+ * 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 {
char b[BDEVNAME_SIZE];
- s->s_flags = flags;
s->s_mode = mode;
strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
sb_set_blocksize(s, block_size(bdev));
bdev->bd_super = s;
}
- simple_set_mnt(mnt, s);
- return 0;
+ return dget(s->s_root);
error_s:
error = PTR_ERR(s);
error_bdev:
- close_bdev_exclusive(bdev, mode);
+ blkdev_put(bdev, mode);
error:
- return error;
+ return ERR_PTR(error);
}
-
-EXPORT_SYMBOL(get_sb_bdev);
+EXPORT_SYMBOL(mount_bdev);
void kill_block_super(struct super_block *sb)
{
bdev->bd_super = NULL;
generic_shutdown_super(sb);
sync_blockdev(bdev);
- close_bdev_exclusive(bdev, mode);
+ WARN_ON_ONCE(!(mode & FMODE_EXCL));
+ blkdev_put(bdev, mode | FMODE_EXCL);
}
EXPORT_SYMBOL(kill_block_super);
#endif
-int get_sb_nodev(struct file_system_type *fs_type,
+struct dentry *mount_nodev(struct file_system_type *fs_type,
int flags, void *data,
- int (*fill_super)(struct super_block *, void *, int),
- struct vfsmount *mnt)
+ int (*fill_super)(struct super_block *, void *, int))
{
int error;
- struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);
+ struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
if (IS_ERR(s))
- return PTR_ERR(s);
-
- s->s_flags = flags;
+ return ERR_CAST(s);
error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
if (error) {
deactivate_locked_super(s);
- return error;
+ return ERR_PTR(error);
}
s->s_flags |= MS_ACTIVE;
- simple_set_mnt(mnt, s);
- return 0;
+ return dget(s->s_root);
}
-
-EXPORT_SYMBOL(get_sb_nodev);
+EXPORT_SYMBOL(mount_nodev);
static int compare_single(struct super_block *s, void *p)
{
return 1;
}
-int get_sb_single(struct file_system_type *fs_type,
+struct dentry *mount_single(struct file_system_type *fs_type,
int flags, void *data,
- int (*fill_super)(struct super_block *, void *, int),
- struct vfsmount *mnt)
+ int (*fill_super)(struct super_block *, void *, int))
{
struct super_block *s;
int error;
- s = sget(fs_type, compare_single, set_anon_super, NULL);
+ s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
if (IS_ERR(s))
- return PTR_ERR(s);
+ return ERR_CAST(s);
if (!s->s_root) {
- s->s_flags = flags;
error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
if (error) {
deactivate_locked_super(s);
- return error;
+ return ERR_PTR(error);
}
s->s_flags |= MS_ACTIVE;
+ } else {
+ do_remount_sb(s, flags, data, 0);
}
- do_remount_sb(s, flags, data, 0);
- simple_set_mnt(mnt, s);
- return 0;
+ return dget(s->s_root);
}
+EXPORT_SYMBOL(mount_single);
-EXPORT_SYMBOL(get_sb_single);
-
-struct vfsmount *
-vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
+struct dentry *
+mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
{
- struct vfsmount *mnt;
+ struct dentry *root;
+ struct super_block *sb;
char *secdata = NULL;
- int error;
-
- if (!type)
- return ERR_PTR(-ENODEV);
-
- error = -ENOMEM;
- mnt = alloc_vfsmnt(name);
- if (!mnt)
- goto out;
+ int error = -ENOMEM;
if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
secdata = alloc_secdata();
if (!secdata)
- goto out_mnt;
+ goto out;
error = security_sb_copy_data(data, secdata);
if (error)
goto out_free_secdata;
}
- error = type->get_sb(type, flags, name, data, mnt);
- if (error < 0)
+ root = type->mount(type, flags, name, data);
+ if (IS_ERR(root)) {
+ error = PTR_ERR(root);
goto out_free_secdata;
- BUG_ON(!mnt->mnt_sb);
+ }
+ sb = root->d_sb;
+ BUG_ON(!sb);
+ WARN_ON(!sb->s_bdi);
+ WARN_ON(sb->s_bdi == &default_backing_dev_info);
+ sb->s_flags |= MS_BORN;
- error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
- if (error)
- goto out_sb;
+ 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. This warning should be either removed or
- * converted to a BUG() in 2.6.34.
+ * violate this rule.
*/
- WARN((mnt->mnt_sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
- "negative value (%lld)\n", type->name, mnt->mnt_sb->s_maxbytes);
+ WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
+ "negative value (%lld)\n", type->name, sb->s_maxbytes);
- mnt->mnt_mountpoint = mnt->mnt_root;
- mnt->mnt_parent = mnt;
- up_write(&mnt->mnt_sb->s_umount);
+ up_write(&sb->s_umount);
free_secdata(secdata);
- return mnt;
+ return root;
out_sb:
- dput(mnt->mnt_root);
- deactivate_locked_super(mnt->mnt_sb);
+ dput(root);
+ deactivate_locked_super(sb);
out_free_secdata:
free_secdata(secdata);
-out_mnt:
- free_vfsmnt(mnt);
out:
return ERR_PTR(error);
}
-EXPORT_SYMBOL_GPL(vfs_kern_mount);
+/*
+ * This is an internal function, please use sb_end_{write,pagefault,intwrite}
+ * instead.
+ */
+void __sb_end_write(struct super_block *sb, int level)
+{
+ percpu_counter_dec(&sb->s_writers.counter[level-1]);
+ /*
+ * Make sure s_writers are updated before we wake up waiters in
+ * freeze_super().
+ */
+ smp_mb();
+ if (waitqueue_active(&sb->s_writers.wait))
+ wake_up(&sb->s_writers.wait);
+ rwsem_release(&sb->s_writers.lock_map[level-1], 1, _RET_IP_);
+}
+EXPORT_SYMBOL(__sb_end_write);
-static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
+#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 tell lockdep we are doing trylock when we
+ * already hold a freeze protection for a higher freeze level.
+ */
+static void acquire_freeze_lock(struct super_block *sb, int level, bool trylock,
+ unsigned long ip)
{
- int err;
- const char *subtype = strchr(fstype, '.');
- if (subtype) {
- subtype++;
- err = -EINVAL;
- if (!subtype[0])
- goto err;
- } else
- subtype = "";
+ int i;
+
+ if (!trylock) {
+ for (i = 0; i < level - 1; i++)
+ if (lock_is_held(&sb->s_writers.lock_map[i])) {
+ trylock = true;
+ break;
+ }
+ }
+ rwsem_acquire_read(&sb->s_writers.lock_map[level-1], 0, trylock, ip);
+}
+#endif
- mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
- err = -ENOMEM;
- if (!mnt->mnt_sb->s_subtype)
- goto err;
- return mnt;
+/*
+ * 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)
+{
+retry:
+ if (unlikely(sb->s_writers.frozen >= level)) {
+ if (!wait)
+ return 0;
+ wait_event(sb->s_writers.wait_unfrozen,
+ sb->s_writers.frozen < level);
+ }
- err:
- mntput(mnt);
- return ERR_PTR(err);
+#ifdef CONFIG_LOCKDEP
+ acquire_freeze_lock(sb, level, !wait, _RET_IP_);
+#endif
+ percpu_counter_inc(&sb->s_writers.counter[level-1]);
+ /*
+ * Make sure counter is updated before we check for frozen.
+ * freeze_super() first sets frozen and then checks the counter.
+ */
+ smp_mb();
+ if (unlikely(sb->s_writers.frozen >= level)) {
+ __sb_end_write(sb, level);
+ goto retry;
+ }
+ return 1;
}
+EXPORT_SYMBOL(__sb_start_write);
-struct vfsmount *
-do_kern_mount(const char *fstype, int flags, const char *name, void *data)
+/**
+ * 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. Caller of this function should make sure there can be no new writers
+ * of type @level before calling this function. Otherwise this function can
+ * livelock.
+ */
+static void sb_wait_write(struct super_block *sb, int level)
{
- struct file_system_type *type = get_fs_type(fstype);
- struct vfsmount *mnt;
- if (!type)
- return ERR_PTR(-ENODEV);
- mnt = vfs_kern_mount(type, flags, name, data);
- if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
- !mnt->mnt_sb->s_subtype)
- mnt = fs_set_subtype(mnt, fstype);
- put_filesystem(type);
- return mnt;
+ s64 writers;
+
+ /*
+ * We just cycle-through lockdep here so that it does not complain
+ * about returning with lock to userspace
+ */
+ rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_);
+ rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_);
+
+ do {
+ DEFINE_WAIT(wait);
+
+ /*
+ * We use a barrier in prepare_to_wait() to separate setting
+ * of frozen and checking of the counter
+ */
+ prepare_to_wait(&sb->s_writers.wait, &wait,
+ TASK_UNINTERRUPTIBLE);
+
+ writers = percpu_counter_sum(&sb->s_writers.counter[level-1]);
+ if (writers)
+ schedule();
+
+ finish_wait(&sb->s_writers.wait, &wait);
+ } while (writers);
}
-EXPORT_SYMBOL_GPL(do_kern_mount);
-struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
+/**
+ * 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)
{
- return vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
+ 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 & MS_BORN)) {
+ up_write(&sb->s_umount);
+ return 0; /* sic - it's "nothing to do" */
+ }
+
+ if (sb->s_flags & MS_RDONLY) {
+ /* Nothing to do really... */
+ sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+ up_write(&sb->s_umount);
+ return 0;
+ }
+
+ /* From now on, no new normal writers can start */
+ sb->s_writers.frozen = SB_FREEZE_WRITE;
+ smp_wmb();
+
+ /* Release s_umount to preserve sb_start_write -> s_umount ordering */
+ up_write(&sb->s_umount);
+
+ sb_wait_write(sb, SB_FREEZE_WRITE);
+
+ /* Now we go and block page faults... */
+ down_write(&sb->s_umount);
+ sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
+ smp_wmb();
+
+ 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;
+ smp_wmb();
+ 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;
+ smp_wmb();
+ wake_up(&sb->s_writers.wait_unfrozen);
+ deactivate_locked_super(sb);
+ return ret;
+ }
+ }
+ /*
+ * This is just for debugging purposes so that fs can warn if it
+ * sees write activity when frozen is set to SB_FREEZE_COMPLETE.
+ */
+ sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+ up_write(&sb->s_umount);
+ return 0;
}
+EXPORT_SYMBOL(freeze_super);
-EXPORT_SYMBOL_GPL(kern_mount_data);
+/**
+ * thaw_super -- unlock filesystem
+ * @sb: the super to thaw
+ *
+ * Unlocks the filesystem and marks it writeable again after freeze_super().
+ */
+int thaw_super(struct super_block *sb)
+{
+ int error;
+
+ down_write(&sb->s_umount);
+ if (sb->s_writers.frozen == SB_UNFROZEN) {
+ up_write(&sb->s_umount);
+ return -EINVAL;
+ }
+
+ if (sb->s_flags & MS_RDONLY)
+ goto out;
+
+ if (sb->s_op->unfreeze_fs) {
+ error = sb->s_op->unfreeze_fs(sb);
+ if (error) {
+ printk(KERN_ERR
+ "VFS:Filesystem thaw failed\n");
+ up_write(&sb->s_umount);
+ return error;
+ }
+ }
+
+out:
+ sb->s_writers.frozen = SB_UNFROZEN;
+ smp_wmb();
+ wake_up(&sb->s_writers.wait_unfrozen);
+ deactivate_locked_super(sb);
+
+ return 0;
+}
+EXPORT_SYMBOL(thaw_super);