1 files changed, 45 insertions, 25 deletions

diff --git a/fs/super.c b/fs/super.c
index afd0f1ad45e0..de41e1e46f09 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -136,12 +136,13 @@ static struct super_block *alloc_super(struct file_system_type *type)
                 INIT_LIST_HEAD(&s->s_files);
 #endif
                 s->s_bdi = &default_backing_dev_info;
-                INIT_LIST_HEAD(&s->s_instances);
+                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);
@@ -200,6 +201,7 @@ static inline void destroy_super(struct super_block *s)
         free_percpu(s->s_files);
 #endif
         security_sb_free(s);
+        WARN_ON(!list_empty(&s->s_mounts));
         kfree(s->s_subtype);
         kfree(s->s_options);
         kfree(s);
@@ -210,7 +212,7 @@ static inline void destroy_super(struct super_block *s)
 /*
  * Drop a superblock's refcount.  The caller must hold sb_lock.
  */
-void __put_super(struct super_block *sb)
+static void __put_super(struct super_block *sb)
 {
         if (!--sb->s_count) {
                 list_del_init(&sb->s_list);
@@ -225,7 +227,7 @@ void __put_super(struct super_block *sb)
  *      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);
@@ -328,7 +330,7 @@ static int grab_super(struct super_block *s) __releases(sb_lock)
 bool grab_super_passive(struct super_block *sb)
 {
         spin_lock(&sb_lock);
-        if (list_empty(&sb->s_instances)) {
+        if (hlist_unhashed(&sb->s_instances)) {
                 spin_unlock(&sb_lock);
                 return false;
         }
@@ -337,7 +339,7 @@ bool grab_super_passive(struct super_block *sb)
         spin_unlock(&sb_lock);
 
         if (down_read_trylock(&sb->s_umount)) {
-                if (sb->s_root)
+                if (sb->s_root && (sb->s_flags & MS_BORN))
                         return true;
                 up_read(&sb->s_umount);
         }
@@ -400,7 +402,7 @@ void generic_shutdown_super(struct super_block *sb)
         }
         spin_lock(&sb_lock);
         /* should be initialized for __put_super_and_need_restart() */
-        list_del_init(&sb->s_instances);
+        hlist_del_init(&sb->s_instances);
         spin_unlock(&sb_lock);
         up_write(&sb->s_umount);
 }
@@ -420,13 +422,14 @@ struct super_block *sget(struct file_system_type *type,
                         void *data)
 {
         struct super_block *s = NULL;
+        struct hlist_node *node;
         struct super_block *old;
         int err;
 
 retry:
         spin_lock(&sb_lock);
         if (test) {
-                list_for_each_entry(old, &type->fs_supers, s_instances) {
+                hlist_for_each_entry(old, node, &type->fs_supers, s_instances) {
                         if (!test(old, data))
                                 continue;
                         if (!grab_super(old))
@@ -462,7 +465,7 @@ 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);
@@ -497,14 +500,14 @@ void sync_supers(void)
 
         spin_lock(&sb_lock);
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (list_empty(&sb->s_instances))
+                if (hlist_unhashed(&sb->s_instances))
                         continue;
                 if (sb->s_op->write_super && sb->s_dirt) {
                         sb->s_count++;
                         spin_unlock(&sb_lock);
 
                         down_read(&sb->s_umount);
-                        if (sb->s_root && sb->s_dirt)
+                        if (sb->s_root && sb->s_dirt && (sb->s_flags & MS_BORN))
                                 sb->s_op->write_super(sb);
                         up_read(&sb->s_umount);
 
@@ -533,13 +536,13 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 
         spin_lock(&sb_lock);
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (list_empty(&sb->s_instances))
+                if (hlist_unhashed(&sb->s_instances))
                         continue;
                 sb->s_count++;
                 spin_unlock(&sb_lock);
 
                 down_read(&sb->s_umount);
-                if (sb->s_root)
+                if (sb->s_root && (sb->s_flags & MS_BORN))
                         f(sb, arg);
                 up_read(&sb->s_umount);
 
@@ -566,14 +569,15 @@ void iterate_supers_type(struct file_system_type *type,
         void (*f)(struct super_block *, void *), void *arg)
 {
         struct super_block *sb, *p = NULL;
+        struct hlist_node *node;
 
         spin_lock(&sb_lock);
-        list_for_each_entry(sb, &type->fs_supers, s_instances) {
+        hlist_for_each_entry(sb, node, &type->fs_supers, s_instances) {
                 sb->s_count++;
                 spin_unlock(&sb_lock);
 
                 down_read(&sb->s_umount);
-                if (sb->s_root)
+                if (sb->s_root && (sb->s_flags & MS_BORN))
                         f(sb, arg);
                 up_read(&sb->s_umount);
 
@@ -607,14 +611,14 @@ struct super_block *get_super(struct block_device *bdev)
         spin_lock(&sb_lock);
 rescan:
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (list_empty(&sb->s_instances))
+                if (hlist_unhashed(&sb->s_instances))
                         continue;
                 if (sb->s_bdev == bdev) {
                         sb->s_count++;
                         spin_unlock(&sb_lock);
                         down_read(&sb->s_umount);
                         /* still alive? */
-                        if (sb->s_root)
+                        if (sb->s_root && (sb->s_flags & MS_BORN))
                                 return sb;
                         up_read(&sb->s_umount);
                         /* nope, got unmounted */
@@ -647,7 +651,7 @@ struct super_block *get_active_super(struct block_device *bdev)
 restart:
         spin_lock(&sb_lock);
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (list_empty(&sb->s_instances))
+                if (hlist_unhashed(&sb->s_instances))
                         continue;
                 if (sb->s_bdev == bdev) {
                         if (grab_super(sb)) /* drops sb_lock */
@@ -667,14 +671,14 @@ struct super_block *user_get_super(dev_t dev)
         spin_lock(&sb_lock);
 rescan:
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (list_empty(&sb->s_instances))
+                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)
+                        if (sb->s_root && (sb->s_flags & MS_BORN))
                                 return sb;
                         up_read(&sb->s_umount);
                         /* nope, got unmounted */
@@ -719,23 +723,29 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
         /* If we are remounting RDONLY and current sb is read/write,
            make sure there are no rw files opened */
         if (remount_ro) {
-                if (force)
+                if (force) {
                         mark_files_ro(sb);
-                else if (!fs_may_remount_ro(sb))
-                        return -EBUSY;
+                } else {
+                        retval = sb_prepare_remount_readonly(sb);
+                        if (retval)
+                                return retval;
+                }
         }
 
         if (sb->s_op->remount_fs) {
                 retval = sb->s_op->remount_fs(sb, &flags, data);
                 if (retval) {
                         if (!force)
-                                return retval;
+                                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);
+        /* 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
@@ -748,6 +758,10 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
         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)
@@ -756,12 +770,13 @@ static void do_emergency_remount(struct work_struct *work)
 
         spin_lock(&sb_lock);
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (list_empty(&sb->s_instances))
+                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)) {
                         /*
                          * What lock protects sb->s_flags??
                          */
@@ -1144,6 +1159,11 @@ int freeze_super(struct super_block *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) {
                 sb->s_frozen = SB_FREEZE_TRANS;
                 smp_wmb();