3 files changed, 120 insertions, 61 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 22506eb4a58e..9cf4b926f8e4 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -230,43 +230,54 @@ struct super_block *freeze_bdev(struct block_device *bdev)
         int error = 0;
 
         mutex_lock(&bdev->bd_fsfreeze_mutex);
-        if (bdev->bd_fsfreeze_count > 0) {
-                bdev->bd_fsfreeze_count++;
+        if (++bdev->bd_fsfreeze_count > 1) {
+                /*
+                 * We don't even need to grab a reference - the first call
+                 * to freeze_bdev grab an active reference and only the last
+                 * thaw_bdev drops it.
+                 */
                 sb = get_super(bdev);
+                drop_super(sb);
                 mutex_unlock(&bdev->bd_fsfreeze_mutex);
                 return sb;
         }
-        bdev->bd_fsfreeze_count++;
-
-        sb = get_super(bdev);
-        if (sb && !(sb->s_flags & MS_RDONLY)) {
-                sb->s_frozen = SB_FREEZE_WRITE;
-                smp_wmb();
-
-                sync_filesystem(sb);
-
-                sb->s_frozen = SB_FREEZE_TRANS;
-                smp_wmb();
-
-                sync_blockdev(sb->s_bdev);
-
-                if (sb->s_op->freeze_fs) {
-                        error = sb->s_op->freeze_fs(sb);
-                        if (error) {
-                                printk(KERN_ERR
-                                        "VFS:Filesystem freeze failed\n");
-                                sb->s_frozen = SB_UNFROZEN;
-                                drop_super(sb);
-                                bdev->bd_fsfreeze_count--;
-                                mutex_unlock(&bdev->bd_fsfreeze_mutex);
-                                return ERR_PTR(error);
-                        }
+
+        sb = get_active_super(bdev);
+        if (!sb)
+                goto out;
+        if (sb->s_flags & MS_RDONLY) {
+                deactivate_locked_super(sb);
+                mutex_unlock(&bdev->bd_fsfreeze_mutex);
+                return sb;
+        }
+
+        sb->s_frozen = SB_FREEZE_WRITE;
+        smp_wmb();
+
+        sync_filesystem(sb);
+
+        sb->s_frozen = SB_FREEZE_TRANS;
+        smp_wmb();
+
+        sync_blockdev(sb->s_bdev);
+
+        if (sb->s_op->freeze_fs) {
+                error = sb->s_op->freeze_fs(sb);
+                if (error) {
+                        printk(KERN_ERR
+                                "VFS:Filesystem freeze failed\n");
+                        sb->s_frozen = SB_UNFROZEN;
+                        deactivate_locked_super(sb);
+                        bdev->bd_fsfreeze_count--;
+                        mutex_unlock(&bdev->bd_fsfreeze_mutex);
+                        return ERR_PTR(error);
                 }
         }
+        up_write(&sb->s_umount);
 
+ out:
         sync_blockdev(bdev);
         mutex_unlock(&bdev->bd_fsfreeze_mutex);
-
         return sb;      /* thaw_bdev releases s->s_umount */
 }
 EXPORT_SYMBOL(freeze_bdev);
@@ -280,43 +291,44 @@ EXPORT_SYMBOL(freeze_bdev);
  */
 int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 {
-        int error = 0;
+        int error = -EINVAL;
 
         mutex_lock(&bdev->bd_fsfreeze_mutex);
-        if (!bdev->bd_fsfreeze_count) {
-                mutex_unlock(&bdev->bd_fsfreeze_mutex);
-                return -EINVAL;
-        }
-
-        bdev->bd_fsfreeze_count--;
-        if (bdev->bd_fsfreeze_count > 0) {
-                if (sb)
-                        drop_super(sb);
-                mutex_unlock(&bdev->bd_fsfreeze_mutex);
-                return 0;
-        }
-
-        if (sb) {
-                BUG_ON(sb->s_bdev != bdev);
-                if (!(sb->s_flags & MS_RDONLY)) {
-                        if (sb->s_op->unfreeze_fs) {
-                                error = sb->s_op->unfreeze_fs(sb);
-                                if (error) {
-                                        printk(KERN_ERR
-                                                "VFS:Filesystem thaw failed\n");
-                                        sb->s_frozen = SB_FREEZE_TRANS;
-                                        bdev->bd_fsfreeze_count++;
-                                        mutex_unlock(&bdev->bd_fsfreeze_mutex);
-                                        return error;
-                                }
-                        }
-                        sb->s_frozen = SB_UNFROZEN;
-                        smp_wmb();
-                        wake_up(&sb->s_wait_unfrozen);
+        if (!bdev->bd_fsfreeze_count)
+                goto out_unlock;
+
+        error = 0;
+        if (--bdev->bd_fsfreeze_count > 0)
+                goto out_unlock;
+
+        if (!sb)
+                goto out_unlock;
+
+        BUG_ON(sb->s_bdev != bdev);
+        down_write(&sb->s_umount);
+        if (sb->s_flags & MS_RDONLY)
+                goto out_deactivate;
+
+        if (sb->s_op->unfreeze_fs) {
+                error = sb->s_op->unfreeze_fs(sb);
+                if (error) {
+                        printk(KERN_ERR
+                                "VFS:Filesystem thaw failed\n");
+                        sb->s_frozen = SB_FREEZE_TRANS;
+                        bdev->bd_fsfreeze_count++;
+                        mutex_unlock(&bdev->bd_fsfreeze_mutex);
+                        return error;
                 }
-                drop_super(sb);
         }
 
+        sb->s_frozen = SB_UNFROZEN;
+        smp_wmb();
+        wake_up(&sb->s_wait_unfrozen);
+
+out_deactivate:
+        if (sb)
+                deactivate_locked_super(sb);
+out_unlock:
         mutex_unlock(&bdev->bd_fsfreeze_mutex);
         return 0;
 }
diff --git a/fs/super.c b/fs/super.c
index 1cb26a3e3df0..19eb70b374bc 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -465,6 +465,48 @@ rescan:
 }
 
 EXPORT_SYMBOL(get_super);
+
+/**
+ * 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 and s_umount held exclusively or %NULL if none was found.
+ */
+struct super_block *get_active_super(struct block_device *bdev)
+{
+        struct super_block *sb;
+
+        if (!bdev)
+                return NULL;
+
+        spin_lock(&sb_lock);
+        list_for_each_entry(sb, &super_blocks, s_list) {
+                if (sb->s_bdev != bdev)
+                        continue;
+
+                sb->s_count++;
+                spin_unlock(&sb_lock);
+                down_write(&sb->s_umount);
+                if (sb->s_root) {
+                        spin_lock(&sb_lock);
+                        if (sb->s_count > S_BIAS) {
+                                atomic_inc(&sb->s_active);
+                                sb->s_count--;
+                                spin_unlock(&sb_lock);
+                                return sb;
+                        }
+                        spin_unlock(&sb_lock);
+                }
+                up_write(&sb->s_umount);
+                put_super(sb);
+                yield();
+                spin_lock(&sb_lock);
+        }
+        spin_unlock(&sb_lock);
+        return NULL;
+}
  
 struct super_block * user_get_super(dev_t dev)
 {
@@ -527,11 +569,15 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
 {
         int retval;
         int remount_rw;
-        
+
+        if (sb->s_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);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 72dfbd423974..502d96ef345d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2334,6 +2334,7 @@ extern void get_filesystem(struct file_system_type *fs);
 extern void put_filesystem(struct file_system_type *fs);
 extern struct file_system_type *get_fs_type(const char *name);
 extern struct super_block *get_super(struct block_device *);
+extern struct super_block *get_active_super(struct block_device *bdev);
 extern struct super_block *user_get_super(dev_t);
 extern void drop_super(struct super_block *sb);