freeze_bdev: kill bd_mount_sem

Now that we have the freeze count there is not much reason for bd_mount_sem
anymore.  The actual freeze/thaw operations are serialized using the
bd_fsfreeze_mutex, and the only other place we take bd_mount_sem is
get_sb_bdev which tries to prevent mounting a filesystem while the block
device is frozen.  Instead of add a check for bd_fsfreeze_count and
return -EBUSY if a filesystem is frozen.  While that is a change in user
visible behaviour a failing mount is much better for this case rather
than having the mount process stuck uninterruptible for a long time.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 8 insertions, 9 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 5d1ed50bd46c..22506eb4a58e 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -216,8 +216,6 @@ EXPORT_SYMBOL(fsync_bdev);
  * freeze_bdev  --  lock a filesystem and force it into a consistent state
  * @bdev:       blockdevice to lock
  *
- * This takes the block device bd_mount_sem to make sure no new mounts
- * happen on bdev until thaw_bdev() is called.
  * If a superblock is found on this device, we take the s_umount semaphore
  * on it to make sure nobody unmounts until the snapshot creation is done.
  * The reference counter (bd_fsfreeze_count) guarantees that only the last
@@ -240,7 +238,6 @@ struct super_block *freeze_bdev(struct block_device *bdev)
         }
         bdev->bd_fsfreeze_count++;
 
-        down(&bdev->bd_mount_sem);
         sb = get_super(bdev);
         if (sb && !(sb->s_flags & MS_RDONLY)) {
                 sb->s_frozen = SB_FREEZE_WRITE;
@@ -260,7 +257,6 @@ struct super_block *freeze_bdev(struct block_device *bdev)
                                         "VFS:Filesystem freeze failed\n");
                                 sb->s_frozen = SB_UNFROZEN;
                                 drop_super(sb);
-                                up(&bdev->bd_mount_sem);
                                 bdev->bd_fsfreeze_count--;
                                 mutex_unlock(&bdev->bd_fsfreeze_mutex);
                                 return ERR_PTR(error);
@@ -271,7 +267,7 @@ struct super_block *freeze_bdev(struct block_device *bdev)
         sync_blockdev(bdev);
         mutex_unlock(&bdev->bd_fsfreeze_mutex);
 
-        return sb;      /* thaw_bdev releases s->s_umount and bd_mount_sem */
+        return sb;      /* thaw_bdev releases s->s_umount */
 }
 EXPORT_SYMBOL(freeze_bdev);
 
@@ -321,7 +317,6 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
                 drop_super(sb);
         }
 
-        up(&bdev->bd_mount_sem);
         mutex_unlock(&bdev->bd_fsfreeze_mutex);
         return 0;
 }
@@ -430,7 +425,6 @@ static void init_once(void *foo)
 
         memset(bdev, 0, sizeof(*bdev));
         mutex_init(&bdev->bd_mutex);
-        sema_init(&bdev->bd_mount_sem, 1);
         INIT_LIST_HEAD(&bdev->bd_inodes);
         INIT_LIST_HEAD(&bdev->bd_list);
 #ifdef CONFIG_SYSFS
diff --git a/fs/super.c b/fs/super.c
index 4906e2d8f400..1cb26a3e3df0 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -743,9 +743,14 @@ int get_sb_bdev(struct file_system_type *fs_type,
          * will protect the lockfs code from trying to start a snapshot
          * while we are mounting
          */
-        down(&bdev->bd_mount_sem);
+        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, bdev);
-        up(&bdev->bd_mount_sem);
+        mutex_unlock(&bdev->bd_fsfreeze_mutex);
         if (IS_ERR(s))
                 goto error_s;