Btrfs: remove scrub_super_lock holding in btrfs_sync_log()

Originally, we introduced scrub_super_lock to synchronize
tree log code with scrubbing super.

However we can replace scrub_super_lock with device_list_mutex,
because writing super will hold this mutex, this will reduce an extra
lock holding when writing supers in sync log code.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index b72f540c8b2..49e0ff01143 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -132,7 +132,9 @@ struct btrfs_fs_devices {
 
 	/* all of the devices in the FS, protected by a mutex
 	 * so we can safely walk it to write out the supers without
-	 * worrying about add/remove by the multi-device code
+	 * worrying about add/remove by the multi-device code.
+	 * Scrubbing super can kick off supers writing by holding
+	 * this mutex lock.
 	 */
 	struct mutex device_list_mutex;
 	struct list_head devices;