1 files changed, 6 insertions, 1 deletions

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 3c1f7310421e..5139a833f721 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -96,7 +96,12 @@ struct btrfs_fs_devices {
         u64 rw_devices;
         u64 total_rw_bytes;
         struct block_device *latest_bdev;
-        /* all of the devices in the FS */
+
+        /* 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
+         */
+        struct mutex device_list_mutex;
         struct list_head devices;
 
         /* devices not currently being allocated */