Btrfs: pause the space balance when remounting to R/O

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index a4807ce..f0857e0 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1263,6 +1263,7 @@
 
 		btrfs_dev_replace_suspend_for_unmount(fs_info);
 		btrfs_scrub_cancel(fs_info);
+		btrfs_pause_balance(fs_info);
 
 		ret = btrfs_commit_super(root);
 		if (ret)