diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 1170909..caa860a 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -544,6 +544,7 @@
 	/* for block groups in our same type */
 	struct list_head block_groups;
 	spinlock_t lock;
+	struct rw_semaphore groups_sem;
 };
 
 struct btrfs_free_space {