diff --git a/drivers/md/md.h b/drivers/md/md.h
index 37e7c17..e41559d 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -391,6 +391,7 @@
 	 *   rdev superblocks, events
 	 *   clearing MD_CHANGE_*
 	 *   in_sync - and related safemode and MD_CHANGE changes
+	 *   pers (also protected by reconfig_mutex and pending IO).
 	 */
 	spinlock_t			lock;
 	wait_queue_head_t		sb_wait;	/* for waiting on superblock updates */