diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index 8c2cb87bccc5d..c1f9cc728c2db 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -553,6 +553,9 @@ static int slow_eval_unknown_fn(struct subchannel_id schid, void *data)
 		default:
 			rc = 0;
 		}
+		/* Allow scheduling here since the containing loop might
+		 * take a while.  */
+		cond_resched();
 	}
 	return rc;
 }