[PATCH] honor hard barrier in deadline

Previously, we only honored barriers wrt merging. Really honor them now,
move all pending requests to dispatch list and add the hard barrier at
the back.

drivers/block/deadline-iosched.c

@@ -608,6 +608,12 @@ deadline_insert_request(request_queue_t *q, struct request *rq,
 	if (unlikely(rq->flags & REQ_HARDBARRIER)) {
 		DL_INVALIDATE_HASH(dd);
 		q->last_merge = NULL;
+
+		while (deadline_dispatch_requests(dd))
+			;
+
+		list_add_tail(&rq->queuelist, dd->dispatch);
+		return;
 	}
 
 	if (unlikely(!blk_fs_request(rq))) {