From 1f97be20ccf457542fe932920f3d4a6aaad13a50 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Fri, 28 Nov 2008 13:32:07 +0900
Subject: [PATCH] --- yaml --- r: 123291 b: refs/heads/master c:
 a185eb4bc84155fff35b602ce99602c010de9634 h: refs/heads/master i:   123289:
 2fdb69d283e0c607518812c1cc6dcd9cc22376dc   123287:
 43b5b187ccf4c4fdf5951874d29012e28587e88f v: v3

---
 [refs]                    |  2 +-
 trunk/block/blk-barrier.c | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/[refs] b/[refs]
index c501ec0c4c6a..e07cdcd4af2d 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 58eea927d2de43dc6f03d1ba2c46e55854b31540
+refs/heads/master: a185eb4bc84155fff35b602ce99602c010de9634
diff --git a/trunk/block/blk-barrier.c b/trunk/block/blk-barrier.c
index c63044e9c4c0..8eba4e43bb0c 100644
--- a/trunk/block/blk-barrier.c
+++ b/trunk/block/blk-barrier.c
@@ -166,9 +166,21 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
 	 * For an empty barrier, there's no actual BAR request, which
 	 * in turn makes POSTFLUSH unnecessary.  Mask them off.
 	 */
-	if (!rq->hard_nr_sectors)
+	if (!rq->hard_nr_sectors) {
 		q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
 				QUEUE_ORDERED_DO_POSTFLUSH);
+		/*
+		 * Empty barrier on a write-through device w/ ordered
+		 * tag has no command to issue and without any command
+		 * to issue, ordering by tag can't be used.  Drain
+		 * instead.
+		 */
+		if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
+		    !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
+			q->ordered &= ~QUEUE_ORDERED_BY_TAG;
+			q->ordered |= QUEUE_ORDERED_BY_DRAIN;
+		}
+	}
 
 	/* stash away the original request */
 	elv_dequeue_request(q, rq);