[PATCH 4.1 050/123] Revert "dm: only run the queue on completion if congested or no requests pending"

[Greg Kroah-Hartman]

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Snitzer <snitzer@xxxxxxxxxx>

commit 621739b00e16ca2d80411dc9b111cb15b91f3ba9 upstream.

This reverts commit 9a0e609e3fd8a95c96629b9fbde6b8c5b9a1456a.
(Resolved a conflict during revert due to commit bfebd1cdb4 that came
after)

This revert is motivated by a couple failure reports on request-based DM
multipath testbeds:
1) Netapp reported that their multipath fault injection test under heavy
   IO load can stall longer than 300 seconds.
2) IBM reported elevated lock contention in their testbed (likely due to
   increased back pressure due to IO not being dispatched as quickly):
   https://www.redhat.com/archives/dm-devel/2015-July/msg00057.html

Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/md/dm.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1053,13 +1053,10 @@ static struct dm_rq_target_io *tio_from_
  */
 static void rq_completed(struct mapped_device *md, int rw, bool run_queue)
 {
-	int nr_requests_pending;
-
 	atomic_dec(&md->pending[rw]);
 
 	/* nudge anyone waiting on suspend queue */
-	nr_requests_pending = md_in_flight(md);
-	if (!nr_requests_pending)
+	if (!md_in_flight(md))
 		wake_up(&md->wait);
 
 	/*
@@ -1071,8 +1068,7 @@ static void rq_completed(struct mapped_d
 	if (run_queue) {
 		if (md->queue->mq_ops)
 			blk_mq_run_hw_queues(md->queue, true);
-		else if (!nr_requests_pending ||
-			 (nr_requests_pending >= md->queue->nr_congestion_on))
+		else
 			blk_run_queue_async(md->queue);
 	}
 


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