[PATCH v4 6/6] dm rq: Avoid that request processing stalls sporadically

[Bart Van Assche]

While running the srp-test software I noticed that request
processing stalls sporadically at the beginning of a test, namely
when mkfs is run against a dm-mpath device. Every time when that
happened the following command was sufficient to resume request
processing:

    echo run >/sys/kernel/debug/block/dm-0/state

This patch avoids that such request processing stalls occur. The
test I ran is as follows:

    while srp-test/run_tests -d -r 30 -t 02-mq; do :; done

Signed-off-by: Bart Van Assche <bart.vanass...@sandisk.com>
Cc: Mike Snitzer <snit...@redhat.com>
Cc: dm-de...@redhat.com
---
 drivers/md/dm-rq.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 6886bf160fb2..d19af1d21f4c 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -755,6 +755,7 @@ static int dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
                /* Undo dm_start_request() before requeuing */
                rq_end_stats(md, rq);
                rq_completed(md, rq_data_dir(rq), false);
+               blk_mq_delay_run_hw_queue(hctx, 100/*ms*/);
                return BLK_MQ_RQ_QUEUE_BUSY;
        }
 
-- 
2.12.0