linux-kernel - [PATCH 4.11 027/197] dm mpath: requeue after a small delay if blk_get

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Message-Id: <20170523200823.835284602@linuxfoundation.org>
Date:   Tue, 23 May 2017 22:06:28 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 4.11 027/197] dm mpath: requeue after a small delay if blk_get_request() fails

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

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

From: Bart Van Assche <bart.vanassche@...disk.com>

commit 06eb061f48594aa369f6e852b352410298b317a8 upstream.

If blk_get_request() returns ENODEV then multipath_clone_and_map()
causes a request to be requeued immediately. This can cause a kworker
thread to spend 100% of the CPU time of a single core in
__blk_mq_run_hw_queue() and also can cause device removal to never
finish.

Avoid this by only requeuing after a delay if blk_get_request() fails.
Additionally, reduce the requeue delay.

Signed-off-by: Bart Van Assche <bart.vanassche@...disk.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/dm-mpath.c |    5 ++---
 drivers/md/dm-rq.c    |    2 +-
 2 files changed, 3 insertions(+), 4 deletions(-)

--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -484,7 +484,6 @@ static int multipath_clone_and_map(struc
 				   struct request **__clone)
 {
 	struct multipath *m = ti->private;
-	int r = DM_MAPIO_REQUEUE;
 	size_t nr_bytes = blk_rq_bytes(rq);
 	struct pgpath *pgpath;
 	struct block_device *bdev;
@@ -503,7 +502,7 @@ static int multipath_clone_and_map(struc
 	} else if (test_bit(MPATHF_QUEUE_IO, &m->flags) ||
 		   test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags)) {
 		pg_init_all_paths(m);
-		return r;
+		return DM_MAPIO_REQUEUE;
 	}
 
 	memset(mpio, 0, sizeof(*mpio));
@@ -517,7 +516,7 @@ static int multipath_clone_and_map(struc
 			GFP_ATOMIC);
 	if (IS_ERR(clone)) {
 		/* EBUSY, ENODEV or EWOULDBLOCK: requeue */
-		return r;
+		return DM_MAPIO_DELAY_REQUEUE;
 	}
 	clone->bio = clone->biotail = NULL;
 	clone->rq_disk = bdev->bd_disk;
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -280,7 +280,7 @@ static void dm_requeue_original_request(
 	if (!rq->q->mq_ops)
 		dm_old_requeue_request(rq);
 	else
-		dm_mq_delay_requeue_request(rq, delay_requeue ? 5000 : 0);
+		dm_mq_delay_requeue_request(rq, delay_requeue ? 100/*ms*/ : 0);
 
 	rq_completed(md, rw, false);
 }