Patch "dm mpath: requeue after a small delay if blk_get_request() fails" has been added to the 4.11-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    dm mpath: requeue after a small delay if blk_get_request() fails

to the 4.11-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     dm-mpath-requeue-after-a-small-delay-if-blk_get_request-fails.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 06eb061f48594aa369f6e852b352410298b317a8 Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bart.vanassche@sandisk.com>
Date: Fri, 7 Apr 2017 16:50:44 -0700
Subject: dm mpath: requeue after a small delay if blk_get_request() fails

From: Bart Van Assche <bart.vanassche@sandisk.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@sandisk.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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);
 }


Patches currently in stable-queue which might be from bart.vanassche@sandisk.com are

queue-4.11/dm-mpath-requeue-after-a-small-delay-if-blk_get_request-fails.patch
queue-4.11/dm-mpath-avoid-that-path-removal-can-trigger-an-infinite-loop.patch
queue-4.11/dm-mpath-split-and-rename-activate_path-to-prepare-for-its-expanded-use.patch
queue-4.11/dm-mpath-delay-requeuing-while-path-initialization-is-in-progress.patch