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FAILED: patch "[PATCH] dm mpath: requeue after a small delay if blk_get_request()" failed to apply to 4.9-stable tree

PATCH [email protected] 1 participant 1 message May 22, 2017

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The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

Quoted 1 line

From 06eb061f48594aa369f6e852b352410298b317a8 Mon Sep 17 00:00:00 2001

From: Bart Van Assche <[email protected]>
Date: Fri, 7 Apr 2017 16:50:44 -0700
Subject: [PATCH] dm mpath: requeue after a small delay if blk_get_request()
fails

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.

Cc [email protected] # 4.9+
Signed-off-by Bart Van Assche <[email protected]>
Signed-off-by Mike Snitzer <[email protected]>
drivers/md/dm-mpath.c +2 -3
index 7f223dbed49f..a4cc4d42117b 100644
@@ -484,7 +484,6 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
 				   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(struct dm_target *ti, struct request *rq,
 	} 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(struct dm_target *ti, struct request *rq,
 			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;
drivers/md/dm-rq.c +1 -1
index 28955b94d2b2..90756a56c4d3 100644
@@ -280,7 +280,7 @@ static void dm_requeue_original_request(struct dm_rq_target_io *tio, bool delay_
 	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);
 }