linux-kernel - [PATCH 4.11 029/197] dm mpath: avoid that path removal can trigger an infinite loop

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Message-Id: <20170523200824.185443353@linuxfoundation.org>
Date:   Tue, 23 May 2017 22:06:30 +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>,
        Hannes Reinecke <hare@...e.com>,
        Christoph Hellwig <hch@....de>,
        Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 4.11 029/197] dm mpath: avoid that path removal can trigger an infinite loop

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

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

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

commit 7083abbbfc4fa706ff72d27d33a5214881979336 upstream.

If blk_get_request() fails, check whether the failure is due to a path
being removed.  If that is the case, fail the path by triggering a call
to fail_path().  This avoids that the following scenario can be
encountered while removing paths:
* CPU usage of a kworker thread jumps to 100%.
* Removing the DM device becomes impossible.

Delay requeueing if blk_get_request() returns -EBUSY or -EWOULDBLOCK,
and the queue is not dying, because in these cases immediate requeuing
is inappropriate.

Signed-off-by: Bart Van Assche <bart.vanassche@...disk.com>
Cc: Hannes Reinecke <hare@...e.com>
Cc: Christoph Hellwig <hch@....de>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/dm-mpath.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -489,6 +489,7 @@ static int multipath_clone_and_map(struc
 	struct pgpath *pgpath;
 	struct block_device *bdev;
 	struct dm_mpath_io *mpio = get_mpio(map_context);
+	struct request_queue *q;
 	struct request *clone;
 
 	/* Do we need to select a new pgpath? */
@@ -511,12 +512,18 @@ static int multipath_clone_and_map(struc
 	mpio->nr_bytes = nr_bytes;
 
 	bdev = pgpath->path.dev->bdev;
-
-	clone = blk_get_request(bdev_get_queue(bdev),
-			rq->cmd_flags | REQ_NOMERGE,
-			GFP_ATOMIC);
+	q = bdev_get_queue(bdev);
+	clone = blk_get_request(q, rq->cmd_flags | REQ_NOMERGE, GFP_ATOMIC);
 	if (IS_ERR(clone)) {
 		/* EBUSY, ENODEV or EWOULDBLOCK: requeue */
+		bool queue_dying = blk_queue_dying(q);
+		DMERR_LIMIT("blk_get_request() returned %ld%s - requeuing",
+			    PTR_ERR(clone), queue_dying ? " (path offline)" : "");
+		if (queue_dying) {
+			atomic_inc(&m->pg_init_in_progress);
+			activate_or_offline_path(pgpath);
+			return DM_MAPIO_REQUEUE;
+		}
 		return DM_MAPIO_DELAY_REQUEUE;
 	}
 	clone->bio = clone->biotail = NULL;