Patch "dm mpath: avoid that path removal can trigger an infinite loop" has been added to the 4.11-stable tree

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

dm mpath: avoid that path removal can trigger an infinite loop

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-avoid-that-path-removal-can-trigger-an-infinite-loop.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 <[email protected]> know about it.

From: Bart Van Assche <[email protected]>
Date: Thu, 27 Apr 2017 10:11:15 -0700
Subject: dm mpath: avoid that path removal can trigger an infinite loop

From: Bart Van Assche <[email protected]>

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.

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

@@ -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;

Patches currently in stable-queue which might be from [email protected] 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