On 04/26/2017 08:37 PM, Bart Van Assche wrote:
> 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 patch 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 because in these cases immediate requeuing is
> inappropriate.
>
> Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> ---
> drivers/md/dm-mpath.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index 909098e18643..6d4333fdddf5 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -490,6 +490,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
> 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? */
> @@ -512,13 +513,19 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
> 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 */
> - return r;
> + pr_debug("blk_get_request() returned %ld%s - requeuing\n",
> + PTR_ERR(clone), blk_queue_dying(q) ?
> + " (path offline)" : "");
> + if (blk_queue_dying(q)) {
> + atomic_inc(&m->pg_init_in_progress);
> + activate_path(pgpath);
> + return DM_MAPIO_REQUEUE;
> + }
> + return DM_MAPIO_DELAY_REQUEUE;
> }
> clone->bio = clone->biotail = NULL;
> clone->rq_disk = bdev->bd_disk;
>
At the very least this does warrant some inline comments.
Why do we call activate_path() here, seeing that the queue is dying?
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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