Re: [PATCH 10/24] scsi-multipath: add scsi_mpath_{start,end}_request()

[Benjamin Marzinski <bmarzins@redhat.com>]

On Wed, Feb 25, 2026 at 03:36:13PM +0000, John Garry wrote:
> Add scsi_mpath_{start,end}_request() to handle updating private multipath
> request data, like nvme_mpath_{start,end}_request().
> 
> Since we may need to update mpath_disk data, add a callbacks in
> scsi_driver to actually do this work for the scsi driver.
> 
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
>  drivers/scsi/scsi_lib.c       |  4 ++++
>  include/scsi/scsi_driver.h    |  2 ++
>  include/scsi/scsi_multipath.h | 24 ++++++++++++++++++++++++
>  3 files changed, 30 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 7ed0defc8161e..61179caa7b2c8 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -654,6 +654,8 @@ static bool scsi_end_request(struct request *req, blk_status_t error,
>  	 */
>  	destroy_rcu_head(&cmd->rcu);
>  
> +	scsi_mpath_end_request(req);
> +
>  	/*
>  	 * In the MQ case the command gets freed by __blk_mq_end_request,
>  	 * so we have to do all cleanup that depends on it earlier.

This looks wrong. We start accounting in scsi_queue_rq(), and we need to
end it whenever we complete or requeue the request, otherwise the
accounting will get off. But not all requests go through
scsi_end_request(). scsi_mpath_failover_req(), for instance, calls
blk_mq_end_request() directly, and other functions, like
scsi_queue_insert() call blk_mq_requeue_request(). I'm pretty sure that
this should go in scsi_complete(), as well in the error path of
scsi_queue_rq().

-Ben