Re: [PATCH 1/1] scsi_dh_alua: properly handling the ALUA transitioning state

[Hannes Reinecke <hare@suse.de>]

On 5/2/22 08:09, Brian Bunker wrote:
> The handling of the ALUA transitioning state is currently broken. When
> a target goes into this state, it is expected that the target is
> allowed to stay in this state for the implicit transition timeout
> without a path failure. The handler has this logic, but it gets
> skipped currently.
> 
> When the target transitions, there is in-flight I/O from the
> initiator. The first of these responses from the target will be a unit
> attention letting the initiator know that the ALUA state has changed.
> The remaining in-flight I/Os, before the initiator finds out that the
> portal state has changed, will return not ready, ALUA state is
> transitioning. The portal state will change to
> SCSI_ACCESS_STATE_TRANSITIONING. This will lead to all new I/O
> immediately failing the path unexpectedly. The path failure happens in
> less than a second instead of the expected successes until the
> transition timer is exceeded.
> 
> This change allows I/Os to continue while the path is in the ALUA
> transitioning state. The handler already takes care of a target that
> stays in the transitioning state for too long by changing the state to
> ALUA state standby once the transition timeout is exceeded at which
> point the path will fail.
> 
> Signed-off-by: Brian Bunker <brian@purestorage.com>
> Acked-by: Krishna Kant <krishna.kant@purestorage.com>
> Acked-by: Seamus Connor <sconnor@purestorage.com>
> ___
> diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c
> b/drivers/scsi/device_handler/scsi_dh_alua.c
> index 37d06f993b76..1d9be771f3ee 100644
> --- a/drivers/scsi/device_handler/scsi_dh_alua.c
> +++ b/drivers/scsi/device_handler/scsi_dh_alua.c
> @@ -1172,9 +1172,8 @@ static blk_status_t alua_prep_fn(struct
> scsi_device *sdev, struct request *req)
>          case SCSI_ACCESS_STATE_OPTIMAL:
>          case SCSI_ACCESS_STATE_ACTIVE:
>          case SCSI_ACCESS_STATE_LBA:
> -               return BLK_STS_OK;
>          case SCSI_ACCESS_STATE_TRANSITIONING:
> -               return BLK_STS_AGAIN;
> +               return BLK_STS_OK;
>          default:
>                  req->rq_flags |= RQF_QUIET;
>                  return BLK_STS_IOERR;

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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