Re: [PATCH v4 03/10] scsi: core: Support failing requests while recovering

[Mike Christie <michael.christie@oracle.com>]

On 10/18/22 3:29 PM, Bart Van Assche wrote:
> The current behavior for SCSI commands submitted while error recovery
> is ongoing is to retry command submission after error recovery has
> finished. See also the scsi_host_in_recovery() check in
> scsi_host_queue_ready(). Add support for failing SCSI commands while
> host recovery is in progress. This functionality will be used to fix a
> deadlock in the UFS driver.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: John Garry <john.garry@huawei.com>
> Cc: Mike Christie <michael.christie@oracle.com>
> Cc: Hannes Reinecke <hare@suse.de>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  drivers/scsi/scsi_lib.c  | 8 +++++---
>  include/scsi/scsi_cmnd.h | 3 ++-
>  2 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index fa96d3cfdfa3..ec890865abae 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1341,9 +1341,6 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
>  				   struct scsi_device *sdev,
>  				   struct scsi_cmnd *cmd)
>  {
> -	if (scsi_host_in_recovery(shost))
> -		return 0;
> -
>  	if (atomic_read(&shost->host_blocked) > 0) {
>  		if (scsi_host_busy(shost) > 0)
>  			goto starved;
> @@ -1732,6 +1729,11 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
>  	ret = BLK_STS_RESOURCE;
>  	if (!scsi_target_queue_ready(shost, sdev))
>  		goto out_put_budget;
> +	if (unlikely(scsi_host_in_recovery(shost))) {
> +		if (cmd->flags & SCMD_FAIL_IF_RECOVERING)
> +			ret = BLK_STS_OFFLINE;
> +		goto out_dec_target_busy;
> +	}

Hey,

Will we always hit this check? For example, if we have hit the
device's queue depth limit so

scsi_mq_get_budget -> scsi_dev_queue_ready

is returning -1, will we not even call scsi_queue_rq? So because
we are in recovery and no commands are completing, we will be
stuck waiting for a token to be put back on the sdev->budget_map.

Do you need a similar check in scsi_dev_queue_ready or should
the check go in there only or can we hit a race for the latter?