Re: [PATCH v4 09/10] scsi: ufs: Introduce the function ufshcd_execute_start_stop()

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

On 10/18/22 3:29 PM, Bart Van Assche wrote:
> Open-code scsi_execute() because a later patch will modify scmd->flags
> and because scsi_execute() does not support setting scmd->flags. No
> functionality is changed.
> 
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  drivers/ufs/core/ufshcd.c | 39 ++++++++++++++++++++++++++++++++++-----
>  1 file changed, 34 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index 2a32bcc93d2e..c5ccc7ba583b 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -8729,6 +8729,39 @@ static void ufshcd_hba_exit(struct ufs_hba *hba)
>  	}
>  }
>  
> +static int ufshcd_execute_start_stop(struct scsi_device *sdev,
> +				     enum ufs_dev_pwr_mode pwr_mode,
> +				     struct scsi_sense_hdr *sshdr)
> +{
> +	unsigned char cdb[6] = { START_STOP, 0, 0, 0, pwr_mode << 4, 0 };
> +	struct request *req;
> +	struct scsi_cmnd *scmd;
> +	int ret;
> +
> +	req = scsi_alloc_request(sdev->request_queue, REQ_OP_DRV_IN,
> +				 BLK_MQ_REQ_PM);
>

Can you hit a case where we have run out of tags (__blk_mq_alloc_requests
is hitting the blk_mq_get_tag == BLK_MQ_NO_TAG check), the host has gone
into recovery and so commands are completing to add a tag back and then we
try to call this and get stuck waiting on a tag? Or for passthrough do we
have some special reserve?

If so do you need to use BLK_MQ_REQ_NOWAIT here? Maybe do the retry loop
yourself like:

retry:
	if host is in recovery
		return failure

	req = scsi_alloc_request(.... BLK_MQ_REQ_NOWAIT)
	if (!req and we have not hit some retry limit)
		goto retry


or have some special reserve command/tag.