Re: [PATCH] ata: libata-eh: Clear scsicmd->result when setting SAM_STAT_CHECK_CONDITION

[Igor Pylypiv <ipylypiv@google.com>]

On Wed, Sep 04, 2024 at 10:37:27PM +0000, Igor Pylypiv wrote:
> commit 24aeebbf8ea9 ("scsi: ata: libata: Change ata_eh_request_sense() to
> not set CHECK_CONDITION") changed the way how SAM_STAT_CHECK_CONDITION is
> set. Assignment "scmd->result = SAM_STAT_CHECK_CONDITION;" was replaced by
> set_status_byte() which does not clear the scsicmd->result.
> 
> By not clearing the scsicmd->result we end up in a state where both
> the DID_TIME_OUT host byte and the SAM_STAT_CHECK_CONDITION status
> bytes are set.
> 
> The DID_TIME_OUT host byte is getting set a part of error handling:
> 
> ata_qc_complete()
>     ata_qc_schedule_eh()
>         blk_abort_request()
>             WRITE_ONCE(req->deadline, jiffies);
> 
> blk_mq_timeout_work()
>     blk_mq_check_expired()
>         blk_mq_rq_timed_out()
> 	    req->q->mq_ops->timeout() / scsi_timeout()
>                 set_host_byte(scmd, DID_TIME_OUT);
> 
> Having the host byte set to DID_TIME_OUT for a command that didn't timeout
> is confusing. Let's bring the old behavior back by setting scmd->result to
> SAM_STAT_CHECK_CONDITION.
> 
> Fixes: 24aeebbf8ea9 ("scsi: ata: libata: Change ata_eh_request_sense() to not set CHECK_CONDITION")
> Signed-off-by: Igor Pylypiv <ipylypiv@google.com>
> ---
>  drivers/ata/libata-eh.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
> index 214b935c2ced..4927b40e782f 100644
> --- a/drivers/ata/libata-eh.c
> +++ b/drivers/ata/libata-eh.c
> @@ -1605,7 +1605,7 @@ static unsigned int ata_eh_analyze_tf(struct ata_queued_cmd *qc)
>  		 */
>  		if (!(qc->flags & ATA_QCFLAG_SENSE_VALID) &&
>  		    (stat & ATA_SENSE) && ata_eh_request_sense(qc))
> -			set_status_byte(qc->scsicmd, SAM_STAT_CHECK_CONDITION);
> +			qc->scsicmd->result = SAM_STAT_CHECK_CONDITION;

Just realized that this needs a comment "/* Clear the host byte. */" to
prevent someone from changing it back to set_status_byte() in the future.
I'll add the comment in v2.

>  		if (err & ATA_ICRC)
>  			qc->err_mask |= AC_ERR_ATA_BUS;
>  		if (err & (ATA_UNC | ATA_AMNF))
> -- 
> 2.46.0.469.g59c65b2a67-goog
>