linux-kernel - Re: [PATCH v3 2/6] ata: libata-scsi: Do not overwrite valid sense data when CK

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Date: Fri, 28 Jun 2024 23:31:35 +0000
From: Igor Pylypiv <ipylypiv@...gle.com>
To: Niklas Cassel <cassel@...nel.org>
Cc: Damien Le Moal <dlemoal@...nel.org>, Tejun Heo <tj@...nel.org>,
	Hannes Reinecke <hare@...e.de>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v3 2/6] ata: libata-scsi: Do not overwrite valid sense
 data when CK_COND=1

On Fri, Jun 28, 2024 at 08:44:41PM +0200, Niklas Cassel wrote:
> On Thu, Jun 27, 2024 at 09:54:06PM +0000, Igor Pylypiv wrote:
> > 
> > Thank you, Niklas! I agree that this code is too complicated and should be
> > simplified. I don't think we should change the code too much in this patch
> > since it is going to be backported to stable releases.
> > 
> > Would you mind sending a patch for the proposed simplifications following
> > this patch series?
> > 
> 
> I would prefer if we changed it as part of this commit to be honest.
> 
> 
> I also re-read the SAT spec, and found that it says that:
> """
> If the CK_COND bit is set to:
> a) one, then the SATL shall return a status of CHECK CONDITION upon ATA command completion,
> without interpreting the contents of the STATUS field and returning the ATA fields from the request
> completion in the sense data as specified in table 209; and
> b) zero, then the SATL shall terminate the command with CHECK CONDITION status only if an error
> occurs in processing the command. See clause 11 for a description of ATA error conditions.
> """
> 
> So it seems quite clear that if CK_COND == 1, we should set CHECK CONDITION,
> so that answers the question/uncertainty I asked/expressed in earlier emails.
> 
> 
> I think this patch (which should be applied on top of your v3 series),
> makes the code way easier to read/understand:
> 

Agree, having self-explanatory variable names makes the code much more
readable. I'll add the patch in v4.

Do you mind if I set you as the author of the patch with the corresponding
Signed-off-by tag?

> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index d5874d4b9253..5b211551ac10 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -1659,26 +1656,27 @@ static void ata_scsi_qc_complete(struct ata_queued_cmd *qc)
>  {
>         struct scsi_cmnd *cmd = qc->scsicmd;
>         u8 *cdb = cmd->cmnd;
> -       int need_sense = (qc->err_mask != 0) &&
> -               !(qc->flags & ATA_QCFLAG_SENSE_VALID);
> -       int need_passthru_sense = (qc->err_mask != 0) ||
> -               (qc->flags & ATA_QCFLAG_SENSE_VALID);
> +       bool have_sense = qc->flags & ATA_QCFLAG_SENSE_VALID;
> +       bool is_ata_passthru = cdb[0] == ATA_16 || cdb[0] == ATA_12;
> +       bool is_ck_cond_request = cdb[2] & 0x20;
> +       bool is_error = qc->err_mask != 0;
>  
>         /* For ATA pass thru (SAT) commands, generate a sense block if
>          * user mandated it or if there's an error.  Note that if we
> -        * generate because the user forced us to [CK_COND =1], a check
> +        * generate because the user forced us to [CK_COND=1], a check
>          * condition is generated and the ATA register values are returned
>          * whether the command completed successfully or not. If there
> -        * was no error, we use the following sense data:
> +        * was no error, and CK_COND=1, we use the following sense data:
>          * sk = RECOVERED ERROR
>          * asc,ascq = ATA PASS-THROUGH INFORMATION AVAILABLE
>          */
> -       if (((cdb[0] == ATA_16) || (cdb[0] == ATA_12)) &&
> -           ((cdb[2] & 0x20) || need_passthru_sense)) {
> -               if (!(qc->flags & ATA_QCFLAG_SENSE_VALID))
> +       if (is_ata_passthru && (is_ck_cond_request || is_error || have_sense)) {
> +               if (!have_sense)
>                         ata_gen_passthru_sense(qc);
>                 ata_scsi_set_passthru_sense_fields(qc);
> -       } else if (need_sense) {
> +               if (is_ck_cond_request)
> +                       set_status_byte(qc->scsicmd, SAM_STAT_CHECK_CONDITION);

SAM_STAT_CHECK_CONDITION will be set by ata_gen_passthru_sense(). Perhaps we
can move the SAM_STAT_CHECK_CONDITION setting into else if?

        if (is_ata_passthru && (is_ck_cond_request || is_error || have_sense)) {
               if (!have_sense)
                       ata_gen_passthru_sense(qc);
               else if (is_ck_cond_request)
                       set_status_byte(qc->scsicmd, SAM_STAT_CHECK_CONDITION);
               ata_scsi_set_passthru_sense_fields(qc);
        } else if (is_error && !have_sense) {


> +       } else if (is_error && !have_sense) {
>                 ata_gen_ata_sense(qc);
>         } else {
>                 /* Keep the SCSI ML and status byte, clear host byte. */

Thanks,
Igor