Message-ID: <ZoMK-gpSbOWVFhf8@google.com>
Date: Mon, 1 Jul 2024 20:00:58 +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 Sat, Jun 29, 2024 at 05:09:54AM +0200, Niklas Cassel wrote:
> On Fri, Jun 28, 2024 at 11:31:35PM +0000, Igor Pylypiv wrote:
> > 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?
> 
> I still think that you are the author.
> 
> But if you want, feel free to add me as: Co-developed-by
> (which would also require you to add my Signed-off-by), see:
> https://www.kernel.org/doc/html/latest/process/submitting-patches.html#when-to-use-acked-by-cc-and-co-developed-by
> 
Sounds good! Added the Co-developed-by abd Signed-off-by tags in v4. Thanks!
> 
> > 
> > > 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?
> 
> I think it is fine that:
> if (is_ck_cond_request)
> 	set_status_byte(qc->scsicmd, SAM_STAT_CHECK_CONDITION);
> 
> might set SAM_STAT_CHECK_CONDITION even if it is already set.
> 
> Personally, I think that my suggestion is slightly clearer when it comes
> to highlight the behavior of CK_COND. (CK_COND will set CHECK_CONDITION,
> regardless if successful command or error command, and regardless if
> we already had sense or not.)
> 
> And considering that we finally make this hard to read code slightly more
> readable than it was to start off with, I would prefer my alternative.
>
It makes senes. Added the patch in v4. Thank you!
> 
> Kind regards,
> Niklas

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