linux-kernel - Re: [PATCH v2 6/6] ata: libata-scsi: Check ATA_QCFLAG_RTF_FILLED before using result

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Message-ID: <ZnthK-NjkSgIiGiE@google.com>
Date: Wed, 26 Jun 2024 00:30:35 +0000
From: Igor Pylypiv <ipylypiv@...gle.com>
To: Hannes Reinecke <hare@...e.de>
Cc: Damien Le Moal <dlemoal@...nel.org>, Niklas Cassel <cassel@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jason Yan <yanaijie@...wei.com>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/6] ata: libata-scsi: Check ATA_QCFLAG_RTF_FILLED
 before using result_tf

On Tue, Jun 25, 2024 at 08:26:59AM +0200, Hannes Reinecke wrote:
> On 6/25/24 00:12, Igor Pylypiv wrote:
> > qc->result_tf contents are only valid when the ATA_QCFLAG_RTF_FILLED flag
> > is set. The ATA_QCFLAG_RTF_FILLED flag should be always set for commands
> > that failed or for commands that have the ATA_QCFLAG_RESULT_TF flag set.
> > 
> > For ATA errors and ATA PASS-THROUGH commands the ATA_QCFLAG_RTF_FILLED
> > flag should be always set. Added WARN_ON_ONCE() checks to generate
> > a warning when ATA_QCFLAG_RTF_FILLED is not set and libata needs to
> > generate sense data.
> > 
> > Signed-off-by: Igor Pylypiv <ipylypiv@...gle.com>
> > ---
> >   drivers/ata/libata-scsi.c | 10 ++++++++++
> >   1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> > index e5669a296d81..7a8a08692ce9 100644
> > --- a/drivers/ata/libata-scsi.c
> > +++ b/drivers/ata/libata-scsi.c
> > @@ -246,6 +246,9 @@ static void ata_scsi_set_passthru_sense_fields(struct ata_queued_cmd *qc)
> >   	struct ata_taskfile *tf = &qc->result_tf;
> >   	unsigned char *sb = cmd->sense_buffer;
> >
> > +	if (WARN_ON_ONCE(!(qc->flags & ATA_QCFLAG_RTF_FILLED)))
> > +		return;
> > +
> >   	if ((sb[0] & 0x7f) >= 0x72) {
> >   		unsigned char *desc;
> >   		u8 len;
> > @@ -928,6 +931,9 @@ static void ata_gen_passthru_sense(struct ata_queued_cmd *qc)
> >   	unsigned char *sb = cmd->sense_buffer;
> >   	u8 sense_key, asc, ascq;
> > +	if (WARN_ON_ONCE(!(qc->flags & ATA_QCFLAG_RTF_FILLED)))
> > +		return;
> > +
> >   	/*
> >   	 * Use ata_to_sense_error() to map status register bits
> >   	 * onto sense key, asc & ascq.
> > @@ -971,6 +977,10 @@ static void ata_gen_ata_sense(struct ata_queued_cmd *qc)
> >   		ata_scsi_set_sense(dev, cmd, NOT_READY, 0x04, 0x21);
> >   		return;
> >   	}
> > +
> > +	if (WARN_ON_ONCE(!(qc->flags & ATA_QCFLAG_RTF_FILLED)))
> > +		return;
> > +
> >   	/* Use ata_to_sense_error() to map status register bits
> >   	 * onto sense key, asc & ascq.
> >   	 */
> 
> Hmm. Not sure if we really need the WARN_ON() here or whether a simple
> logging message wouldn't be sufficient; after all, we continue fine here.
> 

My worry about adding a simple log statement is that it might cause a log
spam if things go wrong for some reason.

This code is more like a "this should never happen" comment and we always
expect ATA_QCFLAG_RTF_FILLED to be present when generating sense data
based on ATA registers.

If WARN_ON_ONCE() is too much for this case I guess we can just remove it
and silently return?

Damien, Niklas, what are your thoughts on this?

Thanks,
Igor

> Cheers,
> 
> Hannes
> -- 
> Dr. Hannes Reinecke                  Kernel Storage Architect
> hare@...e.de                                +49 911 74053 688
> SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
> HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich
>