Re: [PATCH RFC v3 1/7] ata: libata-scsi: Add ata_scsi_queue_internal()

[John Garry]

On 27/10/2022 02:42, Damien Le Moal wrote:
> On 10/25/22 19:32, John Garry wrote:
> > Add a function to handle queued ATA internal SCSI cmnds - does much the
> > same as ata_exec_internal_sg() does (which will be fixed up later to
> > actually queue internal cmnds through this function).
> >
> > Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
> > ---
> >   drivers/ata/libata-sata.c |  3 +++
> >   drivers/ata/libata-scsi.c | 43 +++++++++++++++++++++++++++++++++++++++
> >   drivers/ata/libata.h      |  3 ++-
> >   include/linux/libata.h    |  6 ++++++
> >   4 files changed, 54 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
> > index b6806d41a8c5..e8b828c56542 100644
> > --- a/drivers/ata/libata-sata.c
> > +++ b/drivers/ata/libata-sata.c
> > @@ -1258,6 +1258,9 @@ int ata_sas_queuecmd(struct scsi_cmnd *cmd, struct ata_port *ap)
> >   {
> >   	int rc = 0;
> >   
> > +	if (blk_mq_is_reserved_rq(scsi_cmd_to_rq(cmd)))
> > +		return ata_scsi_queue_internal(cmd, ap->link.device);
> > +
> >   	if (likely(ata_dev_enabled(ap->link.device)))
> >   		rc = __ata_scsi_queuecmd(cmd, ap->link.device);
> >   	else {
> > diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> > index 476e0ef4bd29..30d7c90b0c35 100644
> > --- a/drivers/ata/libata-scsi.c
> > +++ b/drivers/ata/libata-scsi.c
> > @@ -3965,6 +3965,49 @@ static inline ata_xlat_func_t ata_get_xlat_func(struct ata_device *dev, u8 cmd)
> >   	return NULL;
> >   }
> >   
> > +unsigned int ata_scsi_queue_internal(struct scsi_cmnd *scmd,
> > +				     struct ata_device *dev)
> > +{
> > +	struct ata_link *link = dev->link;
> > +	struct ata_port *ap = link->ap;
> > +	struct ata_queued_cmd *qc;
> > +
> > +	/* no internal command while frozen */
> > +	if (ap->pflags & ATA_PFLAG_FROZEN)
> > +		goto did_err;
> > +
> > +	/* initialize internal qc */
> > +	qc = __ata_qc_from_tag(ap, ATA_TAG_INTERNAL);
> > +	link->preempted_tag = link->active_tag;
> > +	link->preempted_sactive = link->sactive;
> > +	ap->preempted_qc_active = ap->qc_active;
> > +	ap->preempted_nr_active_links = ap->nr_active_links;
> > +	link->active_tag = ATA_TAG_POISON;
> > +	link->sactive = 0;
> > +	ap->qc_active = 0;
> > +	ap->nr_active_links = 0;
> > +
> > +	if (qc->dma_dir != DMA_NONE) {
> > +		int n_elem;
> > +
> > +		n_elem = 1;
> > +		qc->n_elem = n_elem;
> > +		qc->sg = scsi_sglist(scmd);
> > +		qc->nbytes = qc->sg->length;
> > +		ata_sg_init(qc, qc->sg, n_elem);
> > +	}
> > +
> > +	scmd->submitter = SUBMITTED_BY_BLOCK_LAYER;
> > +
> > +	ata_qc_issue(qc);
>
> Arg, no ! This potentially mixes NCQ and non-NCQ commands, which is
> forbidden by ATA spec. You need to use something like:
>
> 	if (ap->ops->qc_defer) {
> 		if ((rc = ap->ops->qc_defer(qc)))
> 			goto defer;
> 	}
>
> 	ata_qc_issue(qc);
>
> which is done in __ata_scsi_queuecmd() -> ata_scsi_translate()
>
> Unless you guarantee that ata_scsi_queue_internal() is always called
> from libata EH context ?

This will be called synchronously called from ata_exec_internal_sg(), so 
the same rules on NCQ vs non-NCQ would apply here. As I see, 
ata_exec_internal_sg() assumes non-NCQ mode and is not multi-thread safe.

Thanks,
John

> > +
> > +	return 0;
> > +did_err:
> > +	scmd->result = (DID_ERROR << 16);
> > +	scsi_done(scmd);
> > +	return 0;
> > +}
> > +
> >   int __ata_scsi_queuecmd(struct scsi_cmnd *scmd, struct ata_device *dev)
> >   {
> >   	u8 scsi_op = scmd->cmnd[0];
> > diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
> > index 0c2df1e60768..15cd1cd618b8 100644
> > --- a/drivers/ata/libata.h
> > +++ b/drivers/ata/libata.h
> > @@ -82,7 +82,6 @@ extern int ata_port_probe(struct ata_port *ap);
> >   extern void __ata_port_probe(struct ata_port *ap);
> >   extern unsigned int ata_read_log_page(struct ata_device *dev, u8 log,
> >   				      u8 page, void *buf, unsigned int sectors);
> > -
> >   #define to_ata_port(d) container_of(d, struct ata_port, tdev)
> >   
> >   /* libata-acpi.c */
> > @@ -130,6 +129,8 @@ extern int ata_scsi_user_scan(struct Scsi_Host *shost, unsigned int channel,
> >   void ata_scsi_sdev_config(struct scsi_device *sdev);
> >   int ata_scsi_dev_config(struct scsi_device *sdev, struct ata_device *dev);
> >   int __ata_scsi_queuecmd(struct scsi_cmnd *scmd, struct ata_device *dev);
> > +unsigned int ata_scsi_queue_internal(struct scsi_cmnd *scmd,
> > +				     struct ata_device *dev);
> >   
> >   /* libata-eh.c */
> >   extern unsigned int ata_internal_cmd_timeout(struct ata_device *dev, u8 cmd);
> > diff --git a/include/linux/libata.h b/include/linux/libata.h
> > index 827d5838cd23..8938b584520f 100644
> > --- a/include/linux/libata.h
> > +++ b/include/linux/libata.h
> > @@ -764,7 +764,9 @@ struct ata_link {
> >   
> >   	struct device		tdev;
> >   	unsigned int		active_tag;	/* active tag on this link */
> > +	unsigned int		preempted_tag;
> >   	u32			sactive;	/* active NCQ commands */
> > +	u32			preempted_sactive;
> >   
> >   	unsigned int		flags;		/* ATA_LFLAG_xxx */
> >   
> > @@ -857,6 +859,10 @@ struct ata_port {
> >   #ifdef CONFIG_ATA_ACPI
> >   	struct ata_acpi_gtm	__acpi_init_gtm; /* use ata_acpi_init_gtm() */
> >   #endif
> > +
> > +	u64 preempted_qc_active;
> > +	int preempted_nr_active_links;
> > +
> >   	/* owned by EH */
> >   	u8			sector_buf[ATA_SECT_SIZE] ____cacheline_aligned;
> >   };