Re: [PATCH 1/2] libata: Fix scsi_host can_queue issue in ata_qc_new()

[Mike Qiu]

On 07/22/2014 11:42 PM, Tejun Heo wrote:
> Hello,
>
> (cc'ing Dan)
>
> On Tue, Jul 22, 2014 at 10:50:19AM -0400, Mike Qiu wrote:
> > The can_queue in scsi_host can be more than ATA_MAX_QUEUE (32),
> > for example, in ipr, it can be 100 or more.
> >
> > Also, some drivers, like ipr driver, haven't filled the field
> > scsi_host in ata_port, and will lead a call trace, so add
> > check for that.
> >
> > Signed-off-by: Mike Qiu <qiudayu@xxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/ata/libata-core.c | 15 ++++-----------
> >   1 file changed, 4 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> > index 259d879..a5b9c70 100644
> > --- a/drivers/ata/libata-core.c
> > +++ b/drivers/ata/libata-core.c
> > @@ -4734,7 +4734,10 @@ static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
> >   	struct ata_queued_cmd *qc = NULL;
> >   	unsigned int i, tag, max_queue;
> >   
> > -	max_queue = ap->scsi_host->can_queue;
> > +	if (ap->scsi_host && ap->scsi_host->can_queue <= ATA_MAX_QUEUE)
> > +		max_queue = ap->scsi_host->can_queue;
> > +	else
> > +		max_queue = ATA_MAX_QUEUE;
> >   
> >   	/* no command while frozen */
> >   	if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
> > @@ -6109,16 +6112,6 @@ int ata_host_register(struct ata_host *host, struct scsi_host_template *sht)
> >   {
> >   	int i, rc;
> >   
> > -	/*
> > -	 * The max queue supported by hardware must not be greater than
> > -	 * ATA_MAX_QUEUE.
> > -	 */
> > -	if (sht->can_queue > ATA_MAX_QUEUE) {
> > -		dev_err(host->dev, "BUG: the hardware max queue is too large\n");
> > -		WARN_ON(1);
> > -		return -EINVAL;
> > -	}
> > -
> So, ummm, I really don't like that we're adding the conditionals to
> the hot path (yeah, its implementation is slow but still).  Maybe we

Yes, agree ..., not a good idea to do this...

Thanks
Mike
> need to store the chosen queue depth after all?  Dan?
>
> Thanks.

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