RE: +AFs-PATCH+AF0- blk-mq: Set request mapping to NULL in blk+AF8-mq+AF8-put+AF8-driver+AF8-tag

[Kashyap Desai <kashyap.desai@broadcom.com>]

> > > On Thu, Dec 06, 2018 at 11:15:13AM +0530, Kashyap Desai wrote:
> > > > >
> > > > > If the 'tag' passed to scsi_host_find_tag() is valid, I think
there
> > > > > shouldn't have such issue.
> > > > >
> > > > > If you want to find outstanding IOs, maybe you can try
> > > > > blk_mq_queue_tag_busy_iter()
> > > > > or blk_mq_tagset_busy_iter(), because you may not know if the
passed
> > > > 'tag'
> > > > > to
> > > > > scsi_host_find_tag() is valid or not.
> > > >
> > > > We tried quick change in mpt3sas driver using
blk_mq_tagset_busy_iter
> > and
> > > > it returns/callback for valid requests (no stale entries are
returned).
> > > > Expected.
> > > > Above two APIs are only for blk-mq.  What about non-mq case ?
Driver
> > > > should use scsi_host_find_tag for non-mq and
blk_mq_tagset_busy_iter
> > for
> > > > blk-mq case ?
> > >
> > > But your patch is only for blk-mq, is there same issue on non-mq
case?
> >
> > Problematic part from below function is code path which goes from "
> > shost_use_blk_mq(shost))".
> > Non-mq path works fine because every IO completion set bqt-
> >tag_index[tag]
> > = NULL from blk_queue_end_tag().
> >
> > I did similar things for mq path in this patch.
> >
> > static inline struct scsi_cmnd *scsi_host_find_tag(struct Scsi_Host
*shost,
> >                 int tag)
> > {
> >         struct request *req = NULL;
> >
> >         if (tag == SCSI_NO_TAG)
> >                 return NULL;
> >
> >         if (shost_use_blk_mq(shost)) {
> >                 u16 hwq = blk_mq_unique_tag_to_hwq(tag);
> >
> >                 if (hwq < shost->tag_set.nr_hw_queues) {
> >                         req =
blk_mq_tag_to_rq(shost->tag_set.tags[hwq],
> >                                 blk_mq_unique_tag_to_tag(tag));
> >                 }
> >         } else {
> >                 req = blk_map_queue_find_tag(shost->bqt, tag);
> >         }
>
>
> Hi Jens,
>
> Any conclusion/feedback on this topic/patch ?  As discussed, This is a
safe
> change and  good to have if no design issue.

Hi, Since we have not concluded on fix, we can resume discussion on next
revision of the patch. I will be posting V2 patch with complete fix.

Kashyap

>
> Kashyap