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

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On Thu, Dec 06, 2018 at 11:15:13AM +0530, Kashyap Desai wrote:

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If the 'tag' passed to scsi_host_find_tag() is valid, I think

there

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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

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'tag'

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to
scsi_host_find_tag() is valid or not.

We tried quick change in mpt3sas driver using

blk_mq_tagset_busy_iter

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and

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it returns/callback for valid requests (no stale entries are

returned).

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Expected.
Above two APIs are only for blk-mq.  What about non-mq case ?

Driver

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should use scsi_host_find_tag for non-mq and

blk_mq_tagset_busy_iter

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for

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blk-mq case ?

But your patch is only for blk-mq, is there same issue on non-mq

case?

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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,

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                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],

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                                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