>
> 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 ?
I don't see that will be good interface. Also, blk_mq_tagset_busy_iter API
does not provide control if driver wants to quit in-between or do some
retry logic etc.
Why can't we add single API which provides the correct output.
scsi_host_find_tag () API works well in non-mq case because,
blk_queue_end_tag() set bqt->tag_index[tag] = NULL;.
We are missing similar reset upon request completion in blk-mq case. This
patch has similar approach as non-mq and there is no race condition I can
foresee.
BTW - My original patch is half fix. We also need below changes -
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3f91c6e..d8f53ac 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -477,8 +477,10 @@ static void __blk_mq_free_request(struct request *rq)
const int sched_tag = rq->internal_tag;
blk_pm_mark_last_busy(rq);
- if (rq->tag != -1)
+ if (rq->tag != -1) {
+ hctx->tags->rqs[rq->tag] = NULL;
blk_mq_put_tag(hctx, hctx->tags, ctx, rq->tag);
+ }
if (sched_tag != -1)
blk_mq_put_tag(hctx, hctx->sched_tags, ctx, sched_tag);
blk_mq_sched_restart(hctx);
>
>
> Thanks,
> Ming
