On Tue, Nov 02, 2021 at 07:47:44AM -0600, Jens Axboe wrote:
> On 11/2/21 7:35 AM, Ming Lei wrote:
> > In case of shared tags and none io sched, batched completion still may
> > be run into, and hctx->nr_active is accounted when getting driver tag,
> > so it has to be updated in blk_mq_end_request_batch().
> >
> > Otherwise, hctx->nr_active may become same with queue depth, then
> > hctx_may_queue() always return false, then io hang is caused.
> >
> > Fixes the issue by updating the counter in batched way.
> >
> > Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
> > Fixes: f794f3351f26 ("block: add support for blk_mq_end_request_batch()")
> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > ---
> > block/blk-mq.c | 15 +++++++++++++--
> > block/blk-mq.h | 12 +++++++++---
> > 2 files changed, 22 insertions(+), 5 deletions(-)
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 07eb1412760b..0dbe75034f61 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -825,6 +825,7 @@ void blk_mq_end_request_batch(struct io_comp_batch *iob)
> > struct blk_mq_hw_ctx *cur_hctx = NULL;
> > struct request *rq;
> > u64 now = 0;
> > + int active = 0;
> >
> > if (iob->need_ts)
> > now = ktime_get_ns();
> > @@ -846,16 +847,26 @@ void blk_mq_end_request_batch(struct io_comp_batch *iob)
> > rq_qos_done(rq->q, rq);
> >
> > if (nr_tags == TAG_COMP_BATCH || cur_hctx != rq->mq_hctx) {
> > - if (cur_hctx)
> > + if (cur_hctx) {
> > + if (active)
> > + __blk_mq_sub_active_requests(cur_hctx,
> > + active);
> > blk_mq_flush_tag_batch(cur_hctx, tags, nr_tags);
> > + }
> > nr_tags = 0;
> > + active = 0;
> > cur_hctx = rq->mq_hctx;
> > }
> > tags[nr_tags++] = rq->tag;
> > + if (rq->rq_flags & RQF_MQ_INFLIGHT)
> > + active++;
>
> Are there any cases where either none or all of requests have the flag set, and
> hence active == nr_tags?
none and BLK_MQ_F_TAG_QUEUE_SHARED, and Shinichiro only observed the
issue on two NSs.
Thanks,
Ming
