On 11/2/21 9:08 AM, Ming Lei wrote: > On Tue, Nov 02, 2021 at 08:57:41AM -0600, Jens Axboe wrote: >> On 11/2/21 7:57 AM, Ming Lei wrote: >>> 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. >> >> Maybe I wasn't clear enough. What I'm saying is that either all of the >> requests will have RQF_MQ_INFLIGHT set, or none of them. Hence active >> should be either 0, or == nr_tags. > > Yeah, that is right since BLK_MQ_F_TAG_QUEUE_SHARED is updated after > queue is frozen. Meantime blk_mq_end_request_batch() is only called > for ending successfully completed requests. > > Will do that in V2. Thanks, then it just becomes a single check in blk_mq_flush_tag_batch(), which is a lot better than per-request. -- Jens Axboe