On 11/2/21 9:20 AM, Jens Axboe wrote:
> 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.
Something like this, untested. FWIW, I did apply 1-2 from this series,
so just do a v2 of 3/3 and that should do it.
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 02f70dc06ced..18dee9af4487 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -817,6 +817,8 @@ static inline void blk_mq_flush_tag_batch(struct blk_mq_hw_ctx *hctx,
struct request_queue *q = hctx->queue;
blk_mq_put_tags(hctx->tags, tag_array, nr_tags);
+ if (hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)
+ __blk_mq_sub_active_requests(hctx, nr_tags);
percpu_ref_put_many(&q->q_usage_counter, nr_tags);
}
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 28859fc5faee..cb0b5482ca5e 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -225,12 +225,18 @@ static inline void __blk_mq_inc_active_requests(struct blk_mq_hw_ctx *hctx)
atomic_inc(&hctx->nr_active);
}
-static inline void __blk_mq_dec_active_requests(struct blk_mq_hw_ctx *hctx)
+static inline void __blk_mq_sub_active_requests(struct blk_mq_hw_ctx *hctx,
+ int val)
{
if (blk_mq_is_shared_tags(hctx->flags))
- atomic_dec(&hctx->queue->nr_active_requests_shared_tags);
+ atomic_sub(val, &hctx->queue->nr_active_requests_shared_tags);
else
- atomic_dec(&hctx->nr_active);
+ atomic_sub(val, &hctx->nr_active);
+}
+
+static inline void __blk_mq_dec_active_requests(struct blk_mq_hw_ctx *hctx)
+{
+ __blk_mq_sub_active_requests(hctx, 1);
}
static inline int __blk_mq_active_requests(struct blk_mq_hw_ctx *hctx)
--
Jens Axboe
