[PATCH V2 0/3] blk-mq: misc fixes

[PATCH V2 0/3] blk-mq: misc fixes

[Ming Lei]

Hello,

Here are 3 small fixes against latest linus tree.

V2:
	- move batched update into blk_mq_flush_tag_batch() as suggested by
	  Jens, 3/3

Ming Lei (3):
  blk-mq: only try to run plug merge if request has same queue with
    incoming bio
  blk-mq: add RQF_ELV debug entry
  blk-mq: update hctx->nr_active in blk_mq_end_request_batch()

 block/blk-merge.c      |  6 ++++--
 block/blk-mq-debugfs.c |  1 +
 block/blk-mq.c         |  7 +++++++
 block/blk-mq.h         | 12 +++++++++---
 4 files changed, 21 insertions(+), 5 deletions(-)

-- 
2.31.1

[PATCH V2 1/3] blk-mq: only try to run plug merge if request has same queue with incoming bio

[Ming Lei]

It is obvious that io merge can't be done between two different queues, so
just try to run io merge in case of same queue.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-merge.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index df69f4bb7717..893c1a60b701 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -1101,9 +1101,11 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 		 * the same queue, there should be only one such rq in a queue
 		 */
 		*same_queue_rq = true;
+
+		if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
+				BIO_MERGE_OK)
+			return true;
 	}
-	if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) == BIO_MERGE_OK)
-		return true;
 	return false;
 }
 
-- 
2.31.1

[PATCH V2 2/3] blk-mq: add RQF_ELV debug entry

[Ming Lei]

Looks it is missed so add it.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-debugfs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index f5076c173477..4f2cf8399f3d 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -308,6 +308,7 @@ static const char *const rqf_name[] = {
 	RQF_NAME(SPECIAL_PAYLOAD),
 	RQF_NAME(ZONE_WRITE_LOCKED),
 	RQF_NAME(MQ_POLL_SLEPT),
+	RQF_NAME(ELV),
 };
 #undef RQF_NAME
 
-- 
2.31.1

[PATCH V2 3/3] blk-mq: update hctx->nr_active in blk_mq_end_request_batch()

[Ming Lei]

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@wdc.com>
Fixes: f794f3351f26 ("block: add support for blk_mq_end_request_batch()")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c |  7 +++++++
 block/blk-mq.h | 12 +++++++++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 07eb1412760b..2a2c57c98bbd 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -815,6 +815,13 @@ static inline void blk_mq_flush_tag_batch(struct blk_mq_hw_ctx *hctx,
 {
 	struct request_queue *q = hctx->queue;
 
+	/*
+	 * All requests should have been marked as RQF_MQ_INFLIGHT, so
+	 * update hctx->nr_active in batch
+	 */
+	if (hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)
+		__blk_mq_sub_active_requests(hctx, nr_tags);
+
 	blk_mq_put_tags(hctx->tags, tag_array, 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)
-- 
2.31.1

Re: [PATCH V2 3/3] blk-mq: update hctx->nr_active in blk_mq_end_request_batch()

[Shinichiro Kawasaki]

On Nov 02, 2021 / 23:36, 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@wdc.com>
> Fixes: f794f3351f26 ("block: add support for blk_mq_end_request_batch()")
> Signed-off-by: Ming Lei <ming.lei@redhat.com>

Ming, thank you very much. I have confirmed that the blktests block/005 hang
disappears using NVMe devices with two namespaces.

Though this patch is already queued up to for-5.16/block, in case it is still
meaningful:

Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>

-- 
Best Regards,
Shin'ichiro Kawasaki

Re: [PATCH V2 3/3] blk-mq: update hctx->nr_active in blk_mq_end_request_batch()

[Jens Axboe]

On 11/2/21 4:43 PM, Shinichiro Kawasaki wrote:
> On Nov 02, 2021 / 23:36, 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@wdc.com>
>> Fixes: f794f3351f26 ("block: add support for blk_mq_end_request_batch()")
>> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> 
> Ming, thank you very much. I have confirmed that the blktests block/005 hang
> disappears using NVMe devices with two namespaces.
> 
> Though this patch is already queued up to for-5.16/block, in case it is still
> meaningful:
> 
> Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>

Testing is _always_ meaningful! So thanks for doing that, and reporting it in
the first place. The patch has been queued up this morning for 5.16.

-- 
Jens Axboe

Re: [PATCH V2 0/3] blk-mq: misc fixes

[Jens Axboe]

On 11/2/21 9:36 AM, Ming Lei wrote:
> Hello,
> 
> Here are 3 small fixes against latest linus tree.
> 
> V2:
> 	- move batched update into blk_mq_flush_tag_batch() as suggested by
> 	  Jens, 3/3

Thanks Ming, applied.

-- 
Jens Axboe