On Sat, May 13, 2023 at 06:12:27PM -0400, Tian Lan wrote:
> From: Tian Lan <tian.lan@xxxxxxxxxxxx>
>
> The nr_active counter continues to increase over time which causes the
> blk_mq_get_tag to hang until the thread is rescheduled to a different
> core despite there are still tags available.
>
> kernel-stack
>
> INFO: task inboundIOReacto:3014879 blocked for more than 2 seconds
> Not tainted 6.1.15-amd64 #1 Debian 6.1.15~debian11
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:inboundIOReacto state:D stack:0 pid:3014879 ppid:4557 flags:0x00000000
> Call Trace:
> <TASK>
> __schedule+0x351/0xa20
> scheduler+0x5d/0xe0
> io_schedule+0x42/0x70
> blk_mq_get_tag+0x11a/0x2a0
> ? dequeue_task_stop+0x70/0x70
> __blk_mq_alloc_requests+0x191/0x2e0
>
> kprobe output showing RQF_MQ_INFLIGHT bit is not cleared before
> __blk_mq_free_request being called.
>
> 320 320 kworker/29:1H __blk_mq_free_request rq_flags 0x220c0 in-flight 1
> b'__blk_mq_free_request+0x1 [kernel]'
> b'bt_iter+0x50 [kernel]'
> b'blk_mq_queue_tag_busy_iter+0x318 [kernel]'
> b'blk_mq_timeout_work+0x7c [kernel]'
> b'process_one_work+0x1c4 [kernel]'
> b'worker_thread+0x4d [kernel]'
> b'kthread+0xe6 [kernel]'
> b'ret_from_fork+0x1f [kernel]'
>
> Signed-off-by: Tian Lan <tian.lan@xxxxxxxxxxxx>
> ---
> block/blk-mq.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f6dad0886a2f..850bfb844ed2 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -683,6 +683,10 @@ static void __blk_mq_free_request(struct request *rq)
> blk_crypto_free_request(rq);
> blk_pm_mark_last_busy(rq);
> rq->mq_hctx = NULL;
> +
> + if (rq->rq_flags & RQF_MQ_INFLIGHT)
> + __blk_mq_dec_active_requests(hctx);
> +
> if (rq->tag != BLK_MQ_NO_TAG)
> blk_mq_put_tag(hctx->tags, ctx, rq->tag);
> if (sched_tag != BLK_MQ_NO_TAG)
> @@ -694,15 +698,11 @@ static void __blk_mq_free_request(struct request *rq)
> void blk_mq_free_request(struct request *rq)
> {
> struct request_queue *q = rq->q;
> - struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
>
> if ((rq->rq_flags & RQF_ELVPRIV) &&
> q->elevator->type->ops.finish_request)
> q->elevator->type->ops.finish_request(rq);
>
> - if (rq->rq_flags & RQF_MQ_INFLIGHT)
> - __blk_mq_dec_active_requests(hctx);
> -
> if (unlikely(laptop_mode && !blk_rq_is_passthrough(rq)))
> laptop_io_completion(q->disk->bdi);
This patch looks fine, but please add words about why this way fixes the issue
with fixes tag:
- the difference between blk_mq_free_request() and blk_mq_end_request_batch(),
wrt. when to call __blk_mq_dec_active_requests(), the former does it
before calling req_ref_put_and_test(), and the later decreases active
request after req_ref_put_and_test().
- Fixes: f794f3351f26 ("block: add support for blk_mq_end_request_batch()")
Once the above is done, feel free to add:
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Thanks,
Ming
