ACK/CMT: [SRU][j:linux-gke][PATCH 1/1] blk-mq: fix blk_mq_hw_ctx active request accounting
Jian Hui Lee
jianhui.lee at canonical.com
Mon Nov 4 02:41:41 UTC 2024
Hi Ian,
Missing the bug link in the patch description. Please add it while
committing the change.
Other than that,
Acked-by: Jian Hui Lee <jianhui.lee at canonical.com>
On Wed, Oct 30, 2024 at 11:51 PM Ian Whitfield
<ian.whitfield at canonical.com> wrote:
>
> From: Tian Lan <tian.lan at twosigma.com>
>
> 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 at twosigma.com>
> Fixes: 2e315dc07df0 ("blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter")
> Reviewed-by: Ming Lei <ming.lei at redhat.com>
> Link: https://lore.kernel.org/r/20230513221227.497327-1-tilan7663@gmail.com
> Signed-off-by: Jens Axboe <axboe at kernel.dk>
> (backported from commit ddad59331a4e16088468ca0ad228a9fe32d7955a)
> [ijwhitfield: Context adjusted due to missing commits:
> 9a14d6ce4135 ("block: remove debugfs blk_mq_ctx dispatched/merged/completed attributes")
> 222ee581b845 ("block: move the remaining elv.icq handling to the I/O scheduler")]
> Signed-off-by: Ian Whitfield <ian.whitfield at canonical.com>
> ---
> 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 d80ebba16778..79030318e821 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -506,6 +506,10 @@ 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)
> @@ -519,7 +523,6 @@ void blk_mq_free_request(struct request *rq)
> struct request_queue *q = rq->q;
> struct elevator_queue *e = q->elevator;
> struct blk_mq_ctx *ctx = rq->mq_ctx;
> - struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
>
> if (rq->rq_flags & RQF_ELVPRIV) {
> if (e && e->type->ops.finish_request)
> @@ -531,9 +534,6 @@ void blk_mq_free_request(struct request *rq)
> }
>
> ctx->rq_completed[rq_is_sync(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);
>
> --
> 2.43.0
>
>
> --
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