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Date: Thu, 25 May 2023 10:12:26 +0800
From: Ming Lei <ming.lei@redhat.com>
To: Tian Lan <tilan7663@gmail.com>
Cc: hare@suse.de, axboe@kernel.dk, horms@kernel.org,
	linux-block@vger.kernel.org, lkp@intel.com, llvm@lists.linux.dev,
	oe-kbuild-all@lists.linux.dev, tian.lan@twosigma.com
Subject: Re: [PATCH] blk-mq: fix blk_mq_hw_ctx active request accounting
Message-ID: <ZG7ECteMoJah+UqU@ovpn-8-21.pek2.redhat.com>
References: <1c9fc9df-817c-e6cb-1375-2013c0c5a9bb@suse.de>
 <20230515122643.597546-1-tilan7663@gmail.com>
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X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9

On Mon, May 15, 2023 at 08:26:43AM -0400, Tian Lan wrote:
> From: Tian Lan <tian.lan@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:inboundIORe 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
>          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]'
> 
> The issue is caused by 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 latter
> decreases the active request after req_ref_put_and_test().
> 
> - Fixes: f794f3351f26 ("block: add support for blk_mq_end_request_batch()")
> 
> Signed-off-by: Tian Lan <tian.lan@twosigma.com>
> Reviewed-by: Ming Lei <ming.lei@redhat.com>
> Reviewed-by: Hannes Reinecke <hare@suse.de>

Hello Jens,

Looks this fix is missed, can you take a look?


Thanks,
Ming