linux-kernel - Re: [PATCH v2] blk-mq: release scheduler resource when request complete

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Date:   Thu, 17 Aug 2023 07:50:38 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     chengming.zhou@...ux.dev
Cc:     oe-lkp@...ts.linux.dev, lkp@...el.com,
        Chuck Lever <chuck.lever@...cle.com>,
        linux-block@...r.kernel.org, axboe@...nel.dk, hch@....de,
        cel@...nel.org, linux-kernel@...r.kernel.org,
        zhouchengming@...edance.com,
        kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH v2] blk-mq: release scheduler resource when request
 complete

On 8/17/23 07:41, kernel test robot wrote:
> [  222.622837][ T2216] statistics for priority 1: i 276 m 0 d 276 c 278
> [ 222.629307][ T2216] WARNING: CPU: 0 PID: 2216 at block/mq-deadline.c:680 dd_exit_sched (block/mq-deadline.c:680 (discriminator 3))

The above information shows that dd_inserted_request() has been called
276 times and also that dd_finish_request() has been called 278 times.
Calling dd_finish_request() more than once per request breaks the code
for priority handling since that code checks how many requests are
pending per priority level by subtracting the number of completion calls
from the number of insertion calls (see also dd_queued()). I think the
above output indicates that this patch introduced a regression.

Bart.