linux-kernel - 回复: [PATCH] io-wq: set task TASK_INTERRUPTIBLE state before schedule

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Message-ID: <BYAPR11MB2632A45DB4DA30E34D412528FF170@BYAPR11MB2632.namprd11.prod.outlook.com>
Date:   Wed, 28 Oct 2020 02:47:53 +0000
From:   "Zhang, Qiang" <Qiang.Zhang@...driver.com>
To:     Jens Axboe <axboe@...nel.dk>
CC:     "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: 回复: [PATCH] io-wq: set task TASK_INTERRUPTIBLE state before schedule_timeout



________________________________________
发件人: Jens Axboe <axboe@...nel.dk>
发送时间: 2020年10月27日 21:35
收件人: Zhang, Qiang
抄送: io-uring@...r.kernel.org; linux-kernel@...r.kernel.org
主题: Re: [PATCH] io-wq: set task TASK_INTERRUPTIBLE state before schedule_timeout

On 10/26/20 9:09 PM, qiang.zhang@...driver.com wrote:
> From: Zqiang <qiang.zhang@...driver.com>
>
> In 'io_wqe_worker' thread, if the work which in 'wqe->work_list' be
> finished, the 'wqe->work_list' is empty, and after that the
> '__io_worker_idle' func return false, the task state is TASK_RUNNING,
> need to be set TASK_INTERRUPTIBLE before call schedule_timeout func.
>
>I don't think that's safe - what if someone added work right before you
>call schedule_timeout_interruptible? Something ala:
>
>
>io_wq_enqueue()
>                        set_current_state(TASK_INTERRUPTIBLE();
>                        schedule_timeout(WORKER_IDLE_TIMEOUT);
>
>then we'll have work added and the task state set to running, but the
>worker itself just sets us to non-running and will hence wait
>WORKER_IDLE_TIMEOUT before the work is processed.
>
>The current situation will do one extra loop for this case, as the
>schedule_timeout() just ends up being a nop and we go around again

although the worker task state is running,  due to the call schedule_timeout, the 
current worker still possible to be switched out.
if set current worker task is no-running, the current worker be switched out, but
the schedule will call io_wq_worker_sleeping func  to wake up free worker task, if 
wqe->free_list is not empty.  

>checking for work. Since we already unused the mm, the next iteration
>will go to sleep properly unless new work came in.
>
>--
>Jens Axboe