linux-kernel - Re: [PATCH v2] workqueue: Fix warning triggered when nr_running is checked in worker_enter

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Date:   Tue, 23 May 2023 09:40:16 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Zqiang <qiang.zhang1211@...il.com>
Cc:     jiangshanlai@...il.com, naresh.kamboju@...aro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] workqueue: Fix warning triggered when nr_running is
 checked in worker_enter_idle()

On Tue, May 23, 2023 at 10:09:41PM +0800, Zqiang wrote:
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 9c5c1cfa478f..329b84c42062 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1144,13 +1144,12 @@ void wq_worker_tick(struct task_struct *task)
>  	 * longer than wq_cpu_intensive_thresh_us, it's automatically marked
>  	 * CPU_INTENSIVE to avoid stalling other concurrency-managed work items.
>  	 */
> -	if ((worker->flags & WORKER_NOT_RUNNING) ||
> +	if ((worker->flags & WORKER_NOT_RUNNING) || worker->sleeping ||
>  	    worker->task->se.sum_exec_runtime - worker->current_at <
>  	    wq_cpu_intensive_thresh_us * NSEC_PER_USEC)
>  		return;

Ah, right, this isn't just interrupted read-modify-write. It has to consider
sleeping. This is subtle. We'll definitely need more comments. Will think
more about it.

Thanks.

-- 
tejun