Subject: Re: next: WARNING: CPU: 0 PID: 63 at kernel/workqueue.c:1999 worker_enter_idle+0xb2/0xc0

From: Tejun Heo <[email-masked]>
Date: Mon, 22 May 2023 08:20:38 -1000

Hello,

On Mon, May 22, 2023 at 09:24:09PM +0800, Z qiang wrote:
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 9c5c1cfa478f..f8d739fef311 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1060,10 +1060,9 @@ void wq_worker_running(struct task_struct *task)
>          * and leave with an unexpected pool->nr_running == 1 on the newly
> unbound
>          * pool. Protect against such race.
>          */
> -       preempt_disable();
> +       local_irq_disable();
>         if (!(worker->flags & WORKER_NOT_RUNNING))
>                 worker->pool->nr_running++;
> -       preempt_enable();
> 
>         /*
>          * CPU intensive auto-detection cares about how long a work item
> hogged
> @@ -1072,6 +1071,7 @@ void wq_worker_running(struct task_struct *task)
>         worker->current_at = worker->task->se.sum_exec_runtime;
> 
>         worker->sleeping = 0;
> +       local_irq_enable();
>  }

Ah, yeah, this is correct. Now we're modifying nr_running from timer tick
too, so if don't block irq, the timer tick can ruin the not-irq-protected
read-write-modify nr_running update from wq_worker_running(). Naresh, can
you please confirm the fix?

Thanks.

-- 
tejun