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 11:12:07 -1000

On Mon, May 22, 2023 at 08:20:38AM -1000, Tejun Heo wrote:
> 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?

Z qiang, while waiting for Naresh's test result, can you send the fix as a
proper signed-off-patch?

Thanks.

-- 
tejun