Re: cpu stopper threads and setaffinity leads to deadlock

[Peter Zijlstra]

On Wed, Aug 01, 2018 at 06:34:40PM -0700, Sodagudi Prasad wrote:
> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> index e190d1e..f932e1e 100644
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -87,9 +87,9 @@ static bool cpu_stop_queue_work(unsigned int cpu, struct
> cpu_stop_work *work)
>                 __cpu_stop_queue_work(stopper, work, &wakeq);
>         else if (work->done)
>                 cpu_stop_signal_done(work->done);
> -       raw_spin_unlock_irqrestore(&stopper->lock, flags);
> 
>         wake_up_q(&wakeq);
> +       raw_spin_unlock_irqrestore(&stopper->lock, flags);
> 

That puts the wakeup back under stopper lock, which causes another
deadlock iirc.