linux-kernel - Re: cpu stopper threads and setaffinity leads to deadlock

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Date:   Thu, 2 Aug 2018 10:12:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sodagudi Prasad <psodagud@...eaurora.org>
Cc:     mingo@...nel.org, gregkh@...uxfoundation.org,
        bigeasy@...utronix.de, tglx@...utronix.de, isaacm@...eaurora.org,
        linux-kernel@...r.kernel.org
Subject: Re: cpu stopper threads and setaffinity leads to deadlock

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.