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

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Date:   Thu, 02 Aug 2018 10:27:58 +0200
From:   Mike Galbraith <efault@....de>
To:     Peter Zijlstra <peterz@...radead.org>,
        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 Thu, 2018-08-02 at 10:12 +0200, Peter Zijlstra wrote:
> 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.

Yup, one you fixed.

0b26351b910fb (Peter Zijlstra 2018-04-20 11:50:05 +0200 92)     wake_up_q(&wakeq);