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Message-ID: <1533198478.11791.10.camel@gmx.de>
Subject: Re: cpu stopper threads and setaffinity leads to deadlock
From:   Mike Galbraith <efault@gmx.de>
To:     Peter Zijlstra <peterz@infradead.org>,
        Sodagudi Prasad <psodagud@codeaurora.org>
Cc:     mingo@kernel.org, gregkh@linuxfoundation.org,
        bigeasy@linutronix.de, tglx@linutronix.de, isaacm@codeaurora.org,
        linux-kernel@vger.kernel.org
Date:   Thu, 02 Aug 2018 10:27:58 +0200
In-Reply-To: <20180802081252.GG2494@hirez.programming.kicks-ass.net>
References: <24eebe1d874cb8e3b9a18087554544fa@codeaurora.org>
         <20180802081252.GG2494@hirez.programming.kicks-ass.net>
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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);