linux-kernel - Re: [PATCH] PM-runtime: fix deadlock when canceling hrtimer

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Date:   Thu, 21 Feb 2019 11:02:23 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Zhaosheng Sun <sunzhaosheng@...ilicon.com>
Subject: Re: [PATCH] PM-runtime: fix deadlock when canceling hrtimer

On Thu, 21 Feb 2019 at 10:35, Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Feb 21, 2019 at 8:59 AM Vincent Guittot
> <vincent.guittot@...aro.org> wrote:
> >
> > When rpm_resume() desactivates the autosuspend timer, it should only try
> > to cancel hrtimer but not wait for the handler to finish because both
> > rpm_resume() and pm_suspend_timer_fn() are taking the power.lock.
> > We can have the deadlock sequence:
> > CPU0                              CPU1
> > rpm_resume()
> >   spin_lock_irqsave
> >                                   pm_suspend_timer_fn()
> >                                     spin_lock_irqsave
> >   pm_runtime_deactivate_timer()
> >     hrtimer_cancel()
>
> Everybody has missed this, not good.

yes. default behavior if different between timer and hrtimer
del_timer() is equivalent to hrtimer_try_to_cancel()
and hrtimer_cancel() to del_timer_sync()

>
> > hrtimer_try_to_cancel() is enough because dev->power.timer_expires is also
> > set to 0.
> >
> > Fixes: 8234f6734c5d ("PM-runtime: Switch autosuspend over to using hrtimers")
> > Reported-by: Sunzhaosheng Sun(Zhaosheng) <sunzhaosheng@...ilicon.com>
> > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> > ---
> >  drivers/base/power/runtime.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> > index 04407d9..78937c4 100644
> > --- a/drivers/base/power/runtime.c
> > +++ b/drivers/base/power/runtime.c
> > @@ -121,7 +121,7 @@ EXPORT_SYMBOL_GPL(pm_runtime_suspended_time);
> >  static void pm_runtime_deactivate_timer(struct device *dev)
> >  {
> >         if (dev->power.timer_expires > 0) {
> > -               hrtimer_cancel(&dev->power.suspend_timer);
> > +               hrtimer_try_to_cancel(&dev->power.suspend_timer);
> >                 dev->power.timer_expires = 0;
> >         }
> >  }
> > --
>
> Applied with some changelog modifications, thanks!

Thanks