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

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Date:   Thu, 21 Feb 2019 10:35:30 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Vincent Guittot <vincent.guittot@...aro.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, 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.

> 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!