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Date: Mon, 28 Jul 2014 12:19:22 -0700
From: Stephen Boyd <sboyd@codeaurora.org>
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To: Soren Brinkmann <soren.brinkmann@xilinx.com>
CC: John Stultz <john.stultz@linaro.org>, Thomas Gleixner <tglx@linutronix.de>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, Pavel Machek <pavel@ucw.cz>,
        Len Brown <len.brown@intel.com>, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org, Daniel Lezcano <daniel.lezcano@linaro.org>
Subject: Re: [PATCH RFC v2] PM / sleep: Fix racing timers
References: <53D083C5.2000501@linaro.org> <1406322408-15408-1-git-send-email-soren.brinkmann@xilinx.com>
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On 07/25/14 14:06, Soren Brinkmann wrote:
> On platforms that do not power off during suspend, successfully entering
> suspend races with timers.
>
> The race happening in a couple of location is:
>
>   1. disable IRQs   		(e.g. arch_suspend_disable_irqs())
>      ...
>   2. syscore_suspend()
>       -> timekeeping_suspend()
>        -> clockevents_notify(SUSPEND)
>         -> tick_suspend()   	(timers are turned off here)
>      ...
>   3. wfi            		(wait for wake-IRQ here)
>
> Between steps 1 and 2 the timers can still generate interrupts that are
> not handled and stay pending until step 3. That pending IRQ causes an
> immediate - spurious - wake.
>
> The solution is to move the clockevents suspend/resume notification
> out of the syscore_suspend step and explictly call them at the appropriate
> time in the suspend/hibernation paths. I.e. timers are suspend _before_
> IRQs get disabled. And accordingly in the resume path.
>
> Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>

Do we know which timer_list or hrtimer wants to run while entering
suspend? I'd suspect the scheduler tick but perhaps we just forgot to
cancel some timer during suspend?

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