linux-kernel - Re: [PATCH RFC v2] PM / sleep: Fix racing timers

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Date:	Mon, 28 Jul 2014 08:51:18 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Pavel Machek <pavel@....cz>
CC:	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH RFC v2] PM / sleep: Fix racing timers

On Mon, 2014-07-28 at 12:05PM +0200, Pavel Machek wrote:
> On Fri 2014-07-25 14:06:48, 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@...inx.com>
> 
> Did you test the hibernation?
No, I don't have a system to test hibernation. Suspend seems to work
fine though.

	Sören
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