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

From: John Stultz
Date: Mon Jul 28 2014 - 15:26:17 EST

On 07/27/2014 04:18 PM, Rafael J. Wysocki wrote:
> On Friday, July 25, 2014 02:06:48 PM 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@xxxxxxxxxx>
>> ---
>> Hi,
>> This is my second shot at this. I followed John's suggestion to keep the
>> timekeeping suspend where it is and just move the shutdown of the clockevent
>> devices around.
> John, what do you think?

I've not had the chance to take a closer look and do any testing. I
suspect we'll need tgxl's input here as well.

The change makes sense, but ordering modifications in this area tend to
be fragile, as there are lots of implicit dependencies.


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