Messages in this thread | | | Date | Thu, 24 Jul 2014 08:59:55 -0700 | From | Sören Brinkmann <> | Subject | Re: [PATCH RFC] suspend/hibernation: Fix racing timers |
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Hi John,
On Wed, 2014-07-23 at 08:55PM -0700, John Stultz wrote: > On 07/21/2014 10:35 AM, 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() > > -> 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 remove the timekeeping suspend/resume functions from > > the syscore functions and explictly call them at the appropriate time in > > the suspend/hibernation patchs. I.e. timers are suspend _before_ IRQs > > get disabled. And accordingly in the resume path. > > So.. I sort of follow this, though from the description disabling > timekeeping to turn off timers seems a little indirect (I do see that > suspending timekeeping calls clockevents_suspend() which is the key > part). Maybe this could be clarified in a future version of the patch > description? > > I worry that moving timekeeping_suspend earlier in the suspend process > might cause problems where things access time in the suspend path. I > recall these orderings have been problematic in the past, and slightly > tweaking them can often destabilize things badly.
You're right. Just when I received this I started seeing some warning from the kernel due to ktime_get() called with timekeeping being suspended. Though, stability-wise it seems to work.
> > I wonder if it would be better just to move the clockevent_suspend() > call to the earlier site, that way timers are halted but timekeeping > continues until its normal suspend point.
I'll look into this and send out a patch once I have something working.
Thanks, Sören -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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