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Date: Tue, 28 Oct 2014 13:40:11 -0700
From: Sören Brinkmann <soren.brinkmann@...inx.com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
CC: Thomas Gleixner <tglx@...utronix.de>,
John Stultz <john.stultz@...aro.org>,
Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>
Subject: Re: [PATCH RESEND] PM / sleep: Fix racing timers
Hi Rafael,
any opinion on this?
Thanks,
Sören
On Thu, 2014-10-02 at 09:01AM -0700, Sören Brinkmann wrote:
> Hi Rafael,
>
> On Tue, 2014-09-23 at 01:01AM +0200, Rafael J. Wysocki wrote:
> > On Monday, September 22, 2014 10:07:03 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()
> > > -> 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>
> > > ---
> > > Hi,
> > >
> > > there was not a lot of discussion on the last submission. Just one comment from
> > > Rafael (https://lkml.org/lkml/2014/8/26/780), which - as I outlined in my
> > > response, does not apply, IMHO, since the platform does not re-enable
> > > interrupts.
> >
> > Well, you just don't agree with it.
> >
> > The problem with your approach is that timer interrupts aren't actually as
> > special as you think and any other IRQF_NO_SUSPEND interrupts would have caused
> > similar issues to appear under specific conditions.
> >
> > The solution I would suggest and that actually covers all IRQF_NO_SUSPEND
> > interrupts would be to use a wait_event() loop like the one in freeze_enter()
> > (on top of the current linux-next or the pm-genirq branch of linux-pm.git),
> > but wait for pm_abort_suspend to become true, to implement system suspend.
>
> sorry, it took me a while since I needed to get some dependencies ported
> to the pm-genirq base. Once I had that, it reproduced my original issue.
> So far so good. I then looked into finding a solution following your
> guidance. I'm not sure I really found what you had in mind, but below is
> what I came up with, which seems to do it.
> Please let me know how far off I am.
>
> Thanks,
> Sören
>
> -------8<------------------8<----------------8<----------------8<---------------
> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> index c2744b30d5d9..a4f9914571f1 100644
> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -25,7 +25,7 @@
> bool events_check_enabled __read_mostly;
>
> /* If set and the system is suspending, terminate the suspend. */
> -static bool pm_abort_suspend __read_mostly;
> +bool pm_abort_suspend __read_mostly;
>
> /*
> * Combined counters of registered wakeup events and wakeup events in progress.
> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> index 6dadb25cb0d8..e6a6de8f76d0 100644
> --- a/kernel/power/suspend.c
> +++ b/kernel/power/suspend.c
> @@ -33,6 +33,7 @@
>
> static const char *pm_labels[] = { "mem", "standby", "freeze", };
> const char *pm_states[PM_SUSPEND_MAX];
> +extern bool pm_abort_suspend;
>
> static const struct platform_suspend_ops *suspend_ops;
> static const struct platform_freeze_ops *freeze_ops;
> @@ -294,25 +295,27 @@ static int suspend_enter(suspend_state_t state, bool *wakeup)
> if (error || suspend_test(TEST_CPUS))
> goto Enable_cpus;
>
> - arch_suspend_disable_irqs();
> - BUG_ON(!irqs_disabled());
> -
> - error = syscore_suspend();
> - if (!error) {
> - *wakeup = pm_wakeup_pending();
> - if (!(suspend_test(TEST_CORE) || *wakeup)) {
> - trace_suspend_resume(TPS("machine_suspend"),
> - state, true);
> - error = suspend_ops->enter(state);
> - trace_suspend_resume(TPS("machine_suspend"),
> - state, false);
> - events_check_enabled = false;
> + while (!pm_abort_suspend) {
> + arch_suspend_disable_irqs();
> + BUG_ON(!irqs_disabled());
> +
> + error = syscore_suspend();
> + if (!error) {
> + *wakeup = pm_wakeup_pending();
> + if (!(suspend_test(TEST_CORE) || *wakeup)) {
> + trace_suspend_resume(TPS("machine_suspend"),
> + state, true);
> + error = suspend_ops->enter(state);
> + trace_suspend_resume(TPS("machine_suspend"),
> + state, false);
> + events_check_enabled = false;
> + }
> + syscore_resume();
> }
> - syscore_resume();
> - }
>
> - arch_suspend_enable_irqs();
> - BUG_ON(irqs_disabled());
> + arch_suspend_enable_irqs();
> + BUG_ON(irqs_disabled());
> + }
>
> Enable_cpus:
> enable_nonboot_cpus();
> --
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