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

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Message-ID: <fadb1f7b-82bf-4dbd-bfd4-ca24daca0a8f@BN1AFFO11FD060.protection.gbl>
Date:	Thu, 2 Oct 2014 09:01:15 -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,

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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