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Date:	Mon, 28 Jul 2014 01:18:35 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Soren Brinkmann <soren.brinkmann@...inx.com>,
	John Stultz <john.stultz@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Pavel Machek <pavel@....cz>,
	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 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@...inx.com>
> ---
> 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?


>  kernel/power/hibernate.c  | 9 +++++++++
>  kernel/power/suspend.c    | 5 +++++
>  kernel/time/timekeeping.c | 1 -
>  3 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index fcc2611d3f14..ab9f807e2ccb 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -285,6 +285,8 @@ static int create_image(int platform_mode)
>  	if (error || hibernation_test(TEST_CPUS))
>  		goto Enable_cpus;
>  
> +	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
> +
>  	local_irq_disable();
>  
>  	error = syscore_suspend();
> @@ -316,6 +318,7 @@ static int create_image(int platform_mode)
>  	syscore_resume();
>  
>   Enable_irqs:
> +	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);
>  	local_irq_enable();
>  
>   Enable_cpus:
> @@ -440,6 +443,8 @@ static int resume_target_kernel(bool platform_mode)
>  	if (error)
>  		goto Enable_cpus;
>  
> +	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
> +
>  	local_irq_disable();
>  
>  	error = syscore_suspend();
> @@ -474,6 +479,7 @@ static int resume_target_kernel(bool platform_mode)
>  	syscore_resume();
>  
>   Enable_irqs:
> +	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);
>  	local_irq_enable();
>  
>   Enable_cpus:
> @@ -555,6 +561,8 @@ int hibernation_platform_enter(void)
>  	if (error)
>  		goto Platform_finish;
>  
> +	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
> +
>  	local_irq_disable();
>  	syscore_suspend();
>  	if (pm_wakeup_pending()) {
> @@ -568,6 +576,7 @@ int hibernation_platform_enter(void)
>  
>   Power_up:
>  	syscore_resume();
> +	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);
>  	local_irq_enable();
>  	enable_nonboot_cpus();
>  
> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> index ed35a4790afe..ca6c56a87ea3 100644
> --- a/kernel/power/suspend.c
> +++ b/kernel/power/suspend.c
> @@ -12,6 +12,7 @@
>  #include <linux/delay.h>
>  #include <linux/errno.h>
>  #include <linux/init.h>
> +#include <linux/clockchips.h>
>  #include <linux/console.h>
>  #include <linux/cpu.h>
>  #include <linux/cpuidle.h>
> @@ -253,6 +254,8 @@ static int suspend_enter(suspend_state_t state, bool *wakeup)
>  	if (error || suspend_test(TEST_CPUS))
>  		goto Enable_cpus;
>  
> +	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
> +
>  	arch_suspend_disable_irqs();
>  	BUG_ON(!irqs_disabled());
>  
> @@ -270,6 +273,8 @@ static int suspend_enter(suspend_state_t state, bool *wakeup)
>  		syscore_resume();
>  	}
>  
> +	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);
> +
>  	arch_suspend_enable_irqs();
>  	BUG_ON(irqs_disabled());
>  
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 32d8d6aaedb8..d2f21cbe2bfd 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1032,7 +1032,6 @@ static int timekeeping_suspend(void)
>  	write_seqcount_end(&timekeeper_seq);
>  	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
>  
> -	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
>  	clocksource_suspend();
>  	clockevents_suspend();
>  
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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