linux-kernel - Re: [PATCH 1/3] cpuidle: coupled: disable interrupts after entering safe state

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Message-ID: <3891367.RzYTp6nikM@vostro.rjw.lan>
Date:	Thu, 29 Aug 2013 22:09:01 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Colin Cross <ccross@...roid.com>
Cc:	Prashant Gaikwad <pgaikwad@...dia.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Neil Zhang <zhangwm@...vell.com>,
	Joseph Lo <josephl@...dia.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 1/3] cpuidle: coupled: disable interrupts after entering safe state

On Thursday, August 29, 2013 12:12:17 AM Colin Cross wrote:
> On Wed, Aug 28, 2013 at 11:50 PM, Prashant Gaikwad <pgaikwad@...dia.com> wrote:
> > On Saturday 24 August 2013 01:15 AM, Colin Cross wrote:
> >>
> >> Calling cpuidle_enter_state is expected to return with interrupts
> >> enabled, but interrupts must be disabled before starting the
> >> ready loop synchronization stage.  Call local_irq_disable after
> >> each call to cpuidle_enter_state for the safe state.
> >>
> >> CC: stable@...r.kernel.org
> >> Signed-off-by: Colin Cross <ccross@...roid.com>
> >> ---
> >>   drivers/cpuidle/coupled.c | 2 ++
> >>   1 file changed, 2 insertions(+)
> >>
> >> diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
> >> index 2a297f8..db92bcb 100644
> >> --- a/drivers/cpuidle/coupled.c
> >> +++ b/drivers/cpuidle/coupled.c
> >> @@ -460,6 +460,7 @@ int cpuidle_enter_state_coupled(struct cpuidle_device
> >> *dev,
> >>                 }
> >>                 entered_state = cpuidle_enter_state(dev, drv,
> >>                         dev->safe_state_index);
> >> +               local_irq_disable();
> >
> >
> > Colin,
> >
> > There is still some window where irq remains enabled after exiting safe
> > state. It may introduce some corner case.
> > Instead of this can we pass a parameter to cpuidle_enter_state indicating
> > that irq has to be enabled or not after exit from idle state, which would be
> > false when entering safe state from coupled idle.
> 
> It's fine for irqs to be enabled when exiting the safe state, in fact
> on further inspection this patch isn't strictly necessary at all - we
> always enable interrupts inside cpuidle_coupled_clear_pokes soon after
> cpuidle_enter_state returns, and then disable them again.  It's
> probably better to disable interrupts right after cpuidle_enter_state,
> it makes sure interrupts are consistently disabled when calling
> cpuidle_coupled_set_waiting, cpuidle_coupled_cpus_waiting and
> cpuidle_coupled_clear_pokes, although that doesn't matter in the
> current implementation.
> 
> Rafael, feel free to drop the stable annotation from this patch.

I will, thanks!

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