Re: [PATCH 2/5] PM / Runtime: Do not run callbacks under lock forpower.irq_safe set
From: Ming Lei
Date: Thu Sep 15 2011 - 06:55:45 EST
On Thu, Sep 15, 2011 at 4:45 AM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
> On Wednesday, September 14, 2011, Ming Lei wrote:
>> Hi,
>>
>> On Wed, Sep 14, 2011 at 12:06 AM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
>>
>> >> >> If power.lock is released, the transition states(resuming or suspending)
>> >> >
>> >> >> may be observed in rpm_suspend or rpm_resume, then tasks schedule
>> >> >
>> >> >> will be produced in these two functions,
>> >> >
>> >> > I don't think so, because the interrupts are still off.
>> >>
>> >> Yes, the interrupts are still off on local CPU, but the release of spin lock may
>> >> cause another CPUs to run into rpm_suspend or rpm_resume and produce
>> >> task schedule inside the two functions.
>> >
>> > Not for the same device, though.
>>
>> I think it is probable to happen on the same device in theory, see below:
>>
>> - suppose irq_safe is set before calling two pm_runtime_suspend below
>> - suppose this patch has been applied
>>
>> CPU0 CPU1
>> pm_runtime_suspend
>> acquired power lock
>> rpm_suspend
>> pm_runtime_suspend
>> spining power lock
>> ...
>> release power lock
>> acquired power lock
>> run .runtime_suspend
>> found the dev suspending
>> wait for power state and schedule
>
> OK, I see what the problem is. The second CPU can see the status
> being RPM_SUSPENDING in the irq_safe case, which isn't possible
> without the patch.
>
> Good catch!
>
> I think in that case rpm_suspend() should just release the lock,
> run cpu_relax(), reacquire the lock and go to the "repeat" label.
Yes, it makes sense in this case.
BTW: looks like something is wrong about PM mail list, I often got
the messages below these days:
Delivery to the following recipient has been delayed:
linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx
Message will be retried for 1 more day(s)
thanks,
--
Ming Lei
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