linux-kernel - Re: [PATCH 2/5] PM / Runtime: Do not run callbacks under lock for power.irq

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Date:	Thu, 15 Sep 2011 18:55:37 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Kevin Hilman <khilman@...com>, jean.pihet@...oldbits.com
Subject: Re: [PATCH 2/5] PM / Runtime: Do not run callbacks under lock for
 power.irq_safe set

On Thu, Sep 15, 2011 at 4:45 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Wednesday, September 14, 2011, Ming Lei wrote:
>> Hi,
>>
>> On Wed, Sep 14, 2011 at 12:06 AM, Rafael J. Wysocki <rjw@...k.pl> 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@...ts.linux-foundation.org

Message will be retried for 1 more day(s)


thanks,
-- 
Ming Lei
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