Re: [PATCH 1/8] PM: Add suspend block api.
From: Arve Hjønnevåg
Date: Thu May 06 2010 - 19:48:47 EST
On Thu, May 6, 2010 at 12:40 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> On Thu, 6 May 2010, Rafael J. Wysocki wrote:
>
>> > Here's a completely new issue. When using opportunistic suspends on an
>> > SMP system, it could happen that the system gets a wakeup event and
>> > this routine starts running again before the event's IRQ handler has
>> > finished (or has enabled a suspend blocker). The system would
>> > re-suspend too soon.
>>
>> This routine will be run from a freezable workqueue.
>
> But how do you know that processes won't get unfrozen until all the
> pending IRQs have been handled? Imagine something like this:
>
> CPU 0 CPU 1
> ----- -----
> Wake up non-boot CPUs
> Resume devices Invoke the IRQ handler
>
> [ CPU 0 should wait here for the handler to finish,
> but it doesn't ]
>
> Defrost threads Handler running...
> Workqueue routine runs
> Start another suspend
> Handler enables a suspend blocker,
> but it's too late
It is not optimal, but it is not too late. We check if any suspend
blockers block suspend after disabling non-boot cpus so as long as
this is done in a way that does not lose interrupts the resuspend
attempt will not succeed.
--
Arve Hjønnevåg
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