linux-kernel - Re: [RFC][PATCH 2/2] time: alarmtimer: Use TASK

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Date:   Wed, 01 Mar 2023 23:11:50 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     John Stultz <jstultz@...gle.com>
Cc:     Michael Nazzareno Trimarchi <michael@...rulasolutions.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Michael <michael@...isi.de>, kernel-team@...roid.com,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [RFC][PATCH 2/2] time: alarmtimer: Use TASK_FREEZABLE to
 cleanup freezer handling

On Mon, Feb 27 2023 at 20:06, John Stultz wrote:
> On Mon, Feb 27, 2023 at 4:03 PM John Stultz <jstultz@...gle.com> wrote:
>> > On Mon, Feb 20 2023 at 19:11, Michael Nazzareno Trimarchi wrote:
>> > +static int alarmtimer_pm_notifier_fn(struct notifier_block *bl, unsigned long state,
>> > +                                    void *unused)
>> > +{
>> > +       switch (state) {
>> > +       case PM_HIBERNATION_PREPARE:
>> > +       case PM_POST_HIBERNATION:
>> > +               atomic_set(&alarmtimer_wakeup, 0);
>> > +               break;
>> > +       }
>> > +       return NOTIFY_DONE;
>>
>> But here, we're setting the alarmtimer_wakeup count to zero if we get
>> PM_HIBERNATION_PREPARE or  PM_POST_HIBERNATION notifications?
>> And Michael noted we need to add  PM_SUSPEND_PREPARE and
>> PM_POST_SUSPEND there for this to seemingly work.

Yup. I missed those when sending out that hack.

> So Thomas's notifier method of zeroing at the begining of suspend and
> tracking any wakeups after that point makes more sense now. It still
> feels a bit messy, but I'm not sure there's something better.

I'm not enthused about it either. 

> My only thought is this feels a little bit like its mirroring what the
> pm_wakeup_event() logic is supposed to do. Should we be adding a
> pm_wakeup_event() to alarmtimer_fired() to try to prevent suspend from
> occuring for 500ms or so after an alarmtimer has fired so there is
> enough time for it to be re-armed if needed?

The question is whether this can be called unconditionally and how that
interacts with the suspend logic. Rafael?

Thanks,

        tglx