Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Thu, 2 Mar 2023 15:56:43 +0100 | Subject | Re: [RFC][PATCH 2/2] time: alarmtimer: Use TASK_FREEZABLE to cleanup freezer handling |
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On Thu, Mar 2, 2023 at 3:54 PM Rafael J. Wysocki <rafael@kernel.org> wrote: > > On Wed, Mar 1, 2023 at 11:11 PM Thomas Gleixner <tglx@linutronix.de> wrote: > > > > On Mon, Feb 27 2023 at 20:06, John Stultz wrote: > > > On Mon, Feb 27, 2023 at 4:03 PM John Stultz <jstultz@google.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? > > The pm_wakeup_event() doesn't need the timeout, but it is conditional > on using /sys/power/wakeup_count. > > However, in any case it doesn't guarantee that the target user of the > alarm timer will be able to handle the signal on time AFAICS. To my > eyes, it is entirely possible for alarmtimer_fired() to run before > /sys/power/wakeup_count is written to while the signal will be sent to
I actually should have said "read from" instead of "written to" here, sorry.
> the given task later, in which case there is no guarantee that the > task will not be frozen in the meantime. > > Moreover, I'm wondering if all alarm timers should always wake up the > system from sleep or abort suspends in progress? If the answer is > "no" here, it changes the problem at hand quite a bit.
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