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SubjectRe: [PATCH] kernel/hung_task.c: disable on suspend
On 09/14, Vitaly Kuznetsov wrote:
>
> "Rafael J. Wysocki" <rjw@rjwysocki.net> writes:
>
> > On Thursday, September 13, 2018 6:08:51 PM CEST Vitaly Kuznetsov wrote:
> ...
>
> >> +static int hungtask_pm_notify(struct notifier_block *self,
> >> + unsigned long action, void *hcpu)
> >> +{
> >> + switch (action) {
> >> + case PM_SUSPEND_PREPARE:
> >> + case PM_HIBERNATION_PREPARE:
> >> + hung_detector_suspended = true;
> >> + break;
> >> + case PM_POST_SUSPEND:
> >> + case PM_POST_HIBERNATION:
> >> + hung_detector_suspended = false;
> >> + break;
> >> + default:
> >> + break;
> >> + }
> >> + return NOTIFY_OK;
> >> +}
> >> +
> >> /*
> >> * kthread which checks for tasks stuck in D state
> >> */
> >> @@ -261,7 +282,8 @@ static int watchdog(void *dummy)
> >> interval = min_t(unsigned long, interval, timeout);
> >> t = hung_timeout_jiffies(hung_last_checked, interval);
> >
> > Since you are adding the notifier anyway, what about designing it to make
> > the thread wait on _PREPARE until the notifier kicks it again on exit
> > fron suspend/hibernation?

Well. I agree that freezable kthreads are not nice, but it seems you are
going to add another questionable interface ;)

Vitaly, could you please update the changelog to explain in details whats
going on?

Where does the caller of pm_suspend() sleep in D state? Why it sleeps more
than 120 seconds?

And. given that it takes system_transition_mutex anyway, can't it use
lock_system_sleep() which marks the caller as PF_FREEZER_SKIP (checked
in check_hung_task()) ?

I have to admit I got lost...

> We can either park the kthread (kthread_park/unpark)

No, no, please don't. Nobody outside of smpboot.c should use this (and
this interface should be reworked). Yes, there are already abused, but
please don't add new users.

Oleg.

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