linux-kernel - Re: [PATCH] kernel/hung_task.c: disable on suspend

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Date:   Fri, 21 Sep 2018 15:11:00 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] kernel/hung_task.c: disable on suspend

Oleg Nesterov <oleg@...hat.com> writes:

> On 09/17, Rafael J. Wysocki wrote:
>>
>> On Fri, Sep 14, 2018 at 6:21 PM Oleg Nesterov <oleg@...hat.com> wrote:
>> >
>> > > > 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 ;)
>>
>> Why would it be questionable?
>>
>> The watchdog needs to be disarmed somehow before tasks are frozen and
>> re-armed after they have been thawed or it may report false-positives
>> on the way out.  PM notifiers can be used for that.
>
> Or watchdog() can simply use set_freezable/freezing interface we already
> have, without additional complications.
>
> Yes, this is not "before tasks are frozen", but probably should work?
>
> OK, I won't argue.

I was hoping you and Rafael will come to an agreement but the discussion
just died ... so where do we stand on this? I see the following options:

1) The v1 patch is good, no freezing/disabling/parking required.
2) Make the kthread freezable (btw, I tested your patch and it seems to
work).
3) kthread_stop/kthread_run() (as you said 'no parking').
4) Drop the patch and wait for the root cause (increasing jiffies) to
dissolve.
5) ???

Ideas?

-- 
  Vitaly