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

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Message-ID: <87d0tg88l3.fsf@vitty.brq.redhat.com>
Date:   Fri, 14 Sep 2018 16:19:52 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] kernel/hung_task.c: disable on suspend

"Rafael J. Wysocki" <rjw@...ysocki.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?
>

We can either park the kthread (kthread_park/unpark) or make it go away
completely by doing kthread_stop/kthread_run(). I'm leaning toward
parking, what do you think?

-- 
  Vitaly