linux-kernel - Re: [RFC PATCH] freezer: allow killing of frozen tasks

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Message-ID: <CAH9JG2X3grVnUbuzksRLnDCT4dMQTyJuPa72qi4QmKTHo2QzEA@mail.gmail.com>
Date:	Wed, 25 Sep 2013 14:52:26 +0900
From:	Kyungmin Park <kmpark@...radead.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>, Tejun Heo <tj@...nel.org>
Cc:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Pavel Machek <pavel@....cz>, linux-pm@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Colin Cross <ccross@...roid.com>
Subject: Re: [RFC PATCH] freezer: allow killing of frozen tasks

On Tue, Aug 20, 2013 at 9:41 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Tuesday, August 20, 2013 08:27:27 AM Tejun Heo wrote:
>> On Tue, Aug 20, 2013 at 02:34:14PM +0200, Rafael J. Wysocki wrote:
>> > On Tuesday, August 20, 2013 08:22:00 AM Tejun Heo wrote:
>> > > On Tue, Aug 20, 2013 at 02:30:18PM +0200, Rafael J. Wysocki wrote:
>> > > > > So, I don't think we can simply turn TASK_UNITERRUPTIBLE to
>> > > > > TASK_KILLABLE at this point.  We really need to strictly define where
>> > > > > a task can freeze before being able to do anything like this.
>> > > >
>> > > > But we could do that for user space tasks I suppose?
>> > >
>> > > Even for userland tasks, we don't know where the task is stuck at.  I
>> > > think there are enough freeze points in the kernel which are in the
>> > > middle of something which can be used by userland tasks excuting some
>> > > syscall.  We need to collect all those sites into well defined trap
>> > > points before doing this.
>> >
>> > OK, thanks!
>>
>> I scanned through try_to_freeze() users and it seems like we don't
>> have that many which can be hit by userland tasks.  I think it should
>> be doable to audit all the users, remove the ones which can be invoked
>> by userland and make try_to_freeze() whine loudly if it's running off
>> a userland task except from well-defined spots.
>
> Which might be worth doing anyway to be sure we know what's going on.
>
>> Anyways, we need to ensure that userland task doesn't get stuck deep in the
>> kernel before allowing this.
>
> Agreed.

Are there any update? we need this feature to kill frozen app easily.
Don't need to thaw app to kill.

Thank you,
Kyungmin Park
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