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

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Message-ID: <2084875.Px2m8K6oH7@vostro.rjw.lan>
Date:	Wed, 25 Sep 2013 10:07:22 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Kyungmin Park <kmpark@...radead.org>
Cc:	Tejun Heo <tj@...nel.org>,
	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 Wednesday, September 25, 2013 02:52:26 PM Kyungmin Park wrote:
> 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.

No updates, but the above pretty much describes what needs to be done.

Thanks,
Rafael

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