From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Tejun Heo <tj@kernel.org>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Pavel Machek <pavel@ucw.cz>, linux-pm@vger.kernel.org,
        Kyungmin Park <kyungmin.park@samsung.com>,
        LKML <linux-kernel@vger.kernel.org>, Colin Cross <ccross@android.com>
Subject: Re: [RFC PATCH] freezer: allow killing of frozen tasks
Date: Tue, 20 Aug 2013 14:41:26 +0200
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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.

Thanks,
Rafael

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