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

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Message-ID: <37238430.gCktWD5jr4@vostro.rjw.lan>
Date:	Tue, 20 Aug 2013 14:30:18 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Tejun Heo <tj@...nel.org>
Cc:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Pavel Machek <pavel@....cz>, linux-pm@...r.kernel.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Colin Cross <ccross@...roid.com>
Subject: Re: [RFC PATCH] freezer: allow killing of frozen tasks

On Tuesday, August 20, 2013 08:18:19 AM Tejun Heo wrote:
> Hello,
> 
> On Tue, Aug 20, 2013 at 02:23:32PM +0200, Rafael J. Wysocki wrote:
> > On Tuesday, August 20, 2013 01:20:03 PM Bartlomiej Zolnierkiewicz wrote:
> > > Change __refrigerator() to allow SIGKILL signal handling during
> > > the frozen state (by setting task to a TASK_KILLABLE state instead
> > > of TASK_UNINTERRUPTIBLE one before entering sleep) and make tasks
> > > leave __refrigerator() upon receiving such signal.
> > > 
> > > These changes allow frozen tasks to be killed immediately without
> > > the need to thaw them first.
> > > 
> > > Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
> > > Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
> > 
> > Well, it doesn't sound like an entirely bad idea to me, but I'd like to know
> > what Colin and Tejun (CCed now) think about it.
> 
> The problem is that we really don't know where each task is frozen in
> the kernel so don't know what happens after the task leaves the
> freezer is safe whether it's dying or not.  We don't have any rules
> restricting where a freeze point should be and a task may do any
> operation between freezer and actual exit.
> 
> 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?

Rafael

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