linux-kernel - Re: [PATCH 6/6] freezer: kill unused set_freezable_with

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Message-ID: <20110911013742.GJ29319@htj.dyndns.org>
Date:	Sun, 11 Sep 2011 10:37:42 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, rjw@...k.pl, paul@...lmenage.org,
	containers@...ts.linux-foundation.org,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] freezer: kill unused set_freezable_with_signal()

Hello, Matt.

On Thu, Sep 08, 2011 at 11:01:59AM -0700, Matt Helsley wrote:
> Looking at the code and docs I realize I didn't explicitly mention that
> kthreads could not be frozen by the cgroup freezer. However, the code did
> not allow it. When freezing tasks the cgroup freezer always did:
> 
> 	freeze_task(task, true)
> 
> which would only freeze tasks without PF_FREEZER_NOSIG due to the second
> "sig_only" parameter. I believe this means it could not be used to
> freeze kthreads.
> 
> My feeling is kthreads should not be "managed" directly by userspace.
> Especially if that includes the ability to arbitrarily stop or freeze them.
> So it seems more appropriate to explicitly disallow freezing of kthreads
> via the cgroup freezer.

Oh yeah, that's what we should do and maybe that's what the current
code intends to achieve too but currently it ends up triggering
BUG_ON().

Thanks.

-- 
tejun
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