linux-kernel - Re: [Patch v4 1/2] freezer: check OOM kill while being frozen

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Message-ID: <4809128.C6aPga5IjQ@vostro.rjw.lan>
Date:	Tue, 09 Sep 2014 01:42 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen

On Monday, September 08, 2014 04:16:15 PM Cong Wang wrote:
> On Mon, Sep 8, 2014 at 4:23 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >
> > The reason why it matters for the suspend-time freezing is that we freeze tasks
> > to take them out of the picture entirely until they are thawed.  Therefore we
> > can't allow them to go back to the picture just for a while until they are
> > killed.  Frozen tasks are not supposed to get back to the picture at all.
> >
> 
> 
> Ok, then checking TIF_MEMDIE is unsafe for PM freeze, we should
> keep the cgroup_freezing() test to make sure freeze request is from
> cgroup not PM. Question got answered. :)

Do I think correctly that cgroups freezing and system suspend are
mutually exclusive?  If not, then this still is problematic.

> I will put the following as a comment:
> 
> /* OOM killer may decide to kill this process after it is frozen,
>    in this case SIGKILL can never be handled, so we should check
>   TIF_MEMDIE and if it is set, thaw and let SIGKILL kill it.
>   But for PM freeze, it is not allowed to get out even for a while,
>   so we have to keep it being frozen. */
> 
> Let me know if it looks good to you.

Well, it reflects the reality, so it's good enough.  But please adhere to the
coding style rules for comments.

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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