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

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Date:	Mon, 8 Sep 2014 16:16:15 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
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 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. :)

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.
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