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

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Date:	Tue, 9 Sep 2014 22:21:05 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen

On Tue, Sep 9, 2014 at 1:48 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Wednesday, September 10, 2014 12:23:36 AM Tejun Heo wrote:
>> On Tue, Sep 09, 2014 at 05:16:55PM +0200, Michal Hocko wrote:
>> > But OOM killer doesn't kill kernel threads as they do not own any
>> > memory. So the check should be safe, no?
>>
>> Even for userland tasks, try_to_freeze() can currently be anywhere in
>> the kernel.  The frequently used ones are few but there are some odd
>> ones out, and, again, there's nothing enforcing any structure on
>> try_to_freeze() usage.  The other thing is that we may do quite a bit
>> during exiting including allocating memory.  Are those safe for system
>> PM?  Rafael, what exactly are the rules for PM?  What shouldn't
>> change?
>
> We can't make any assumptions regarding the availability of any devices.
> That is, whatever can end up in device access may potentially fail.
>

So we still have to rule out PM freeze, right?

I am thinking about adding a new task flag or adding a new parameter
to __refrigerator() to distinguish PM freeze with cgroup freeze. Will try
to code tomorrow.

Thanks!
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