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

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Message-ID: <CAM_iQpXUDt1eM-R-Ofr3OzxjB=9K3JZ-XupJ916c7k_NzMK5WQ@mail.gmail.com>
Date:	Mon, 8 Sep 2014 10:40:17 -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 Fri, Sep 5, 2014 at 4:32 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Saturday, September 06, 2014 07:45:54 AM Tejun Heo wrote:
>> Hello,
>>
>> On Fri, Sep 05, 2014 at 11:12:24AM -0700, Cong Wang wrote:
>> > > Rafael, can you please help?
>> >
>> > Rafael is known not responsive at least for this topic. :)
>>
>> :(
>
> Well, am I?
>
> I haven't commented patches in this thread so far, mostly because other
> people have.
>
> How can I help actually?


We asked you to comment on either if this patch is safe for PM freeze
if we don't have the cgroup_freezing() check, or if it is not safe why (so that
I can put it in the comment).

>
>> > > Shouldn't the primary goal of the comment be explaining why we need
>> > > TIF_MEMDIE check there at all anyway?  The deadlock possiblity is not
>> > > very obvious.
>> >
>> > The changelog is not long enough?? ;-) I hate to copy+paste changelog
>> > into comments, changelog is essentially necessary for people to understand
>> > kernel code (at least networking) , so I don't think we have to move it
>> > into comments in this case.
>>
>> It doesn't have to be the same text but the current comment is
>> basically content-less.  e.g. it can just say "OOM killer may get
>> stuck trying to kill a cgroup frozen task" and actualy provide
>> information on what condition the conditional tries to address.
>
> Or something like "We need to check X to prevent Y from happening".
>

OK, maybe just one or two sentences. Let me know if the following
comment is okay for you:

/* OOM killer might decide to kill this process after it is frozen,
  in this case it should thaw and die. */

Thanks.
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