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

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Message-ID: <CAM_iQpUbGTxrbJZ_ztf+QUvFowsivQ-jvPCSi7kmth7nstPvaA@mail.gmail.com>
Date:	Fri, 5 Sep 2014 11:12:24 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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 11:00 AM, Tejun Heo <tj@...nel.org> wrote:
> On Fri, Sep 05, 2014 at 09:31:50AM -0700, Cong Wang wrote:
>> On Fri, Sep 5, 2014 at 7:08 AM, Tejun Heo <tj@...nel.org> wrote:
>> >> +     /* It might not be safe to check TIF_MEMDIE for pm freeze. */
>> >
>> > This is just another representation of the following code which isn't
>> > particularly useful.  Wouldn't it be better if the comment actually
>> > explains why this might not be safe?
>>
>> I don't know actually, I never understand pm code, just don't
>> want to take the risk of breaking it as you told. :)
>
> Let's please try to understand and explain it properly.  Reading
> intricate code like this w/ comment which doesn't really explain
> anything can be very frustrating for other people reading the code.

That comment just explains why we need a cgroup_freezing() check,
nothing else. If you don't think it helps, I can definitely remove it.

> Rafael, can you please help?

Rafael is known not responsive at least for this topic. :)

>
> 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.
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