linux-kernel - Re: [PATCH 1/8] cgroup: kill cgroup_subsys->__DEPRECATED_clear_css

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Date:	Wed, 31 Oct 2012 10:22:37 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	lizefan@...wei.com, hannes@...xchg.org, bsingharora@...il.com,
	kamezawa.hiroyu@...fujitsu.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] cgroup: kill
 cgroup_subsys->__DEPRECATED_clear_css_refs

Hey, Michal.

On Wed, Oct 31, 2012 at 05:48:55PM +0100, Michal Hocko wrote:
> > The WARN_ON_ONCE() is just moved from the original
> > cgroup_call_pre_destroy().  We can add an error out there but that
> > makes future changes difficult.  It's a chicken and egg problem.  You
> > gotta break the loop somewhere.
> 
> I do not think this is that hard. You can simply change the return path
> on pre_destroy error by BUG_ON in "cgroup: deactivate CSS's and mark
> cgroup dead before invoking ->pre_destroy()". There is no chicke&egg
> problem here because once the group is marked dead and css frozen then
> the existing callbacks cannot possibly fail.
> Or am I missing your point?

I want to be able to move code verbatim in the later patch when
relocating ->pre_destroy() invocations.  Hmmm... alright, I'll make it
break out of pre_destroy() here and change it to WARN_ON_ONCE() later
on.

Thanks.

-- 
tejun
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