linux-kernel - Re: [patch 1/2] mm: memcontrol: handle potential crash when rmap races with task exit

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Message-ID: <20121005070521.GB27757@dhcp22.suse.cz>
Date:	Fri, 5 Oct 2012 09:05:21 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-mm@...ck.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] mm: memcontrol: handle potential crash when rmap
 races with task exit

On Thu 04-10-12 16:19:08, Johannes Weiner wrote:
> On Thu, Oct 04, 2012 at 08:49:58PM +0200, Michal Hocko wrote:
> > On Thu 04-10-12 14:09:16, Johannes Weiner wrote:
> > > page_referenced() counts only references of mm's that are associated
> > > with the memcg hierarchy that is being reclaimed.  However, if it
> > > races with the owner of the mm exiting, mm->owner may be NULL.  Don't
> > > crash, just ignore the reference.
> > 
> > This seems to be fixed by Hugh's patch 3a981f48 "memcg: fix use_hierarchy
> > css_is_ancestor oops regression" which seems to be merged already.
> 
> And look who acked the patch.  I'll show myself out...

My memory is a bit fuzzy but I remember we had two alternatives and
Hugh's won.

-- 
Michal Hocko
SUSE Labs
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