linux-kernel - Re: [PATCH] memcg: do not expose uninitialized mem_cgroup_per

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Date:	Wed, 27 Jul 2011 09:58:45 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Igor Mammedov <imammedo@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>,
	linux-kernel@...r.kernel.org, balbir@...ux.vnet.ibm.com,
	linux-mm@...ck.org, Paul Menage <menage@...gle.com>,
	Li Zefan <lizf@...fujitsu.com>,
	containers@...ts.linux-foundation.org,
	Tim Deegan <Tim.Deegan@...rix.com>
Subject: Re: [PATCH] memcg: do not expose uninitialized mem_cgroup_per_node
 to world

On Tue 26-07-11 14:17:54, Andrew Morton wrote:
> On Fri, 10 Jun 2011 18:57:40 +0200
> Igor Mammedov <imammedo@...hat.com> wrote:
> 
> > On 06/08/2011 11:09 PM, Andrew Morton wrote:
> > > The original patch:
> > >
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -4707,7 +4707,6 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
> > >   	if (!pn)
> > >   		return 1;
> > >
> > > -	mem->info.nodeinfo[node] = pn;
> > >   	for (zone = 0; zone<  MAX_NR_ZONES; zone++) {
> > >   		mz =&pn->zoneinfo[zone];
> > >   		for_each_lru(l)
> > > @@ -4716,6 +4715,7 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
> > >   		mz->on_tree = false;
> > >   		mz->mem = mem;
> > >   	}
> > > +	mem->info.nodeinfo[node] = pn;
> > >   	return 0;
> > >   }
> > >
> > > looks like a really good idea.  But it needs a new changelog and I'd be
> > > a bit reluctant to merge it as it appears that the aptch removes our
> > > only known way of reproducing a bug.
> > >
> > > So for now I think I'll queue the patch up unchangelogged so the issue
> > > doesn't get forgotten about.
> > >
> > Problem was in rhel's xen hv.
> > It was missing fix for imul emulation.
> > Details here 
> > http://lists.xensource.com/archives/html/xen-devel/2011-06/msg00801.html
> > Thanks to Tim Deegan and everyone who was involved in the discussion.
> 
> I really don't want to trawl through a lengthy xen bug report

The bug turned out to be Xen specific and this patch just hidden the bug
in Xen.

> and write your changelog for you.
> 
> We still have no changelog for this patch.  Please send one.

Appart from a better programming style is there any other reason for
taking it?  If applied it might hide potential bugs when somebody is
touching data too early.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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