linux-kernel - Re: [PATCH] memcg: don't initialize kmem-cache destroying work for root caches

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Date:	Tue, 6 Aug 2013 01:41:35 +0400
From:	Andrew Vagin <avagin@...allels.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Andrey Vagin <avagin@...nvz.org>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Glauber Costa <glommer@...nvz.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH] memcg: don't initialize kmem-cache destroying work for
 root caches

On Mon, Aug 05, 2013 at 02:16:09PM -0700, Andrew Morton wrote:
> On Tue, 6 Aug 2013 01:01:28 +0400 Andrew Vagin <avagin@...allels.com> wrote:
> 
> > On Mon, Aug 05, 2013 at 01:05:30PM -0700, Andrew Morton wrote:
> > > On Mon,  5 Aug 2013 20:09:40 +0400 Andrey Vagin <avagin@...nvz.org> wrote:
> > > 
> > > > struct memcg_cache_params has a union. Different parts of this union
> > > > are used for root and non-root caches. A part with destroying work is
> > > > used only for non-root caches.
> > > > 
> > > > I fixed the same problem in another place v3.9-rc1-16204-gf101a94, but
> > > > didn't notice this one.
> > > > 
> > > > Cc: <stable@...r.kernel.org>    [3.9.x]
> > > 
> > > hm, why the cc:stable?
> > 
> > Because this patch fixes the kernel panic:
> > 
> > [   46.848187] BUG: unable to handle kernel paging request at 000000fffffffeb8
> > [   46.849026] IP: [<ffffffff811a484c>] kmem_cache_destroy_memcg_children+0x6c/0xc0
> > [   46.849092] PGD 0
> > [   46.849092] Oops: 0000 [#1] SMP
> 
> OK, pretty soon we'll have a changelog!

Sorry, probably I had to write all these in the initial commit message. I
just thought that this patch is an additional part of v3.9-rc1-16204-gf101a94.

> 
> What does one do to trigger this oops?  The bug has been there since
> 3.9, so the means-of-triggering must be quite special?

I don't think that so many people use cgroups with limits of the kernel memory.

I use the vzctl utility to operate with containers. vzctl limits the
kernel memory of containers by default. A container should be started
and stoped a few times (five or four) to reproduce the bug.

And one more thing is that nf_conntrack should be loaded. It creates
a new kmem_cache for each network namespace.

Thanks
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