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

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Message-Id: <20130805141609.777a0d6dee55091f6981c39b@linux-foundation.org>
Date:	Mon, 5 Aug 2013 14:16:09 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrew Vagin <avagin@...allels.com>
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 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!

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?

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