linux-kernel - Re: [PATCH] slab+slob: dup name string

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Message-ID: <4FBCFBE0.2080803@parallels.com>
Date:	Wed, 23 May 2012 19:01:52 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	David Rientjes <rientjes@...gle.com>,
	<linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
	<linux-mm@...ck.org>, Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH] slab+slob: dup name string

On 05/23/2012 06:48 PM, Christoph Lameter wrote:
> On Wed, 23 May 2012, James Bottomley wrote:
>
>>>> So, why not simply patch slab to rely on the string lifetime being the
>>>> cache lifetime (or beyond) and therefore not having it take a copy?
>
> Well thats they way it was for a long time. There must be some reason that
> someone started to add this copying business....  Pekka?
>

 From git:

commit 84c1cf62465e2fb0a692620dcfeb52323ab03d48
Author: Pekka Enberg <penberg@...nel.org>
Date:   Tue Sep 14 23:21:12 2010 +0300

SLUB: Fix merged slab cache names

As explained by Linus "I'm Proud to be an American" Torvalds:

Looking at the merging code, I actually think it's totally
buggy. If you have something like this:

  - load module A: create slab cache A

  - load module B: create slab cache B that can merge with A

  - unload module A

  - "cat /proc/slabinfo": BOOM. Oops.

exactly because the name is not handled correctly, and you'll have
module B holding open a slab cache that has a name pointer that points
to module A that no longer exists.

So if I understand it correctly, this is mostly because the name string 
outlives the cache in the slub case, because of merging ?
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