linux-kernel - Re: mm: slub: invalid memory access in setup

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Date:	Wed, 2 Jul 2014 10:06:46 +0800
From:	Wei Yang <weiyang@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...two.org>,
	David Rientjes <rientjes@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Wei Yang <weiyang@...ux.vnet.ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: mm: slub: invalid memory access in setup_object

On Tue, Jul 01, 2014 at 02:49:47PM -0700, Andrew Morton wrote:
>On Tue, 1 Jul 2014 09:58:52 -0500 (CDT) Christoph Lameter <cl@...two.org> wrote:
>
>> On Mon, 30 Jun 2014, David Rientjes wrote:
>> 
>> > It's not at all clear to me that that patch is correct.  Wei?
>> 
>> Looks ok to me. But I do not like the convoluted code in new_slab() which
>> Wei's patch does not make easier to read. Makes it difficult for the
>> reader to see whats going on.
>> 
>> Lets drop the use of the variable named "last".
>> 
>> 
>> Subject: slub: Only call setup_object once for each object
>> 
>> Modify the logic for object initialization to be less convoluted
>> and initialize an object only once.
>> 
>
>Well, um.  Wei's changelog was much better:
>
>: When a kmem_cache is created with ctor, each object in the kmem_cache will
>: be initialized before use.  In the slub implementation, the first object
>: will be initialized twice.
>: 
>: This patch avoids the duplication of initialization of the first object.
>: 
>: Fixes commit 7656c72b5a63: ("SLUB: add macros for scanning objects in a
>: slab").
>
>I can copy that text over and add the reported-by etc (ho hum) but I
>have a tiny feeling that this patch hasn't been rigorously tested? 
>Perhaps someone (Wei?) can do that?

Ok, I will apply this one and give a shot.

>
>And we still don't know why Sasha's kernel went oops.

Yep, if there is some procedure to reproduce it, I'd like to do it at my side.

-- 
Richard Yang
Help you, Help me

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