linux-kernel - Re: [BUG] SLOB breaks Crypto

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Date:	Tue, 18 May 2010 10:17:35 +0200
From:	Adrian-Ken Rueegsegger <ken@...elabs.ch>
To:	Matt Mackall <mpm@...enic.com>
CC:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	michael-dev@...i-braun.de, Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	Atsushi Nemoto <anemo@....ocn.ne.jp>
Subject: Re: [BUG] SLOB breaks Crypto

Matt Mackall schrieb:
> On Mon, 2010-05-17 at 23:50 +0200, Adrian-Ken Rueegsegger wrote:
>> Geert Uytterhoeven wrote:
>>> On Fri, Mar 19, 2010 at 02:33, Herbert Xu <herbert@...dor.apana.org.au> wrote:
>>>> On Thu, Mar 18, 2010 at 10:24:41PM +0100, michael-dev@...i-braun.de wrote:
>>>>> Pekka Enberg schrieb:
>>>>>> Even with CONFIG_DEBUG_SLAB enabled or with CONFIG_SLUB and
>>>>>> CONFIG_SLUB_DEBUG_ON?
>>>>> no, these options have not been / are not enabled.
>>>> Can you please try it with those options enabled? That will tell
>>>> us if there is some latent bug in the crypto layer that only shows
>>>> up right away under SLOB.
>>> After seeing a posting from Nemoto-san on the linux-mips list (should
>>> show up soon on
>>> http://www.linux-mips.org/archives/linux-mips/2010-05/threads.html),
>>> I'm wondering if these defaults are the culprit;
>>>
>>> mm/slab.c:#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)
>>> mm/slob.c:#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long)
>>> mm/slub.c:#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)
> 
> Seems the target here is x86, which has no DMA or other alignment
> constraints.
> 
>> Just a quick note: I changed this line in mm/slob.c to (unsigned long
>> long) and was able to load tcrypt without the kernel oopsing or
>> panic'ing. When running all test via
>>
>> modprobe tcrypt
> 
> Hmmm, sounds like something in crypto has a bogus alignment/padding
> expectation. Surprised it wasn't caught by SLAB redzoning though.
> Perhaps we can 'bisect' the test suite to narrow it down to a particular
> test. Alternately, we can tweak SLAB to offset buffers by two bytes and
> see what breaks.

As noted in my other mail [1] it seems like the HMAC tests trigger these
errors.

Regards,
Adrian

[1] - http://lkml.org/lkml/2010/5/14/199
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