linux-kernel - Re: [PATCH v2] powerpc/32: fix csum_partial_copy

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Date:	Fri, 5 Aug 2016 09:26:41 +0200
From:	Christophe Leroy <christophe.leroy@....fr>
To:	Michael Ellerman <mpe@...erman.id.au>,
	Alessio Igor Bogani <alessio.bogani@...ttra.eu>,
	Scott Wood <oss@...error.net>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...ts.ozlabs.org, stable@...r.kernel.org,
	antoine.blangy@....fr, segher@...nel.crashing.org
Subject: Re: [PATCH v2] powerpc/32: fix csum_partial_copy_generic()



Le 05/08/2016 à 08:57, Michael Ellerman a écrit :
> Alessio Igor Bogani <alessio.bogani@...ttra.eu> writes:
>> On 4 August 2016 at 05:53, Scott Wood <oss@...error.net> wrote:
>>> On Tue, 2016-08-02 at 10:07 +0200, Christophe Leroy wrote:
>>>> commit 7aef4136566b0 ("powerpc32: rewrite csum_partial_copy_generic()
>>>> based on copy_tofrom_user()") introduced a bug when destination
>>>> address is odd and initial csum is not null
>>>>
>>>> In that (rare) case the initial csum value has to be rotated one byte
>>>> as well as the resulting value is
>>>>
>>>> This patch also fixes related comments
>>>>
>>>> Fixes: 7aef4136566b0 ("powerpc32: rewrite csum_partial_copy_generic()
>>>> based on copy_tofrom_user()")
>>>> Cc: stable@...r.kernel.org
>>>>
>>>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>>>> ---
>>>>   v2: updated comments as suggested by Segher
>>>>
>>>>   arch/powerpc/lib/checksum_32.S | 7 ++++---
>>>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>> Alessio, can you confirm whether this fixes the problem you reported?
>> No unfortunately.
> Thanks for testing.
>
> I've dropped the patch for now, send me a new one that works.
>
>

The purpose of this patch was not to address Alessio's issue, but to fix 
a huge issue on checksum calculation which induces breakdown of TCP 
connections.

I think it is worth commiting it upstream and on impacted stable 
releases, allthought we don't have yet identified the issue Alessio's has.

Christophe