Re: [PATCH v2] powerpc/32: fix csum_partial_copy_generic()

[Christophe Leroy]

Le 05/08/2016 à 08:57, Michael Ellerman a écrit :
> Alessio Igor Bogani <alessio.bogani@xxxxxxxxxx> writes:
> > On 4 August 2016 at 05:53, Scott Wood <oss@xxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx
> > > >
> > > > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> > > > ---
> > > >   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