netdev - Re: PROBLEM: Silent data corruption when using sendfile()

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Date:	Sat, 14 Jul 2012 10:31:36 +0200
From:	Willy Tarreau <w@....eu>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Hillf Danton <dhillf@...il.com>,
	Johannes Truschnigg <johannes@...schnigg.info>,
	linux-kernel@...r.kernel.org, Linux-Netdev <netdev@...r.kernel.org>
Subject: Re: PROBLEM: Silent data corruption when using sendfile()

On Sat, Jul 14, 2012 at 10:20:41AM +0200, Eric Dumazet wrote:
> > On Tue, Jul 3, 2012 at 8:02 AM, Willy Tarreau <w@....eu> wrote:
> > >
> > > In fact it has been true zero copy in 2.6.25 until we faced a large
> > > amount of data corruption and the zero copy was disabled in 2.6.25.X.
> > > Since then it remained that way until you brought your patches to
> > > re-instantiate it.
> 
> Might be, or not (could be a NIC bug)

I may be wrong but what I recall from this bug was an issue when
forwarding TCP between two NICs, related to linear vs non-linear
data (I have memories of something around data not yet ACKed being
replaced before being retransmitted but I may be wrong). Anyway,
the way it was fixed consisted in simply disabling the zero-copy
code path. So this should be something different from what Johannes
reports. Maybe a regression since then though.

> Please Johannes could you try latest kernel tree ?

It would be useful, especially given the amount of changes you performed
in this area in latest version, it could be very possible that this new
bug got fixed as a side effect !

Regards,
Willy

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