netdev - Re: [net PATCH 0/2] Don't use lco_csum to compute IPv4 checksum

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Date:   Thu, 12 Jan 2017 10:19:29 +1100
From:   Stephen Rothwell <sfr@...b.auug.org.au>
To:     davem@...emloft.net
Cc:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>, netdev@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Eli Cooper <elicooper@....com>,
        Lance Richardson <lrichard@...hat.com>,
        Sven-Haegar Koch <haegar@...net.de>
Subject: Re: [net PATCH 0/2] Don't use lco_csum to compute IPv4 checksum

Hi Dave,

On Tue, 29 Nov 2016 20:07:08 +1100 Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>
> Hi Jeff,
> 
> On Tue, 29 Nov 2016 10:43:04 +1100 Stephen Rothwell <sfr@...b.auug.org.au> wrote:
> >
> > On Mon, 28 Nov 2016 14:26:02 -0800 Jeff Kirsher <jeffrey.t.kirsher@...el.com> wrote:  
> > >
> > > On Mon, 2016-11-28 at 10:42 -0500, Alexander Duyck wrote:    
> > > > When I implemented the GSO partial support in the Intel drivers I was
> > > > using
> > > > lco_csum to compute the checksum that we needed to plug into the IPv4
> > > > checksum field in order to cancel out the data that was not a part of the
> > > > IPv4 header.  However this didn't take into account that the transport
> > > > offset might be pointing to the inner transport header.
> > > > 
> > > > Instead of using lco_csum I have just coded around it so that we can use
> > > > the outer IP header plus the IP header length to determine where we need
> > > > to
> > > > start our checksum and then just call csum_partial ourselves.
> > > > 
> > > > This should fix the SIT issue reported on igb interfaces as well as
> > > > simliar
> > > > issues that would pop up on other Intel NICs.
> > > > 
> > > > ---
> > > > 
> > > > Alexander Duyck (2):
> > > >       igb/igbvf: Don't use lco_csum to compute IPv4 checksum
> > > >       ixgbe/ixgbevf: Don't use lco_csum to compute IPv4 checksum      
> > > 
> > > Stephen, I have applied Alex's patches to my net-queue tree.  Can you
> > > confirm they resolve the bug seen?    
> > 
> > Its a bit tricky because the origin problem only happens on my
> > production server (ozlabs.org), but I will see if I can manage to just
> > remove and reload the driver ...  though, the server is running a 4.7.8
> > kernel and I am wondering how well these patches will apply?  
> 
> We have a winner!  This fixes my problem, so I can run at full speed
> with gso and tso enabled in the sit interface and tx-gso-partial
> enabled on the underlying ethernet.
> 
> Thanks to everyone for diagnosis and solution.
> 
> It would be nice if this fix went into the stable kernels as well so it
> will turn up in the distro kernels eventually.

It looks like these 2 commits:

516165a1e2f2	igb/igbvf: Don't use lco_csum to compute IPv4 checksum
c54cdc316dbd	ixgbe/ixgbevf: Don't use lco_csum to compute IPv4 checksum

have not been sent to stable.  They fix a bug introduced in v4.7-rc1
and so need to go into 4.7 and 4.8 stable trees.

-- 
Cheers,
Stephen Rothwell