On Mon, Mar 28, 2016 at 4:58 PM, Alexander Duyck [off-list ref] wrote:

This patch should fix the issues seen with a recent fix to prevent
tunnel-in-tunnel frames from being generated with GRO.  The fix itself is
correct for now as long as we do not add any devices that support
NETIF_F_GSO_GRE_CSUM.  When such a device is added it could have the
potential to mess things up due to the fact that the outer transport header
points to the outer UDP header and not the GRE header as would be expected.

Fixes: fac8e0f579695 ("tunnels: Don't apply GRO to multiple layers of encapsulation.")
Signed-off-by: Alexander Duyck <redacted>
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This should allow us to keep the fix that Jesse added without breaking the
3 cases that Tom called out in terms of FOU/GUE.

Additional work will be needed in net-next as we probably need to make it
so that offloads work correctly when we get around to supporting
NETIF_F_GSO_GRE_CSUM.

Thanks, this looks like a reasonable fix to me. I agree that there is
more that can be done in the future to improve things but this should
restore GRO while still avoiding possible issues.