On Tue, Oct 27, 2020 at 5:52 PM Alexander Ovechkin [off-list ref] wrote:

quoted

But it was moved on purpose to avoid setting the inner protocol to IPPROTO_MPLS. That needs to use skb->inner_protocol to further segment.

And why do we need to avoid setting the inner protocol to IPPROTO_MPLS? Currently skb->inner_protocol is used before call of ip6_tnl_xmit.
Can you please give example when this patch breaks MPLS segmentation?

mpls_gso_segment calls skb_mac_gso_segment on the inner packet. After
setting skb->protocol based on skb->inner_protocol.

perhaps mpls encap gso and udp tunnel gso simply cannot be enabled
together, because both use skb->inner_(ipproto|protocol) to demultiplex:

  18    163  net/ipv4/udp_offload.c <<skb_udp_tunnel_segment>>
             protocol = skb->inner_protocol;
  19     35  net/mpls/mpls_gso.c <<mpls_gso_segment>>
             skb->protocol = skb->inner_protocol;

   3    168  net/ipv4/udp_offload.c <<skb_udp_tunnel_segment>>
             ops = rcu_dereference(offloads[skb->inner_ipproto]);

Please don't top post, btw.

quoted

On 16 Oct 2020, at 20:55, Willem de Bruijn [off-list ref] wrote:

On Fri, Oct 16, 2020 at 7:14 AM Alexander Ovechkin [off-list ref] wrote:

quoted

ip6_tnl_encap assigns to proto transport protocol which
encapsulates inner packet, but we must pass to set_inner_ipproto
protocol of that inner packet.

Calling set_inner_ipproto after ip6_tnl_encap might break gso.
For example, in case of encapsulating ipv6 packet in fou6 packet, inner_ipproto
would be set to IPPROTO_UDP instead of IPPROTO_IPV6. This would lead to
incorrect calling sequence of gso functions:
ipv6_gso_segment -> udp6_ufo_fragment -> skb_udp_tunnel_segment -> udp6_ufo_fragment
instead of:
ipv6_gso_segment -> udp6_ufo_fragment -> skb_udp_tunnel_segment -> ip6ip6_gso_segment

Signed-off-by: Alexander Ovechkin <redacted>

Commit 6c11fbf97e69 ("ip6_tunnel: add MPLS transmit support") moved
the call from ip6_tnl_encap's caller to inside ip6_tnl_encap.

It makes sense that that likely broke this behavior for UDP (L4) tunnels.

But it was moved on purpose to avoid setting the inner protocol to
IPPROTO_MPLS. That needs to use skb->inner_protocol to further
segment.

I suspect we need to set this before or after conditionally to avoid
breaking that use case.