Re: [PATCH net-next v3 0/5] net: resegment oversized TCP GSO skbs

On Mon, 28 Sep 2026 19:34:21 -0400 Willem de Bruijn wrote:

If 1/5 fixes a bug that is reachable today (does it?) then it needs to
go to net on its own.

Before this series, it is reachable when the tag is already in the frame,
for example a stacked VLAN device or an OVS QinQ path.  I reproduced it
with the following script:

  ip netns add g1; ip netns add g2
  ip link add v0 type veth peer name v1
  ip link set v0 netns g1; ip link set v1 netns g2
  for n in g1 g2; do
      r=v0; [ $n = g2 ] && r=v1
      ip -n $n link add link $r name vlan200 type vlan id 200
      ip -n $n link add link vlan200 name vlan100 type vlan id 100
      for d in $r vlan200 vlan100; do
          ip -n $n link set $d gso_max_size 524280
      done
      ip -n $n link set $r up; ip -n $n link set vlan200 up
      ip -n $n link set vlan100 up
  done
  ip -n g1 addr add 2001:db8::1/64 dev vlan100
  ip -n g2 addr add 2001:db8::2/64 dev vlan100
  ip netns exec g2 iperf3 -s -D
  ip -n g1 link set v0 gso_ipv4_max_size 65536
  ip netns exec g1 iperf3 -c 2001:db8::2 -t 6
  ip -n g1 link set v0 gso_ipv4_max_size 524280
  ip netns exec g1 iperf3 -c 2001:db8::2 -t 6

With gso_ipv4_max_size = 65536, iperf3 reports 442 Mbps; with 524280, it
reports 39.4 Gbps.  So gso_ipv4_max_size clearly affects this IPv6 flow.

I will keep 1/5 in the series and drop the Fixes tag, as Paolo suggests.