Subject: Re: [PATCH net 2/2] selftest: net: add a test-case for encap segmentation after GRO

From: Willem de Bruijn <[email-masked]>
Date: Sun, 01 Feb 2026 17:19:11 -0500

Paolo Abeni wrote:
> We had a few patches in this area and no explicit coverage so far.
> The test case covers the scenario addressed by the previous fix;
> reusing the existing udpgro_fwd.sh script to leverage part of the
> of the virtual network setup, even if such script is possibly not
> a perfect fit.
> 
> Note that the mentioned script already contains several shellcheck
> violation; this patch does not fix the existing code, just avoids
> adding more issues in the new one.
> 
> Signed-off-by: Paolo Abeni <[email-masked]>

Reviewed-by: Willem de Bruijn <[email-masked]>

> ---
>  tools/testing/selftests/net/udpgro_fwd.sh | 65 +++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
> 
> diff --git a/tools/testing/selftests/net/udpgro_fwd.sh b/tools/testing/selftests/net/udpgro_fwd.sh
> index a39fdc4aa2ff..f2c1f0630b77 100755
> --- a/tools/testing/selftests/net/udpgro_fwd.sh
> +++ b/tools/testing/selftests/net/udpgro_fwd.sh
> @@ -162,6 +162,39 @@ run_test() {
>  	echo " ok"
>  }
>  
> +run_test_csum() {
> +	local -r msg="$1"
> +	local -r dst="$2"
> +	local csum_error_filter=UdpInCsumErrors
> +	local csum_errors
> +
> +	printf "%-40s" "$msg"
> +
> +	is_ipv6 "$dst" && csum_error_filter=Udp6InCsumErrors
> +
> +	ip netns exec "$NS_DST" iperf3 -s -1 >/dev/null &
> +	wait_local_port_listen "$NS_DST" 5201 tcp
> +	local spid="$!"
> +	ip netns exec "$NS_SRC" iperf3 -c "$dst" -t 2 >/dev/null
> +	local retc="$?"
> +	wait "$spid"
> +	local rets="$?"
> +	if [ "$rets" -ne 0 ] || [ "$retc" -ne 0 ]; then
> +		echo " fail client exit code $retc, server $rets"
> +		ret=1
> +		return
> +	fi
> +
> +	csum_errors=$(ip netns exec "$NS_DST" nstat -as "$csum_error_filter" |
> +		      grep "$csum_error_filter" | awk '{print $2}')
> +	if [ -n "$csum_errors" ] && [ "$csum_errors" -gt 0 ]; then
> +		echo " fail - csum error on receive $csum_errors, expected 0"
> +		ret=1
> +		return
> +	fi
> +	echo " ok"
> +}
> +
>  run_bench() {
>  	local -r msg=$1
>  	local -r dst=$2
> @@ -260,6 +293,38 @@ for family in 4 6; do
>  	ip netns exec $NS_SRC $PING -q -c 1 $OL_NET$DST_NAT >/dev/null
>  	run_test "GRO fwd over UDP tunnel" $OL_NET$DST_NAT 10 10 $OL_NET$DST
>  	cleanup
> +
> +	# force segmentation and re-aggregation
> +	create_vxlan_pair
> +	ip netns exec "$NS_DST" ethtool -K veth"$DST" generic-receive-offload on
> +	ip netns exec "$NS_SRC" ethtool -K veth"$SRC" tso off
> +	ip -n "$NS_SRC" link set dev veth"$SRC" mtu 1430
> +
> +	# forward to a 2nd veth pair
> +	ip -n "$NS_DST" link add br0 type bridge
> +	ip -n "$NS_DST" link set dev veth"$DST" master br0
> +
> +	# segment the aggregates TSO packet, without csum offload
> +	ip -n "$NS_DST" link add veth_segment type veth peer veth_rx
> +	for FEATURE in tso tx-udp-segmentation tx-checksumming; do
> +		ip netns exec "$NS_DST" ethtool -K veth_segment "$FEATURE" off
> +	done

fwiw, tx off will disable all the dependent tx offloads too

> +	ip -n "$NS_DST" link set dev veth_segment master br0 up
> +	ip -n "$NS_DST" link set dev br0 up
> +	ip -n "$NS_DST" link set dev veth_rx up
> +
> +	# move the lower layer IP in the last added veth
> +	for ADDR in "$BM_NET_V4$DST/24" "$BM_NET_V6$DST/64"; do
> +		# the dad argument will let iproute emit a unharmfull warning

unimportant but minor typo: unharmful. Also above aggregates -> aggregated

> +		# with ipv4 addresses
> +		ip -n "$NS_DST" addr del dev veth"$DST" "$ADDR" \
> +			nodad 2>/dev/null

nodad probably only matters on add?

> +		ip -n "$NS_DST" addr add dev veth_rx "$ADDR" \
> +			nodad 2>/dev/null
> +	done
> +
> +	run_test_csum "GSO after GRO" "$OL_NET$DST"
> +	cleanup
>  done
>  
>  exit $ret
> -- 
> 2.52.0
>