Message-Id: <20240916191857.1082092-1-mitchell.augustin@canonical.com>
Date: Mon, 16 Sep 2024 14:18:57 -0500
From: mitchell.augustin@...onical.com
To: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	shuah@...nel.org,
	netdev@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: jacob.martin@...onical.com,
	dann.frazier@...onical.com,
	mitchell@...chellaugustin.com
Subject: [PATCH net-next] selftests: net: add pmtu_bad.sh regression test

From: Mitchell Augustin <mitchell.augustin@...onical.com>

Introduce a regression test that reproduces a bug in
pmtu_ipv6_ipv6_exception which causes veth_A-R1's reference
counter to remain > 0 after cleanup should have already
completed.

On affected kernels/platforms, running this test will result
in the following being displayed repeatedly in dmesg:
unregister_netdevice: waiting for veth_A-R1 to become free. Usage count = 5

and future attempts to modprobe/rmmod ip6_vti will hang forever.

Link: https://lore.kernel.org/all/CAHTA-uZDaJ-71o+bo8a96TV4ck-8niimztQFaa=QoeNdUm-9wg@mail.gmail.com/
Requested-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Mitchell Augustin <mitchell.augustin@...onical.com>
---
 tools/testing/selftests/net/pmtu_bad.sh | 901 ++++++++++++++++++++++++
 1 file changed, 901 insertions(+)
 create mode 100755 tools/testing/selftests/net/pmtu_bad.sh

diff --git a/tools/testing/selftests/net/pmtu_bad.sh b/tools/testing/selftests/net/pmtu_bad.sh
new file mode 100755
index 000000000000..4bbc9815b661
--- /dev/null
+++ b/tools/testing/selftests/net/pmtu_bad.sh
@@ -0,0 +1,901 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Pinned version of pmtu.sh pmtu_ipv6_ipv6_exception and all dependencies
+# configured to reproduce a kernel bug where the veth_A-R1 device's
+# resource counter remains > 0 after cleanup should have already been
+# completed.
+#
+# On affected kernels/platforms, running this test will result in the following
+# being displayed repeatedly in dmesg:
+# unregister_netdevice: waiting for veth_A-R1 to become free. Usage count = 5
+#
+# and future attempts to modprobe/rmmod ip6_vti will hang forever.
+#
+# Link: https://lore.kernel.org/all/CAHTA-uZDaJ-71o+bo8a96TV4ck-8niimztQFaa=QoeNdUm-9wg@mail.gmail.com/
+#
+# BugLink: https://bugs.launchpad.net/ubuntu-kernel-tests/+bug/2072501
+#
+# pmtu.sh:
+# Check that route PMTU values match expectations, and that initial device MTU
+# values are assigned correctly
+#
+# Tests currently implemented:
+#
+# - pmtu_bad
+# 	Sets the CPU governor to "performance" for all CPUs, then
+# 	runs a pinned, affected version of the pmtu_ipv6_ipv6_exception test with
+# 	nexthop objects 100 times. If this causes the following to be output
+# 	to dmesg, the test is considered to have failed and returns an error:
+#
+# 	unregister_netdevice: waiting for veth_A-R1 to become free
+#
+# 	Otherwise, the test passes. After execution of the test, the CPU governor
+# 	is restored to its original settings.
+# - pmtu_ipv6_ipv6_exception
+#	Same as pmtu_ipv4_vxlan4, but using a IPv4/IPv6 tunnel over IPv4/IPv6,
+#	instead of VXLAN
+
+# Pinned version of lib.sh
+##############################################################################
+# Defines
+
+WAIT_TIMEOUT=${WAIT_TIMEOUT:=20}
+BUSYWAIT_TIMEOUT=$((WAIT_TIMEOUT * 1000)) # ms
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+# namespace list created by setup_ns
+NS_LIST=()
+
+##############################################################################
+# Helpers
+
+__ksft_status_merge()
+{
+	local a=$1; shift
+	local b=$1; shift
+	local -A weights
+	local weight=0
+
+	local i
+	for i in "$@"; do
+		weights[$i]=$((weight++))
+	done
+
+	if [[ ${weights[$a]} > ${weights[$b]} ]]; then
+		echo "$a"
+		return 0
+	else
+		echo "$b"
+		return 1
+	fi
+}
+
+ksft_status_merge()
+{
+	local a=$1; shift
+	local b=$1; shift
+
+	__ksft_status_merge "$a" "$b" \
+		$ksft_pass $ksft_xfail $ksft_skip $ksft_fail
+}
+
+ksft_exit_status_merge()
+{
+	local a=$1; shift
+	local b=$1; shift
+
+	__ksft_status_merge "$a" "$b" \
+		$ksft_xfail $ksft_pass $ksft_skip $ksft_fail
+}
+
+loopy_wait()
+{
+	local sleep_cmd=$1; shift
+	local timeout_ms=$1; shift
+
+	local start_time="$(date -u +%s%3N)"
+	while true
+	do
+		local out
+		if out=$("$@"); then
+			echo -n "$out"
+			return 0
+		fi
+
+		local current_time="$(date -u +%s%3N)"
+		if ((current_time - start_time > timeout_ms)); then
+			echo -n "$out"
+			return 1
+		fi
+
+		$sleep_cmd
+	done
+}
+
+busywait()
+{
+	local timeout_ms=$1; shift
+
+	loopy_wait : "$timeout_ms" "$@"
+}
+
+# timeout in seconds
+slowwait()
+{
+	local timeout_sec=$1; shift
+
+	loopy_wait "sleep 0.1" "$((timeout_sec * 1000))" "$@"
+}
+
+until_counter_is()
+{
+	local expr=$1; shift
+	local current=$("$@")
+
+	echo $((current))
+	((current $expr))
+}
+
+busywait_for_counter()
+{
+	local timeout=$1; shift
+	local delta=$1; shift
+
+	local base=$("$@")
+	busywait "$timeout" until_counter_is ">= $((base + delta))" "$@"
+}
+
+slowwait_for_counter()
+{
+	local timeout=$1; shift
+	local delta=$1; shift
+
+	local base=$("$@")
+	slowwait "$timeout" until_counter_is ">= $((base + delta))" "$@"
+}
+
+cleanup_ns()
+{
+	local ns=""
+	local errexit=0
+	local ret=0
+
+	# disable errexit temporary
+	if [[ $- =~ "e" ]]; then
+		errexit=1
+		set +e
+	fi
+
+	for ns in "$@"; do
+		[ -z "${ns}" ] && continue
+		ip netns delete "${ns}" &> /dev/null
+		if ! busywait $BUSYWAIT_TIMEOUT ip netns list \| grep -vq "^$ns$" &> /dev/null; then
+			echo "Warn: Failed to remove namespace $ns"
+			ret=1
+		fi
+	done
+
+	[ $errexit -eq 1 ] && set -e
+	return $ret
+}
+
+cleanup_all_ns()
+{
+	cleanup_ns "${NS_LIST[@]}"
+}
+
+# setup netns with given names as prefix. e.g
+# setup_ns local remote
+setup_ns()
+{
+	local ns=""
+	local ns_name=""
+	local ns_list=()
+	local ns_exist=
+	for ns_name in "$@"; do
+		# Some test may setup/remove same netns multi times
+		if unset ${ns_name} 2> /dev/null; then
+			ns="${ns_name,,}-$(mktemp -u XXXXXX)"
+			eval readonly ${ns_name}="$ns"
+			ns_exist=false
+		else
+			eval ns='$'${ns_name}
+			cleanup_ns "$ns"
+			ns_exist=true
+		fi
+
+		if ! ip netns add "$ns"; then
+			echo "Failed to create namespace $ns_name"
+			cleanup_ns "${ns_list[@]}"
+			return $ksft_skip
+		fi
+		ip -n "$ns" link set lo up
+		! $ns_exist && ns_list+=("$ns")
+	done
+	NS_LIST+=("${ns_list[@]}")
+}
+
+tc_rule_stats_get()
+{
+	local dev=$1; shift
+	local pref=$1; shift
+	local dir=$1; shift
+	local selector=${1:-.packets}; shift
+
+	tc -j -s filter show dev $dev ${dir:-ingress} pref $pref \
+	    | jq ".[1].options.actions[].stats$selector"
+}
+
+tc_rule_handle_stats_get()
+{
+	local id=$1; shift
+	local handle=$1; shift
+	local selector=${1:-.packets}; shift
+	local netns=${1:-""}; shift
+
+	tc $netns -j -s filter show $id \
+	    | jq ".[] | select(.options.handle == $handle) | \
+		  .options.actions[0].stats$selector"
+}
+
+# Pinned version of net_helper.sh
+wait_local_port_listen()
+{
+	local listener_ns="${1}"
+	local port="${2}"
+	local protocol="${3}"
+	local pattern
+	local i
+
+	pattern=":$(printf "%04X" "${port}") "
+
+	# for tcp protocol additionally check the socket state
+	[ ${protocol} = "tcp" ] && pattern="${pattern}0A"
+	for i in $(seq 10); do
+		if ip netns exec "${listener_ns}" awk '{print $2" "$4}' \
+		   /proc/net/"${protocol}"* | grep -q "${pattern}"; then
+			break
+		fi
+		sleep 0.1
+	done
+}
+
+
+
+PAUSE_ON_FAIL=no
+VERBOSE=0
+TRACING=0
+
+# Some systems don't have a ping6 binary anymore
+which ping6 > /dev/null 2>&1 && ping6=$(which ping6) || ping6=$(which ping)
+
+#               Name                          Description                  re-run with nh
+tests="
+	pmtu_bad	Runs IPv6 over IPv6: PMTU exceptions 100x w/ performance governor		1"
+
+# Addressing and routing for tests with routers: four network segments, with
+# index SEGMENT between 1 and 4, a common prefix (PREFIX4 or PREFIX6) and an
+# identifier ID, which is 1 for hosts (A and B), 2 for routers (R1 and R2).
+# Addresses are:
+# - IPv4: PREFIX4.SEGMENT.ID (/24)
+# - IPv6: PREFIX6:SEGMENT::ID (/64)
+prefix4="10.0"
+prefix6="fc00"
+a_r1=1
+a_r2=2
+b_r1=3
+b_r2=4
+#	ns	peer	segment
+routing_addrs="
+	A	R1	${a_r1}
+	A	R2	${a_r2}
+	B	R1	${b_r1}
+	B	R2	${b_r2}
+"
+# Traffic from A to B goes through R1 by default, and through R2, if destined to
+# B's address on the b_r2 segment.
+# Traffic from B to A goes through R1.
+#	ns	destination		gateway
+routes="
+	A	default			${prefix4}.${a_r1}.2
+	A	${prefix4}.${b_r2}.1	${prefix4}.${a_r2}.2
+	B	default			${prefix4}.${b_r1}.2
+
+	A	default			${prefix6}:${a_r1}::2
+	A	${prefix6}:${b_r2}::1	${prefix6}:${a_r2}::2
+	B	default			${prefix6}:${b_r1}::2
+"
+USE_NH="no"
+#	ns	family	nh id	   destination		gateway
+nexthops="
+	A	4	41	${prefix4}.${a_r1}.2	veth_A-R1
+	A	4	42	${prefix4}.${a_r2}.2	veth_A-R2
+	B	4	41	${prefix4}.${b_r1}.2	veth_B-R1
+
+	A	6	61	${prefix6}:${a_r1}::2	veth_A-R1
+	A	6	62	${prefix6}:${a_r2}::2	veth_A-R2
+	B	6	61	${prefix6}:${b_r1}::2	veth_B-R1
+"
+
+# nexthop id correlates to id in nexthops config above
+#	ns    family	prefix			nh id
+routes_nh="
+	A	4	default			41
+	A	4	${prefix4}.${b_r2}.1	42
+	B	4	default			41
+
+	A	6	default			61
+	A	6	${prefix6}:${b_r2}::1	62
+	B	6	default			61
+"
+
+policy_mark=0x04
+rt_table=main
+
+veth4_a_addr="192.168.1.1"
+veth4_b_addr="192.168.1.2"
+veth4_c_addr="192.168.2.10"
+veth4_mask="24"
+veth6_a_addr="fd00:1::a"
+veth6_b_addr="fd00:1::b"
+veth6_c_addr="fd00:2::c"
+veth6_mask="64"
+
+tunnel4_a_addr="192.168.2.1"
+tunnel4_b_addr="192.168.2.2"
+tunnel4_mask="24"
+tunnel6_a_addr="fd00:2::a"
+tunnel6_b_addr="fd00:2::b"
+tunnel6_mask="64"
+
+dummy6_0_prefix="fc00:1000::"
+dummy6_1_prefix="fc00:1001::"
+dummy6_mask="64"
+
+err_buf=
+tcpdump_pids=
+nettest_pids=
+socat_pids=
+tmpoutfile=
+
+err() {
+	err_buf="${err_buf}${1}
+"
+}
+
+err_flush() {
+	echo -n "${err_buf}"
+	err_buf=
+}
+
+run_cmd() {
+	cmd="$*"
+
+	if [ "$VERBOSE" = "1" ]; then
+		printf "    COMMAND: $cmd\n"
+	fi
+
+	out="$($cmd 2>&1)"
+	rc=$?
+	if [ "$VERBOSE" = "1" -a -n "$out" ]; then
+		echo "    $out"
+		echo
+	fi
+
+	return $rc
+}
+
+run_cmd_bg() {
+	cmd="$*"
+
+	if [ "$VERBOSE" = "1" ]; then
+		printf "    COMMAND: %s &\n" "${cmd}"
+	fi
+
+	$cmd 2>&1 &
+}
+
+# Find the auto-generated name for this namespace
+nsname() {
+	eval echo \$NS_$1
+}
+
+setup_ipvX_over_ipvY() {
+	inner=${1}
+	outer=${2}
+
+	if [ "${outer}" -eq 4 ]; then
+		a_addr="${prefix4}.${a_r1}.1"
+		b_addr="${prefix4}.${b_r1}.1"
+		if [ "${inner}" -eq 4 ]; then
+			type="ipip"
+			mode="ipip"
+		else
+			type="sit"
+			mode="ip6ip"
+		fi
+	else
+		a_addr="${prefix6}:${a_r1}::1"
+		b_addr="${prefix6}:${b_r1}::1"
+		type="ip6tnl"
+		if [ "${inner}" -eq 4 ]; then
+			mode="ipip6"
+		else
+			mode="ip6ip6"
+		fi
+	fi
+
+	run_cmd ${ns_a} ip link add ip_a type ${type} local ${a_addr} remote ${b_addr} mode ${mode} || return $ksft_skip
+	run_cmd ${ns_b} ip link add ip_b type ${type} local ${b_addr} remote ${a_addr} mode ${mode}
+
+	run_cmd ${ns_a} ip link set ip_a up
+	run_cmd ${ns_b} ip link set ip_b up
+
+	if [ "${inner}" = "4" ]; then
+		run_cmd ${ns_a} ip addr add ${tunnel4_a_addr}/${tunnel4_mask} dev ip_a
+		run_cmd ${ns_b} ip addr add ${tunnel4_b_addr}/${tunnel4_mask} dev ip_b
+	else
+		run_cmd ${ns_a} ip addr add ${tunnel6_a_addr}/${tunnel6_mask} dev ip_a
+		run_cmd ${ns_b} ip addr add ${tunnel6_b_addr}/${tunnel6_mask} dev ip_b
+	fi
+}
+
+setup_ip6ip6() {
+	setup_ipvX_over_ipvY 6 6
+}
+
+setup_namespaces() {
+	setup_ns NS_A NS_B NS_C NS_R1 NS_R2
+	for n in ${NS_A} ${NS_B} ${NS_C} ${NS_R1} ${NS_R2}; do
+		# Disable DAD, so that we don't have to wait to use the
+		# configured IPv6 addresses
+		ip netns exec ${n} sysctl -q net/ipv6/conf/default/accept_dad=0
+	done
+	ns_a="ip netns exec ${NS_A}"
+	ns_b="ip netns exec ${NS_B}"
+	ns_c="ip netns exec ${NS_C}"
+	ns_r1="ip netns exec ${NS_R1}"
+	ns_r2="ip netns exec ${NS_R2}"
+}
+
+
+setup_routing_old() {
+	for i in ${routes}; do
+		[ "${ns}" = "" ]	&& ns="${i}"		&& continue
+		[ "${addr}" = "" ]	&& addr="${i}"		&& continue
+		[ "${gw}" = "" ]	&& gw="${i}"
+
+		ns_name="$(nsname ${ns})"
+
+		ip -n "${ns_name}" route add "${addr}" table "${rt_table}" via "${gw}"
+
+		ns=""; addr=""; gw=""
+	done
+}
+
+setup_routing_new() {
+	for i in ${nexthops}; do
+		[ "${ns}" = "" ]	&& ns="${i}"		&& continue
+		[ "${fam}" = "" ]	&& fam="${i}"		&& continue
+		[ "${nhid}" = "" ]	&& nhid="${i}"		&& continue
+		[ "${gw}" = "" ]	&& gw="${i}"		&& continue
+		[ "${dev}" = "" ]	&& dev="${i}"
+
+		ns_name="$(nsname ${ns})"
+
+		ip -n ${ns_name} -${fam} nexthop add id ${nhid} via ${gw} dev ${dev}
+
+		ns=""; fam=""; nhid=""; gw=""; dev=""
+
+	done
+
+	for i in ${routes_nh}; do
+		[ "${ns}" = "" ]	&& ns="${i}"		&& continue
+		[ "${fam}" = "" ]	&& fam="${i}"		&& continue
+		[ "${addr}" = "" ]	&& addr="${i}"		&& continue
+		[ "${nhid}" = "" ]	&& nhid="${i}"
+
+		ns_name="$(nsname ${ns})"
+
+		ip -n "${ns_name}" -"${fam}" route add "${addr}" table "${rt_table}" nhid "${nhid}"
+
+		ns=""; fam=""; addr=""; nhid=""
+	done
+}
+
+setup_routing() {
+	for i in ${NS_R1} ${NS_R2}; do
+		ip netns exec ${i} sysctl -q net/ipv4/ip_forward=1
+		ip netns exec ${i} sysctl -q net/ipv6/conf/all/forwarding=1
+	done
+
+	for i in ${routing_addrs}; do
+		[ "${ns}" = "" ]	&& ns="${i}"		&& continue
+		[ "${peer}" = "" ]	&& peer="${i}"		&& continue
+		[ "${segment}" = "" ]	&& segment="${i}"
+
+		ns_name="$(nsname ${ns})"
+		peer_name="$(nsname ${peer})"
+		if="veth_${ns}-${peer}"
+		ifpeer="veth_${peer}-${ns}"
+
+		# Create veth links
+		ip link add ${if} up netns ${ns_name} type veth peer name ${ifpeer} netns ${peer_name} || return 1
+		ip -n ${peer_name} link set dev ${ifpeer} up
+
+		# Add addresses
+		ip -n ${ns_name}   addr add ${prefix4}.${segment}.1/24  dev ${if}
+		ip -n ${ns_name}   addr add ${prefix6}:${segment}::1/64 dev ${if}
+
+		ip -n ${peer_name} addr add ${prefix4}.${segment}.2/24  dev ${ifpeer}
+		ip -n ${peer_name} addr add ${prefix6}:${segment}::2/64 dev ${ifpeer}
+
+		ns=""; peer=""; segment=""
+	done
+
+	if [ "$USE_NH" = "yes" ]; then
+		setup_routing_new
+	else
+		setup_routing_old
+	fi
+
+	return 0
+}
+
+
+setup() {
+	[ "$(id -u)" -ne 0 ] && echo "  need to run as root" && return $ksft_skip
+
+	for arg do
+		eval setup_${arg} || { echo "  ${arg} not supported"; return 1; }
+	done
+}
+
+trace() {
+	[ $TRACING -eq 0 ] && return
+
+	for arg do
+		[ "${ns_cmd}" = "" ] && ns_cmd="${arg}" && continue
+		${ns_cmd} tcpdump --immediate-mode -s 0 -i "${arg}" -w "${name}_${arg}.pcap" 2> /dev/null &
+		tcpdump_pids="${tcpdump_pids} $!"
+		ns_cmd=
+	done
+	sleep 1
+}
+
+
+restore_governors() {
+	echo "Restoring original CPU governors"
+	while IFS=' ' read -r cpu governor; do
+		echo "$governor" | tee "/sys/devices/system/cpu/$cpu/cpufreq/scaling_governor" > /dev/null
+	done < "$GOVERNOR_STATE_FILE"
+	rm -rf "$STATE_FILE_DIR" 2>/dev/null
+}
+
+
+cleanup() {
+	for pid in ${tcpdump_pids}; do
+		kill ${pid}
+	done
+	tcpdump_pids=
+
+	for pid in ${nettest_pids}; do
+		kill ${pid}
+	done
+	nettest_pids=
+
+	for pid in ${socat_pids}; do
+		kill "${pid}"
+	done
+	socat_pids=
+
+	cleanup_all_ns
+
+	ip link del veth_A-C			2>/dev/null
+	ip link del veth_A-R1			2>/dev/null
+	ovs-vsctl --if-exists del-port vxlan_a	2>/dev/null
+	ovs-vsctl --if-exists del-br ovs_br0	2>/dev/null
+	rm -f "$tmpoutfile"
+}
+
+mtu() {
+	ns_cmd="${1}"
+	dev="${2}"
+	mtu="${3}"
+
+	${ns_cmd} ip link set dev ${dev} mtu ${mtu}
+}
+
+mtu_parse() {
+	input="${1}"
+
+	next=0
+	for i in ${input}; do
+		[ ${next} -eq 1 -a "${i}" = "lock" ] && next=2 && continue
+		[ ${next} -eq 1 ] && echo "${i}" && return
+		[ ${next} -eq 2 ] && echo "lock ${i}" && return
+		[ "${i}" = "mtu" ] && next=1
+	done
+}
+
+link_get() {
+	ns_cmd="${1}"
+	name="${2}"
+
+	${ns_cmd} ip link show dev "${name}"
+}
+
+link_get_mtu() {
+	ns_cmd="${1}"
+	name="${2}"
+
+	mtu_parse "$(link_get "${ns_cmd}" ${name})"
+}
+
+route_get_dst_exception() {
+	ns_cmd="${1}"
+	dst="${2}"
+	dsfield="${3}"
+
+	if [ -z "${dsfield}" ]; then
+		dsfield=0
+	fi
+
+	${ns_cmd} ip route get "${dst}" dsfield "${dsfield}"
+}
+
+route_get_dst_pmtu_from_exception() {
+	ns_cmd="${1}"
+	dst="${2}"
+	dsfield="${3}"
+
+	mtu_parse "$(route_get_dst_exception "${ns_cmd}" "${dst}" "${dsfield}")"
+}
+
+check_pmtu_value() {
+	expected="${1}"
+	value="${2}"
+	event="${3}"
+
+	[ "${expected}" = "any" ] && [ -n "${value}" ] && return 0
+	[ "${value}" = "${expected}" ] && return 0
+	[ -z "${value}" ] &&    err "  PMTU exception wasn't created after ${event}" && return 1
+	[ -z "${expected}" ] && err "  PMTU exception shouldn't exist after ${event}" && return 1
+	err "  found PMTU exception with incorrect MTU ${value}, expected ${expected}, after ${event}"
+	return 1
+}
+
+
+test_pmtu_ipvX_over_ipvY_exception() {
+	inner=${1}
+	outer=${2}
+	ll_mtu=4000
+
+	setup namespaces routing ip${inner}ip${outer} || return $ksft_skip
+
+	trace "${ns_a}" ip_a         "${ns_b}"  ip_b  \
+	      "${ns_a}" veth_A-R1    "${ns_r1}" veth_R1-A \
+	      "${ns_b}" veth_B-R1    "${ns_r1}" veth_R1-B
+
+	if [ ${inner} -eq 4 ]; then
+		ping=ping
+		dst=${tunnel4_b_addr}
+	else
+		ping=${ping6}
+		dst=${tunnel6_b_addr}
+	fi
+
+	if [ ${outer} -eq 4 ]; then
+		#                      IPv4 header
+		exp_mtu=$((${ll_mtu} - 20))
+	else
+		#                      IPv6 header   Option 4
+		exp_mtu=$((${ll_mtu} - 40          - 8))
+	fi
+
+	# Create route exception by exceeding link layer MTU
+	mtu "${ns_a}"  veth_A-R1 $((${ll_mtu} + 1000))
+	mtu "${ns_r1}" veth_R1-A $((${ll_mtu} + 1000))
+	mtu "${ns_b}"  veth_B-R1 ${ll_mtu}
+	mtu "${ns_r1}" veth_R1-B ${ll_mtu}
+
+	mtu "${ns_a}" ip_a $((${ll_mtu} + 1000)) || return
+	mtu "${ns_b}" ip_b $((${ll_mtu} + 1000)) || return
+	run_cmd ${ns_a} ${ping} -q -M want -i 0.1 -w 1 -s $((${ll_mtu} + 500)) ${dst}
+
+	# Check that exception was created
+	pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${dst})"
+	check_pmtu_value ${exp_mtu} "${pmtu}" "exceeding link layer MTU on ip${inner}ip${outer} interface"
+}
+
+test_pmtu_ipv6_ipv6_exception() {
+	test_pmtu_ipvX_over_ipvY_exception 6 6
+}
+
+run_test() {
+	(
+	tname="$1"
+	tdesc="$2"
+
+	unset IFS
+
+	# Since cleanup() relies on variables modified by this subshell, it
+	# has to run in this context.
+	trap cleanup EXIT
+
+	if [ "$VERBOSE" = "1" ]; then
+		printf "\n##########################################################################\n\n"
+	fi
+
+	eval test_${tname}
+	ret=$?
+
+	if [ $ret -eq 0 ]; then
+		printf "TEST: %-60s  [ OK ]\n" "${tdesc}"
+	elif [ $ret -eq 1 ]; then
+		printf "TEST: %-60s  [FAIL]\n" "${tdesc}"
+		if [ "${PAUSE_ON_FAIL}" = "yes" ]; then
+			echo
+			echo "Pausing. Hit enter to continue"
+			read a
+		fi
+		err_flush
+		exit 1
+	elif [ $ret -eq $ksft_skip ]; then
+		printf "TEST: %-60s  [SKIP]\n" "${tdesc}"
+		err_flush
+	fi
+
+	return $ret
+	)
+	ret=$?
+	case $ret in
+		0)
+			all_skipped=false
+			[ $exitcode -eq $ksft_skip ] && exitcode=0
+		;;
+		$ksft_skip)
+			[ $all_skipped = true ] && exitcode=$ksft_skip
+		;;
+		*)
+			all_skipped=false
+			exitcode=1
+		;;
+	esac
+
+	return $ret
+}
+
+run_test_nh() {
+	tname="$1"
+	tdesc="$2"
+
+	USE_NH=yes
+	run_test "${tname}" "${tdesc} - nexthop objects"
+	USE_NH=no
+}
+
+usage() {
+	echo
+	echo "$0 [OPTIONS]..."
+	echo "Runs pmtu_ipv6_ipv6_exception test 100x"
+	echo
+	echo "Options"
+	echo "  --trace: capture traffic to TEST_INTERFACE.pcap"
+	echo
+	echo "Available tests${tests}"
+	exit 1
+}
+
+################################################################################
+#
+
+[ "$(id -u)" -ne 0 ] && echo "ERROR: need to run as root" && exit 1
+exitcode=0
+desc=0
+all_skipped=true
+
+while getopts :ptv o
+do
+	case $o in
+	p) PAUSE_ON_FAIL=yes;;
+	v) VERBOSE=1;;
+	t) if which tcpdump > /dev/null 2>&1; then
+		TRACING=1
+	   else
+		echo "=== tcpdump not available, tracing disabled"
+	   fi
+	   ;;
+	*) usage;;
+	esac
+done
+shift $(($OPTIND-1))
+
+IFS="
+"
+
+for arg do
+	# Check first that all requested tests are available before running any
+	command -v > /dev/null "test_${arg}" || { echo "=== Test ${arg} not found"; usage; }
+done
+
+trap cleanup EXIT
+
+# start clean
+cleanup
+
+HAVE_NH=no
+ip nexthop ls >/dev/null 2>&1
+[ $? -eq 0 ] && HAVE_NH=yes
+
+name=""
+desc=""
+rerun_nh=0
+
+# Set to performance governor so we can reproduce the bug
+STATE_FILE_DIR=$(mktemp -d)
+if [[ ! -d "$STATE_FILE_DIR" ]]; then
+	echo "Could not create temp dir, skipping this test" >&2
+	exit 1
+fi
+
+# Save current CPU governor state to temp file
+GOVERNOR_STATE_FILE="$STATE_FILE_DIR/orig_cpu_governors.txt"
+touch $GOVERNOR_STATE_FILE
+if [[ ! -e "$GOVERNOR_STATE_FILE" ]]; then
+	echo "Could not save current performance governor states, skipping this test" >&2
+	exit 1
+fi
+echo "Saving current performance governor settings"
+for cpu in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor; do
+	if [[ $cpu =~ ^/sys/devices/system/cpu/(cpu[0-9]+)/cpufreq/scaling_governor$ ]]; then
+		echo "${BASH_REMATCH[1]} $(cat $cpu)" >> "$GOVERNOR_STATE_FILE"
+	fi
+done
+
+# Restore original CPU governor settings
+trap restore_governors EXIT
+
+echo "Switching CPU governor to performance"
+for cpu in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor; do
+	if [[ $cpu =~ ^/sys/devices/system/cpu/(cpu[0-9]+)/cpufreq/scaling_governor$ ]]; then
+		echo "performance" | tee $cpu > /dev/null
+	fi
+done
+
+for i in $(seq 1 100);
+do
+	name="pmtu_ipv6_ipv6_exception"
+	desc="Bad PMTU behavior"
+
+	if [ "${HAVE_NH}" = "yes" ]; then
+		rerun_nh="${t}"
+	fi
+
+	run_this=1
+	for arg do
+		[ "${arg}" != "${arg#--*}" ] && continue
+		[ "${arg}" = "${name}" ] && run_this=1 && break
+		run_this=0
+	done
+	if [ $run_this -eq 1 ]; then
+		run_test_nh "${name}" "${desc}"
+	fi
+	name=""
+	desc=""
+	rerun_nh=0
+done
+
+if dmesg | grep -q "unregister_netdevice: waiting for veth_A-R1 to become free"; then
+	printf "TEST: Bad PMTU behavior - veth_A-R1 refcount error reproducer  [FAIL]\n"
+	printf "veth_A-R1 has not been released properly\n"
+	exitcode=1
+else
+	printf "TEST: Bad PMTU behavior - veth_A-R1 refcount error reproducer  [PASS]\n"
+	printf "No veth_A-R1 errors, considering this test passed\n"
+	exitcode=0
+fi
+
+exit ${exitcode}
-- 
2.43.0

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