selftests: team: Add a reference count leak test

Add a test for the issue that was fixed in "team: avoid NETDEV_CHANGEMTU
event when unregistering slave".

The test hangs due to a reference count leak without the fix:

 # make -C tools/testing/selftests TARGETS="drivers/net/team" TEST_PROGS=refleak.sh TEST_GEN_PROGS="" run_tests
 [...]
 TAP version 13
 1..1
 # timeout set to 45
 # selftests: drivers/net/team: refleak.sh
 [   50.681299][  T496] unregister_netdevice: waiting for dummy1 to become free. Usage count = 3
 [   71.185325][  T496] unregister_netdevice: waiting for dummy1 to become free. Usage count = 3

And passes with the fix:

 # make -C tools/testing/selftests TARGETS="drivers/net/team" TEST_PROGS=refleak.sh TEST_GEN_PROGS="" run_tests
 [...]
 TAP version 13
 1..1
 # timeout set to 45
 # selftests: drivers/net/team: refleak.sh
 ok 1 selftests: drivers/net/team: refleak.sh

Signed-off-by: Ido Schimmel <[email protected]>
Reviewed-by: Jiri Pirko <[email protected]>
Acked-by: Stanislav Fomichev <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: idosch

tools/testing/selftests/drivers/net/team/Makefile

@@ -5,6 +5,7 @@ TEST_PROGS := \
 	dev_addr_lists.sh \
 	options.sh \
 	propagation.sh \
+	refleak.sh \
 # end of TEST_PROGS
 
 TEST_INCLUDES := \

tools/testing/selftests/drivers/net/team/refleak.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# shellcheck disable=SC2154
+
+lib_dir=$(dirname "$0")
+source "$lib_dir"/../../../net/lib.sh
+
+trap cleanup_all_ns EXIT
+
+# Test that there is no reference count leak and that dummy1 can be deleted.
+# https://lore.kernel.org/netdev/[email protected]/
+setup_ns ns1 ns2
+ip -n "$ns1" link add name team1 type team
+ip -n "$ns1" link add name dummy1 mtu 1499 type dummy
+ip -n "$ns1" link set dev dummy1 master team1
+ip -n "$ns1" link set dev dummy1 netns "$ns2"
+ip -n "$ns2" link del dev dummy1