Comment 0 for bug 1919277

Issue found with 5.6.0-1048-oem

While debugging bug 1880631, I found that this test will cause dmesg flooded with:
"unregister_netdevice: waiting for eth0 to become free. Usage count = 1"
for about every 10 secondes.

Test log:
$ sudo ./l2tp.sh
TEST: IPv4 basic L2TP tunnel [ OK ]
TEST: IPv4 route through L2TP tunnel [ OK ]
TEST: IPv6 basic L2TP tunnel [ OK ]
TEST: IPv6 route through L2TP tunnel [ OK ]
TEST: IPv4 basic L2TP tunnel - with IPsec [ OK ]
TEST: IPv4 route through L2TP tunnel - with IPsec [ OK ]
TEST: IPv6 basic L2TP tunnel - with IPsec [ OK ]
TEST: IPv6 route through L2TP tunnel - with IPsec [ OK ]
TEST: IPv4 basic L2TP tunnel [ OK ]
TEST: IPv4 route through L2TP tunnel [ OK ]
TEST: IPv6 basic L2TP tunnel - with IPsec [ OK ]
TEST: IPv6 route through L2TP tunnel - with IPsec [ OK ]
TEST: IPv4 basic L2TP tunnel - after IPsec teardown [ OK ]
TEST: IPv4 route through L2TP tunnel - after IPsec teardown [ OK ]
TEST: IPv6 basic L2TP tunnel - after IPsec teardown [ OK ]
TEST: IPv6 route through L2TP tunnel - after IPsec teardown [ OK ]

Tests passed: 16
Tests failed: 0

dmesg output:
$ dmesg
Message from syslogd@glameow at Mar 16 05:01:40 ...
 kernel:[ 739.608359] unregister_netdevice: waiting for eth0 to become free. Usage count = 1
[ 708.560589] eth1: renamed from tmp
[ 708.587396] IPv6: ADDRCONF(NETDEV_CHANGE): eth1: link becomes ready
[ 708.587472] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[ 708.616950] eth2: renamed from tmp
[ 708.643341] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[ 708.687057] l2tp_core: L2TP core driver, V2.0
[ 708.689380] l2tp_netlink: L2TP netlink interface
[ 708.695479] l2tp_ip: L2TP IP encapsulation support (L2TPv3)
[ 708.700061] l2tp_eth: L2TP ethernet pseudowire support (L2TPv3)
[ 708.726295] l2tp_ip6: L2TP IP encapsulation support for IPv6 (L2TPv3)
[ 708.788973] Initializing XFRM netlink socket
[ 719.448364] unregister_netdevice: waiting for eth0 to become free. Usage count = 1
[ 729.528359] unregister_netdevice: waiting for eth0 to become free. Usage count = 1
[ 739.608359] unregister_netdevice: waiting for eth0 to become free. Usage count = 1

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.6.0-1048-oem 5.6.0-1048.52
ProcVersionSignature: User Name 5.6.0-1048.52-oem 5.6.19
Uname: Linux 5.6.0-1048-oem x86_64
ApportVersion: 2.20.11-0ubuntu27.16
Architecture: amd64
CasperMD5CheckResult: skip
Date: Tue Mar 16 05:20:45 2021
SourcePackage: linux-signed-oem-5.6
UpgradeStatus: No upgrade log present (probably fresh install)