unregister_netdevice: waiting for lo to become free. Usage count = 2
leaked reference.
 netdev_tracker_alloc include/linux/netdevice.h:3860 [inline]
 dev_hold_track include/linux/netdevice.h:3877 [inline]
 ipv6_add_dev+0x3d8/0x10c0 net/ipv6/addrconf.c:408
 addrconf_notify+0x6a6/0x2110 net/ipv6/addrconf.c:3523
 notifier_call_chain kernel/notifier.c:84 [inline]
 raw_notifier_call_chain+0xe7/0x170 kernel/notifier.c:392
 call_netdevice_notifiers_info net/core/dev.c:1919 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:1931 [inline]
 call_netdevice_notifiers net/core/dev.c:1945 [inline]
 register_netdevice+0x15fd/0x1c00 net/core/dev.c:9698
 register_netdev+0x37/0x50 net/core/dev.c:9791
 loopback_net_init+0x6c/0x140 drivers/net/loopback.c:217
 ops_init+0x313/0x430 net/core/net_namespace.c:140
 setup_net+0x45b/0xb70 net/core/net_namespace.c:330
 copy_net_ns+0x359/0x5c0 net/core/net_namespace.c:474
 create_new_namespaces+0x4ce/0xa00 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0x11e/0x180 kernel/nsproxy.c:226
 ksys_unshare+0x57d/0xb50 kernel/fork.c:3058
 __do_sys_unshare kernel/fork.c:3129 [inline]
 __se_sys_unshare kernel/fork.c:3127 [inline]
 __x64_sys_unshare+0x34/0x40 kernel/fork.c:3127
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae