Hi Dan,

so here are the information for the latest kernel (4.13.0-38.43+hf1711407v20180413b1):


The bug got reproduced:

[ 1085.626663] unregister_netdevice: possible namespace leak (netns ffff8d2dc3d34800), have been waiting for 60 seconds
[ 1085.626696]  (netns ffff8d2dc3d34800): dst ffff8d2dd006db00 expires 0 error 0 obsolete 2 flags 0 refcnt 1 ops ipv4_dst_ops+0x0/0xc0 creator ip_route_output_key_hash_rcu+0x355/0x9c0

If I grep the netns: ffff8d2dc3d34800, it is visible that during first 10 minutes, it outputs more info, then until ~ 1 hour, it says the same message more frequently and then only outputs it ever hour.

[  901.854919] net_namespace: alloced net ffff8d2dc3d34800
[ 1085.626663] unregister_netdevice: possible namespace leak (netns ffff8d2dc3d34800), have been waiting for 60 seconds
[ 1085.626696] 	(netns ffff8d2dc3d34800): dst ffff8d2dd006db00 expires 0 error 0 obsolete 2 flags 0 refcnt 1 ops ipv4_dst_ops+0x0/0xc0 creator ip_route_output_key_hash_rcu+0x355/0x9c0
[ 1095.706659] unregister_netdevice: possible namespace leak (netns ffff8d2dc3d34800), have been waiting for 70 seconds
[ 1095.706692] 	(netns ffff8d2dc3d34800): dst ffff8d2dd006db00 expires 0 error 0 obsolete 2 flags 0 refcnt 1 ops ipv4_dst_ops+0x0/0xc0 creator ip_route_output_key_hash_rcu+0x355/0x9c0
[ 1105.786651] unregister_netdevice: possible namespace leak (netns ffff8d2dc3d34800), have been waiting for 80 seconds
[ 1105.786669] 	(netns ffff8d2dc3d34800): dst ffff8d2dd006db00 expires 0 error 0 obsolete 2 flags 0 refcnt 1 ops ipv4_dst_ops+0x0/0xc0 creator ip_route_output_key_hash_rcu+0x355/0x9c0
[ 1115.866654] unregister_netdevice: possible namespace leak (netns ffff8d2dc3d34800), have been waiting for 90 seconds
....
[ 1631.003906] unregister_netdevice: likely namespace leak (netns ffff8d2dc3d34800), have been waiting for 605 seconds
[ 1641.147950] unregister_netdevice: likely namespace leak (netns ffff8d2dc3d34800), have been waiting for 616 seconds
[ 1651.291981] unregister_netdevice: likely namespace leak (netns ffff8d2dc3d34800), have been waiting for 626 seconds
[ 1661.372025] unregister_netdevice: likely namespace leak (netns ffff8d2dc3d34800), have been waiting for 636 seconds
[ 1671.452071] unregister_netdevice: likely namespace leak (netns ffff8d2dc3d34800), have been waiting for 646 seconds
[ 1681.564110] unregister_netdevice: likely namespace leak (netns ffff8d2dc3d34800), have been waiting for 656 seconds
...

[ 4628.301622] unregister_netdevice: namespace leak (netns ffff8d2dc3d34800), have been waiting for 3603 seconds
[ 8252.383668] unregister_netdevice: namespace leak (netns ffff8d2dc3d34800), have been waiting for 7227 seconds
[11877.333159] unregister_netdevice: namespace leak (netns ffff8d2dc3d34800), have been waiting for 10852 seconds
[15502.281254] unregister_netdevice: namespace leak (netns ffff8d2dc3d34800), have been waiting for 14477 seconds
[19127.230600] unregister_netdevice: namespace leak (netns ffff8d2dc3d34800), have been waiting for 18102 seconds
[22752.179625] unregister_netdevice: namespace leak (netns ffff8d2dc3d34800), have been waiting for 21727 seconds
[26377.129256] unregister_netdevice: namespace leak (netns ffff8d2dc3d34800), have been waiting for 25352 seconds
[30002.078342] unregister_netdevice: namespace leak (netns ffff8d2dc3d34800), have been waiting for 28977 seconds

The machine continue to run and the docker is still able to create new instances, i.e. there is no complete lock out. 

The machine continued to run further, and after an ~hour , 3 namespaces leaked. The machine now has load "3", which seems to be an artifact of this. Other than that, it seems to continue to run!