his information might be relevant.

We are able to reproduce the problem with unregister_netdevice: waiting
for lo to become free. Usage count = 1 with 4.14.0-rc3 kernel with
CONFIG_PREEMPT_NONE=y and running only on one CPU with following boot
kernel options:

BOOT_IMAGE=/boot/vmlinuz-4.14.0-rc3 root=/dev/mapper/vg0-root ro quiet 
vsyscall=emulate nosmp
Once we hit this state, it stays in this state and reboot is needed. No more 
containers can be spawned. We reproduce it by running images doing 
ipsec/openvpn connections + downloading a small file inside the tunnels. Then 
the instances exist (usually they run < 10s). We run 10s of such containers a 
minute on one machine. With the abovementioned settings (only 1cpu), the 
machine hits it in ~2 hours.

Another reproducer with the same kernel, but without limiting number of
CPUs, is to jus run iperf in UDP mode for 3 seconds inside the container
(so there is no TCP communication at all). If we run 10 of such
containers in parallel, wait for all of them to finish and do it again,
we hit the trouble in less than 10 minutes (on 40 cores machine).

In both of our reproducers, we added "ip route flush table all; ifconfig
down; sleep 10" before existing from containers. It does not seem to
have any effect.

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https://bugs.launchpad.net/bugs/1711407

Title:
  unregister_netdevice: waiting for lo to become free

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