Comment 2 for bug 1657774

example of a nasty traceback in n-cpu that I suspect is related to this bug

http://logs.openstack.org/08/440308/1/check/gate-grenade-dsvm-ironic-inspector-ubuntu-xenial/7274f12/logs/old/screen-n-cpu.txt.gz?#_2017-03-02_11_16_32_358

and which actually fails a deletion of VM (in this case it was a instance on Ironic node).