Why does Instance reboot fail with 'Failed to terminate process with SIGKILL: Device or resource busy' ?

Issue

• Instance reboot fails with the following error :

 1e774a3e-746d-4153-83ea-a22443adb95c | grep fault
    | fault                                | {"message": "Failed to terminate process 108082 with SIGKILL: Device or resource busy", "code": 500, "details": "  File     
    ​\"/usr/lib/python2.7/site-packages/nova/compute/
\", line 290, in decorated_function 

• The instance qemu-kvm process goes to defunct state & instance remains in error state on dashboard .