Comment 7 for bug 212485

I experience this every ~5th shutdown, however the stack trace I see is:

rpcb_getport_async
rpc_malloc
call_bind
call_reserve
__rpc_execute
...

which corresponds to rpcb_clnt.c:322:
        BUG_ON(clnt->cl_parent != clnt);

This is called from a kernel thread context and I only see the bug_on trigger when shutting down, where NetworkManager cutts the ethernet connection before NFS is unmounted (yikes).