Debugging a backend stuck consuming CPU

Hi PostgreSQL community,

I am investigating a problem with a backend that appears to be stuck
and spinning while performing a "DISCARD ALL" command. The system is
running an older release 9.2.2. Are there any bugs that could be
causing this behavior? How can I tell what the process is actually
doing? It does not respond to either pg_cancel_backend() or to
pg_terminate_backend() so it is acting like it is not receiving the
signals. Any ideas on how to debug this would be appriciated.

Regards,
Ken