the MAC policy list is busy during a load or unload attempt.
We assert no locks held during the cv wait, meaning we should
be fairly deadlock-safe. Because of the cv model and busy
count, it's possible for a cv waiter waiting for exclusive
access to the policy list to be starved by active and
long-lived access control/labeling events. For now, we
accept that as a necessary tradeoff.
Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories