Dumping information about locks in use by sending a SIGHUP signal
to the server or by invoking the "mysqladmin debug" command may
lead to a server crash in debug builds or to undefined behavior in
production builds.

The problem was that a mutex that protects a lock object (THR_LOCK)
might have been destroyed before the lock object was actually removed
from the list of locks in use, causing a race condition with other
threads iterating over the list. The solution is to destroy the mutex
only after removing lock object from the list.