Thread deadlock

Two threads will be stuck waiting forever if each holds a lock the other needs to acquire. Threads may try to acquire two locks in different orders, potentially causing deadlock
/src/mongo/db/repl/topology_version_observer.cpp:99: ORDER_REVERSAL 175260 "lk" and "this->this->_mutex" point to the same lock. [Note: The source code implementation of the function has been overridden by a builtin model.]