In src/mongo/db/db.h, line 39 in today's master branch seems misplaced:

            if( Lock::nested() ) {
                Lock::nested();
                massert(10298 , "can't temprelease nested lock", false);
            }

The second call to Lock::nested() doesn't do anything; it returns 'true' if the recursion count is greater than 1, but we already knew that from the line above and no one is looking at the result anyway.