anchor.diff:               (:area :wired))
     ;; When NIL, the lock is free, otherwise is set to
     ;; the thread that holds the lock.
  -  (owner nil) ; must be slot 5, after wait-queue is included.
  +  (owner nil)
     (stack-next nil))
   
   (defun acquire-mutex (mutex &optional (wait-p t))
  
positive.code:       (unless (not *pseudo-atomic*)
          (panic "Trying to acquire mutex " mutex " while pseudo-atomic.")))
      ;; Fast path - try to lock.
      (when (sys.int::%cas-struct-slot mutex 5 nil self)
        ;; We got it.
        (setf (mutex-stack-next mutex) (thread-mutex-stack self)
              (thread-mutex-stack self) mutex)
  
negative.code:   ;; Slow path.
    (lock-wait-queue mutex)
    ;; Try to acquire again, release may have been running.
    (when (eql (sys.int::cas (mutex-owner mutex) nil self) nil)
      ;; We got it.
      (setf (mutex-stack-next mutex) (thread-mutex-stack self)
            (thread-mutex-stack self) mutex)
  