not deleting threads when deleting a lock

kern/thread/synch.c

@@ -181,7 +181,6 @@ void lock_destroy(struct lock * lock)
   spinlock_cleanup(&(lock->spin));
   wchan_destroy(lock->wc);
   kfree(lock->lk_name);
-  kfree(lock->owner);
   kfree(lock);
 }