Implement priority donation helper function with propagation, w/ T

src/threads/synch.c

@@ -188,7 +188,21 @@ lock_init (struct lock *lock)
 }
 
 static void
-donate_priority (struct thread *donor, struct thread *donee);
+donate_priority (struct thread *donor, struct thread *donee) {
+  while (donee != NULL)
+    {
+      if (donor->priority <= donee->priority)
+          break;
+
+      donee->priority = donor->priority;
+      if (donee->waiting_lock == NULL)
+        donee = NULL;
+      else
+        donee = donee->waiting_lock->holder;
+    }
+
+  ready_list_reorder ();
+}
 
 /* Acquires LOCK, sleeping until it becomes available if
    necessary.  The lock must not already be held by the current