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

src/threads/thread.c

@@ -439,6 +439,12 @@ thread_get_recent_cpu (void)
   return 0;
 }
 
+void
+ready_list_reorder (void)
+{
+  list_sort (&ready_list, priority_more, NULL);
+}
+
 /* Idle thread.  Executes when no other thread is ready to run.
 
    The idle thread is initially put on the ready list by

src/threads/thread.h

@@ -150,6 +150,8 @@ void thread_set_nice (int);
 int thread_get_recent_cpu (void);
 int thread_get_load_avg (void);
 
+void ready_list_reorder (void);
+
 /* Returns true iff the priority of the first list element's thread is greater
    than that of the second list element's thread. */
 list_less_func thread_priority_greater;