src/threads/synch.c

@@ -265,6 +265,18 @@ lock_release (struct lock *lock)
   ASSERT (lock != NULL);
   ASSERT (lock_held_by_current_thread (lock));
 
+  struct thread *current_thread = thread_current ();
+  struct list_elem *tail = list_tail (&current_thread->donors_list);
+  for (struct list_elem *e = list_begin (&current_thread->donors_list);
+       e != tail; e = e->next)
+    {
+      struct thread *donor = list_entry (e, struct thread, donor_elem);
+      if (donor->waiting_lock == lock)
+        list_remove (e);
+    }
+
+  thread_recalculate_priority ();
+
   lock->holder = NULL;
   sema_up (&lock->semaphore);
 }

src/threads/thread.c

@@ -408,6 +408,13 @@ thread_get_priority (void)
   return thread_current ()->priority;
 }
 
+/* Recalculates the effective priority of the current thread. */
+void
+thread_recalculate_priority (void)
+{
+  barrier ();
+};
+
 /* Sets the current thread's nice value to NICE. */
 void
 thread_set_nice (int nice UNUSED) 

src/threads/thread.h

@@ -144,6 +144,7 @@ bool priority_more (const struct list_elem *a_, const struct list_elem *b_,
                     void *aux UNUSED);
 int thread_get_priority (void);
 void thread_set_priority (int);
+void thread_recalculate_priority (void);
 
 int thread_get_nice (void);
 void thread_set_nice (int);