Update sema_up to properly yield during execution of an interrupt handler

src/threads/synch.c

@@ -120,6 +120,9 @@ sema_up (struct semaphore *sema)
   sema->value++;
   intr_set_level (old_level);
 
+  if (intr_context ())
+    intr_yield_on_return ();
+  else
     thread_yield ();
 }