+ /*
+ * test_and_clear_bit(IPATH_PORT_WAITING_RCV) and
+ * test_and_clear_bit(IPATH_PORT_WAITING_URG) below
+ * would both like timely updates of the bits so that
+ * we don't pass them by unnecessarily. the rmb()
+ * here ensures that we see them promptly -- the
+ * corresponding wmb()'s are in ipath_poll_urgent()
+ * and ipath_poll_next()...
+ */