[PATCH 06/14] tty/serial/core: Introduce poll_init callback

+	tport = &state->port;
+	if (!(tport->flags & ASYNC_INITIALIZED) && port->ops->poll_init) {
+		mutex_lock(&tport->mutex);
+		ret = port->ops->poll_init(port);
+		/*
+		 * We don't set ASYNCB_INITIALIZED as we only initialized the
+		 * hw, e.g. state->xmit is still uninitialized.
+		 */
+		mutex_unlock(&tport->mutex);
+		if (ret)
+			return ret;
+	}

What stops a parallel open or close changing ASYNC_INITIALIZED after you
test and before you lock ?

Alan