int dio_clu_sync(struct dio_cluster *cluster)
{
	int err;
	struct dio_io *io;

	if (!test_bit(DIO_CLU_DIRTY, &cluster->flags))
		return 0;

	down_write(&cluster->sync_rw_lock);
	if (!test_bit(DIO_CLU_DIRTY, &cluster->flags)) {
		err = 0;
		goto out;
	}

	io = dio_io_alloc(cluster);
	if (!io) {
		err = -ENOMEM;
		goto out;
	}

	set_bit(DIO_IO_WAIT, &io->flags);
	dio_submit(WRITE, io);
	wait_for_completion(&io->comp);
	trace_dio_clu_sync(cluster->index); /* tsk */
	err = io->err;
	if (!err)
		clear_bit(DIO_CLU_DIRTY, &cluster->flags);

	dio_io_deref(io);
out:
	up_write(&cluster->sync_rw_lock);

	return err;
}