TU_FLAG_NACK
if (test_bit(TU_FLAG_IN_PROCESS | TU_FLAG_NACK, &tu->flags)) {
clear_bit(TU_FLAG_NACK, &tu->flags);
set_bit(TU_FLAG_NACK, &tu->flags);
if (test_bit(TU_FLAG_IN_PROCESS | TU_FLAG_NACK, &tu->flags)) {