REQ_DM_POLL_LIST
if (!(bio->bi_opf & REQ_DM_POLL_LIST)) {
bio->bi_opf |= REQ_DM_POLL_LIST;
if (!(bio->bi_opf & REQ_DM_POLL_LIST))
bio->bi_opf &= ~REQ_DM_POLL_LIST;
bio->bi_opf |= REQ_DM_POLL_LIST;
clone->bi_opf &= ~REQ_DM_POLL_LIST;