REQ_F_SINGLE_POLL
if (!(req->flags & (REQ_F_SINGLE_POLL | REQ_F_DOUBLE_POLL)))
if (req->flags & REQ_F_SINGLE_POLL)
req->flags &= ~REQ_F_SINGLE_POLL;
req->flags |= REQ_F_SINGLE_POLL;
req->flags &= ~(REQ_F_SINGLE_POLL | REQ_F_DOUBLE_POLL);