x = pa[k - 1]; y = x->trb_link[0]; x->trb_link[0] = y->trb_link[1]; y->trb_link[1] = x; pa[k - 2]->trb_link[1] = y; if (y->trb_tag[1] == TRB_THREAD) { y->trb_tag[1] = TRB_CHILD; x->trb_tag[0] = TRB_THREAD; x->trb_link[0] = y; }