PDF_CLOSED
KASSERT((pd->pd_flags & PDF_CLOSED) == 0,
KASSERT((pd->pd_flags & PDF_CLOSED),
KASSERT((pd->pd_flags & PDF_CLOSED) == 0 || p->p_pptr == p->p_reaper,
if (pd->pd_flags & PDF_CLOSED) {
pd->pd_flags |= PDF_CLOSED;