TDF_BORROWING
td->td_flags |= TDF_BORROWING;
td->td_flags &= ~TDF_BORROWING;
if (td->td_flags & TDF_BORROWING && td->td_priority < prio)
td->td_flags |= TDF_BORROWING;
td->td_flags &= ~TDF_BORROWING;
if (td->td_flags & TDF_BORROWING && td->td_priority < prio)
KASSERT((td->td_flags & TDF_BORROWING) == 0,