rb_first
for (rb = rb_first(&b->waiters); rb != NULL; rb = rb_next(rb))
for (rb = rb_first(&b->waiters); rb; rb = rb_next(rb)) {
GEM_BUG_ON(rb_first(&b->waiters) != &b->irq_wait->node);
GEM_BUG_ON(rb_first(&b->waiters) == &wait->node);
GEM_BUG_ON(rb_first(&b->waiters) !=
for (rb = rb_first(&b->waiters); rb; rb = rb_next(rb)) {