+#define push_rcu(stack, p, len) ({                                             \
+		if (rcu_access_pointer(p)) {                                   \
+			BUG_ON(len >= 128);                                    \
+			stack[len++] = rcu_dereference_raw(p);                 \
+		}                                                              \
+		true;                                                          \
+	})
+static void root_free_rcu(struct rcu_head *rcu)
+{
+	struct allowedips_node *node, *stack[128] = {
+		container_of(rcu, struct allowedips_node, rcu) };
+	unsigned int len = 1;
+
+	while (len > 0 && (node = stack[--len]) &&
+	       push_rcu(stack, node->bit[0], len) &&
+	       push_rcu(stack, node->bit[1], len))
+		kfree(node);
+}

Hi Jason

I see this BUG_ON() is still here. It really needs to be removed. It
does not look like you need to crash the kernel here. Can you add in a
test of len >= 128, do a WARN and then return. I think you then leak
some memory, but i would much prefer that to a crashed machine.

     Andrew