static void opt_kfree_rcu(struct rcu_head *head)
{
	kfree(container_of(head, struct ip_options_rcu, rcu));
}
The program contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.