head = rcu_dereference(s->head);
if (head) {
struct cds_lfs_node_rcu *next = rcu_dereference(head->next);
if (uatomic_cmpxchg(&s->head, head, next) == head) {
head = rcu_dereference(s->head);
if (head) {
struct cds_lfs_node_rcu *next = rcu_dereference(head->next);
if (uatomic_cmpxchg(&s->head, head, next) == head) {