force_mb_single_thread(index); /* Write futex before read reader_gp */
if (!rcu_old_gp_ongoing(index->urcu_active_readers)) {
/* Read reader_gp before write futex */
force_mb_single_thread(index);
/* Callbacks are queued, don't wait. */
force_mb_single_thread(index); /* Write futex before read reader_gp */
if (!rcu_old_gp_ongoing(index->urcu_active_readers)) {
/* Read reader_gp before write futex */
force_mb_single_thread(index);
/* Callbacks are queued, don't wait. */