percpu_ref_switch_to_atomic_sync
percpu_ref_switch_to_atomic_sync(&q->q_usage_counter);
percpu_ref_switch_to_atomic_sync(&mddev->writes_pending);
void percpu_ref_switch_to_atomic_sync(struct percpu_ref *ref);
EXPORT_SYMBOL_GPL(percpu_ref_switch_to_atomic_sync);