linux_synchronize_rcu
void linux_synchronize_rcu(unsigned type);
linux_synchronize_rcu(RCU_TYPE_REGULAR); \
linux_synchronize_rcu(RCU_TYPE_REGULAR); \
linux_synchronize_rcu(RCU_TYPE_REGULAR);
linux_synchronize_rcu(head - linux_epoch_head);
linux_synchronize_rcu(RCU_TYPE_SLEEPABLE);