Callback Handling
x	__call_rcu(),
x	cpu_has_callbacks_ready_to_invoke(),
	rcu_start_gp_per_cpu(),
	rcu_report_qs_rdp(),
	__rcu_process_gp_end(!)
x	invoke_rcu_callbacks(),
	__rcu_reclaim(),
	rcu_do_batch(),
	rcu_preempt_do_callbacks(),
x	rcu_barrier_callback(),
	rcu_barrier_func(),
	_rcu_barrier(),
x	rcu_send_cbs_to_online(),
	rcu_preempt_send_cbs_to_online(),
