Quiescent State Detection
API:	rcu_sched_qs(), rcu_bh_qs(), rcu_note_context_switch(),
	rcu_check_callbacks(), rcu_virt_note_context_switch(),

Others:	rcu_preempt_qs(),
	rcu_preempt_note_context_switch(),
	rcu_preempt_check_callbacks(),
