rcu: Clean up flavor-related definitions and comments in rcupdate.h

 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers

 * @a: Code that RCU needs to pay attention to.

 *

 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden

 * in the inner idle loop, that is, between the rcu_idle_enter() and

 * the rcu_idle_exit() -- RCU will happily ignore any such read-side

 * critical sections.  However, things like powertop need tracepoints

 * in the inner idle loop.

 * RCU read-side critical sections are forbidden in the inner idle loop,

 * that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU

 * will happily ignore any such read-side critical sections.  However,

 * things like powertop need tracepoints in the inner idle loop.

 *

 * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())

 * will tell RCU that it needs to pay attention, invoke its argument

#else /* #ifdef CONFIG_TASKS_RCU */

#define rcu_tasks_qs(t)	do { } while (0)

#define rcu_note_voluntary_context_switch(t)		rcu_all_qs()

#define call_rcu_tasks call_rcu_sched

#define call_rcu_tasks call_rcu

#define synchronize_rcu_tasks synchronize_rcu

static inline void exit_tasks_rcu_start(void) { }

static inline void exit_tasks_rcu_finish(void) { }

 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()

 * and rcu_assign_pointer().  Some of these could be folded into their

 * callers, but they are left separate in order to ease introduction of

 * multiple flavors of pointers to match the multiple flavors of RCU

 * (e.g., __rcu_sched, and __srcu), should this make sense in the future.

 * multiple pointers markings to match different RCU implementations

 * (e.g., __srcu), should this make sense in the future.

 */

#ifdef __CHECKER__

 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section

 *

 * This is equivalent of rcu_read_lock(), but also disables softirqs.

 * Note that synchronize_rcu() and friends may be used for the update

 * side, although synchronize_rcu_bh() is available as a wrapper in the

 * short term.  Longer term, the _bh update-side API will be eliminated.

 * Note that anything else that disables softirqs can also serve as

 * an RCU read-side critical section.

 *

 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()

 * must occur in the same context, for example, it is illegal to invoke

/**

 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section

 *

 * This is equivalent of rcu_read_lock(), but to be used when updates

 * are being done using call_rcu_sched() or synchronize_rcu_sched().

 * Read-side critical sections can also be introduced by anything that

 * disables preemption, including local_irq_disable() and friends.

 * This is equivalent of rcu_read_lock(), but disables preemption.

 * Read-side critical sections can also be introduced by anything else

 * that disables preemption, including local_irq_disable() and friends.

 *

 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()

 * must occur in the same context, for example, it is illegal to invoke