rcu: Define RCU-sched API in terms of RCU for Tree RCU PREEMPT builds

Now that RCU-preempt knows about preemption disabling, its implementation
of synchronize_rcu() works for synchronize_sched(), and likewise for the
other RCU-sched update-side API members.  This commit therefore confines
the RCU-sched update-side code to CONFIG_PREEMPT=n builds, and defines
RCU-sched's update-side API members in terms of those of RCU-preempt.

This means that any given build of the Linux kernel has only one
update-side flavor of RCU, namely RCU-preempt for CONFIG_PREEMPT=y builds
and RCU-sched for CONFIG_PREEMPT=n builds.  This in turn means that kernels
built with CONFIG_RCU_NOCB_CPU=y have only one rcuo kthread per CPU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>

include/linux/rcupdate.h

@@ -49,11 +49,11 @@
 
 /* Exported common interfaces */
 
-#ifdef CONFIG_PREEMPT_RCU
-void call_rcu(struct rcu_head *head, rcu_callback_t func);
-#else /* #ifdef CONFIG_PREEMPT_RCU */
+#ifdef CONFIG_TINY_RCU
 #define	call_rcu	call_rcu_sched
-#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+#else
+void call_rcu(struct rcu_head *head, rcu_callback_t func);
+#endif
 
 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func);
 void synchronize_sched(void);
@@ -92,11 +92,6 @@ static inline void __rcu_read_unlock(void)
 		preempt_enable();
 }
 
-static inline void synchronize_rcu(void)
-{
-	synchronize_sched();
-}
-
 static inline int rcu_preempt_depth(void)
 {
 	return 0;
@@ -107,7 +102,6 @@ static inline int rcu_preempt_depth(void)
 /* Internal to kernel */
 void rcu_init(void);
 extern int rcu_scheduler_active __read_mostly;
-void rcu_sched_qs(void);
 void rcu_check_callbacks(int user);
 void rcu_report_dead(unsigned int cpu);
 void rcutree_migrate_callbacks(int cpu);

include/linux/rcutiny.h

@@ -36,6 +36,11 @@ static inline int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
 /* Never flag non-existent other CPUs! */
 static inline bool rcu_eqs_special_set(int cpu) { return false; }
 
+static inline void synchronize_rcu(void)
+{
+	synchronize_sched();
+}
+
 static inline unsigned long get_state_synchronize_rcu(void)
 {
 	return 0;
@@ -94,6 +99,8 @@ static inline void kfree_call_rcu(struct rcu_head *head,
 	call_rcu(head, func);
 }
 
+void rcu_sched_qs(void);
+
 static inline void rcu_softirq_qs(void)
 {
 	rcu_sched_qs();

include/linux/rcutree.h

@@ -45,14 +45,19 @@ static inline void rcu_virt_note_context_switch(int cpu)
 	rcu_note_context_switch(false);
 }
 
+void synchronize_rcu(void);
 static inline void synchronize_rcu_bh(void)
 {
 	synchronize_rcu();
 }
 
-void synchronize_sched_expedited(void);
 void synchronize_rcu_expedited(void);
 
+static inline void synchronize_sched_expedited(void)
+{
+	synchronize_rcu_expedited();
+}
+
 void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
 
 /**