rcu: Define RCU-bh update API in terms of RCU

Now that the main RCU API knows about softirq disabling and softirq's
quiescent states, the RCU-bh update code can be dispensed with.
This commit therefore removes the RCU-bh update-side implementation and
defines RCU-bh's update-side API in terms of that of either RCU-preempt or
RCU-sched, depending on the setting of the CONFIG_PREEMPT Kconfig option.

In kernels built with CONFIG_RCU_NOCB_CPU=y this has the knock-on effect
of reducing by one the number of rcuo kthreads per CPU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

3 files changed, 19 insertions, 9 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 75e5b393cf44..9ebfd436cec7 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -55,11 +55,15 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func);
 #define	call_rcu	call_rcu_sched
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
-void call_rcu_bh(struct rcu_head *head, rcu_callback_t func);
 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func);
 void synchronize_sched(void);
 void rcu_barrier_tasks(void);
 
+static inline void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
+{
+	call_rcu(head, func);
+}
+
 #ifdef CONFIG_PREEMPT_RCU
 
 void __rcu_read_lock(void);
@@ -104,7 +108,6 @@ static inline int rcu_preempt_depth(void)
 void rcu_init(void);
 extern int rcu_scheduler_active __read_mostly;
 void rcu_sched_qs(void);
-void rcu_bh_qs(void);
 void rcu_check_callbacks(int user);
 void rcu_report_dead(unsigned int cpu);
 void rcutree_migrate_callbacks(int cpu);
@@ -326,8 +329,7 @@ static inline void rcu_preempt_sleep_check(void) { }
  * 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_bh, * __rcu_sched, and __srcu), should this make sense in
- * the future.
+ * (e.g., __rcu_sched, and __srcu), should this make sense in the future.
  */
 
 #ifdef __CHECKER__
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index bcfbc40a7239..ac26c27ccde8 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -56,19 +56,23 @@ static inline void cond_synchronize_sched(unsigned long oldstate)
 	might_sleep();
 }
 
-extern void rcu_barrier_bh(void);
-extern void rcu_barrier_sched(void);
-
 static inline void synchronize_rcu_expedited(void)
 {
 	synchronize_sched();	/* Only one CPU, so pretty fast anyway!!! */
 }
 
+extern void rcu_barrier_sched(void);
+
 static inline void rcu_barrier(void)
 {
 	rcu_barrier_sched();  /* Only one CPU, so only one list of callbacks! */
 }
 
+static inline void rcu_barrier_bh(void)
+{
+	rcu_barrier();
+}
+
 static inline void synchronize_rcu_bh(void)
 {
 	synchronize_sched();
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 664b580695d6..c789c302a2c9 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -45,7 +45,11 @@ static inline void rcu_virt_note_context_switch(int cpu)
 	rcu_note_context_switch(false);
 }
 
-void synchronize_rcu_bh(void);
+static inline void synchronize_rcu_bh(void)
+{
+	synchronize_rcu();
+}
+
 void synchronize_sched_expedited(void);
 void synchronize_rcu_expedited(void);
 
@@ -69,7 +73,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
  */
 static inline void synchronize_rcu_bh_expedited(void)
 {
-	synchronize_sched_expedited();
+	synchronize_rcu_expedited();
 }
 
 void rcu_barrier(void);