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>

1 files changed, 7 insertions, 3 deletions

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();