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>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index ac26c27ccde8..df2c0895c5e7 100644
--- a/include/linux/rcutiny.h
+++ b/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();