rcu: Fix synchronize_rcu() for TREE_PREEMPT_RCU

The redirection of synchronize_sched() to synchronize_rcu() was
appropriate for TREE_RCU, but not for TREE_PREEMPT_RCU.

Fix this by creating an underlying synchronize_sched().  TREE_RCU
then redirects synchronize_rcu() to synchronize_sched(), while
TREE_PREEMPT_RCU has its own version of synchronize_rcu().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
LKML-Reference: <12528585111916-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index a893077..00d08c0 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -53,6 +53,8 @@
 	preempt_enable();
 }
 
+#define __synchronize_sched() synchronize_rcu()
+
 static inline void exit_rcu(void)
 {
 }
@@ -68,8 +70,6 @@
 	local_bh_enable();
 }
 
-#define __synchronize_sched() synchronize_rcu()
-
 extern void call_rcu_sched(struct rcu_head *head,
 			   void (*func)(struct rcu_head *rcu));