[PATCH tip/core/rcu 3/6] rcu: stopgap fix for synchronize_rcu_expedited() for TREE_PREEMPT_RCU

[Paul E. McKenney]

From: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

For the short term, map synchronize_rcu_expedited() to synchronize_rcu()
for TREE_PREEMPT_RCU and to synchronize_sched_expedited() for TREE_RCU.
Longer term, there needs to be a real expedited grace period for
TREE_PREEMPT_RCU, but candidate patches to date are considerably more
complex and intrusive.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 include/linux/rcutree.h |    6 +-----
 kernel/rcutree_plugin.h |   19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 46e9ab3..9642c6b 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -76,11 +76,7 @@ static inline void __rcu_read_unlock_bh(void)
 
 extern void call_rcu_sched(struct rcu_head *head,
 			   void (*func)(struct rcu_head *rcu));
-
-static inline void synchronize_rcu_expedited(void)
-{
-	synchronize_sched_expedited();
-}
+extern void synchronize_rcu_expedited(void);
 
 static inline void synchronize_rcu_bh_expedited(void)
 {
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index c0cb783..acef871 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -393,6 +393,16 @@ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 EXPORT_SYMBOL_GPL(call_rcu);
 
 /*
+ * Wait for an rcu-preempt grace period.  We are supposed to expedite the
+ * grace period, but this is the crude slow compatability hack, so just
+ * invoke synchronize_rcu().
+ */
+void synchronize_rcu_expedited(void)
+{
+	synchronize_rcu();
+}
+
+/*
  * Check to see if there is any immediate preemptable-RCU-related work
  * to be done.
  */
@@ -565,6 +575,15 @@ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 EXPORT_SYMBOL_GPL(call_rcu);
 
 /*
+ * Wait for an rcu-preempt grace period, but make it happen quickly.
+ * But because preemptable RCU does not exist, map to rcu-sched.
+ */
+void synchronize_rcu_expedited(void)
+{
+	synchronize_sched_expedited();
+}
+
+/*
  * Because preemptable RCU does not exist, it never has any work to do.
  */
 static int rcu_preempt_pending(int cpu)
-- 
1.5.2.5

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