[PATCH RFC 05/16] rcu: introduce rcu_defer_qs_clear() helper

["Paul E. McKenney" <paulmck@kernel.org>]

From: Joel Fernandes <joelagnelf@nvidia.com>

Currently rdp->defer_qs_pending transitions from DEFER_QS_PENDING to
DEFER_QS_IDLE at two sites: rcu_preempt_deferred_qs_irqrestore() and
rcu_preempt_deferred_qs_handler() (depth>0 reset).  Both write the
IDLE value directly.

Introduce a single inline helper rcu_defer_qs_clear() in tree.h and
route both sites through it.  This becomes the single
PENDING->IDLE transition point for upcoming work.

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.h        | 5 +++++
 kernel/rcu/tree_plugin.h | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 7dfc57e9adb18e..4069132f9d4446 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -296,6 +296,11 @@ struct rcu_data {
 	int cpu;
 };
 
+static inline void rcu_defer_qs_clear(struct rcu_data *rdp)
+{
+	WRITE_ONCE(rdp->defer_qs_pending, DEFER_QS_IDLE);
+}
+
 /* Values for nocb_defer_wakeup field in struct rcu_data. */
 #define RCU_NOCB_WAKE_NOT	0
 #define RCU_NOCB_WAKE_BYPASS	1
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 95ad967adcf3cb..8637f405cb472f 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -488,7 +488,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 
 	rdp = this_cpu_ptr(&rcu_data);
 	if (rdp->defer_qs_pending == DEFER_QS_PENDING)
-		rdp->defer_qs_pending = DEFER_QS_IDLE;
+		rcu_defer_qs_clear(rdp);
 
 	/*
 	 * If RCU core is waiting for this CPU to exit its critical section,
@@ -645,7 +645,7 @@ static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
 	 * 5. Deferred QS reporting does not happen.
 	 */
 	if (rcu_preempt_depth() > 0)
-		WRITE_ONCE(rdp->defer_qs_pending, DEFER_QS_IDLE);
+		rcu_defer_qs_clear(rdp);
 }
 
 /*
-- 
2.40.1