[PATCH RFC tip/core/rcu 7/7] rcu: Quiet RCU-lockdep warnings involving interrupt disabling

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

From: Yong Zhang <yong.zhang0@gmail.com>

RCU-lockdep will issue warnings given the following use pattern:

	rcu_read_lock();
	local_irq_disable();
	rcu_read_unlock();
	local_irq_enable();

However, this use pattern is legal except for the scheduler's runqueue
and priority-inheritance locks (and any other locks that the scheduler
might use during priority-inheritance operations).

Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutree_plugin.h |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 8cd9efe..2020e8a 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -401,8 +401,11 @@ static noinline void rcu_read_unlock_special(struct task_struct *t)
 
 #ifdef CONFIG_RCU_BOOST
 		/* Unboost if we were boosted. */
-		if (rbmp)
+		if (rbmp) {
+			local_irq_save(flags);
 			rt_mutex_unlock(rbmp);
+			local_irq_restore(flags);
+		}
 #endif /* #ifdef CONFIG_RCU_BOOST */
 
 		/*
@@ -1233,9 +1236,10 @@ static int rcu_boost(struct rcu_node *rnp)
 	lockdep_set_class_and_name(&mtx.wait_lock, &rcu_boost_class,
 				   "rcu_boost_mutex");
 	t->rcu_boost_mutex = &mtx;
-	raw_spin_unlock_irqrestore(&rnp->lock, flags);
+	raw_spin_unlock(&rnp->lock); /* rrupts remain disabled. */
 	rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
 	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
+	local_irq_restore(flags);
 
 	return rnp->exp_tasks != NULL || rnp->boost_tasks != NULL;
 }
-- 
1.7.3.2