linux-kernel - [PATCH 03/10] rcu: Make locking explicit in do_nocb_deferred_wakeup

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Date:   Wed, 13 May 2020 18:47:07 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E . McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>
Subject: [PATCH 03/10] rcu: Make locking explicit in do_nocb_deferred_wakeup_common()

It can either be called inline (locally or CPU hotplug locked) when
rdp->nocb_defer_wakeup is pending or from the nocb timer. In both cases
the rdp is offlined and we want to take the nocb lock.

Clarify the locking rules and expectations.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Paul E. McKenney <paulmck@...nel.org>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
---
 kernel/rcu/tree_plugin.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1d22b16c03e0..1dd3fdd675a1 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2142,9 +2142,9 @@ static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
 	unsigned long flags;
 	int ndw;
 
-	rcu_nocb_lock_irqsave(rdp, flags);
+	raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
 	if (!rcu_nocb_need_deferred_wakeup(rdp)) {
-		rcu_nocb_unlock_irqrestore(rdp, flags);
+		raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 		return;
 	}
 	ndw = READ_ONCE(rdp->nocb_defer_wakeup);
-- 
2.25.0