linux-kernel - [PATCH 12/16] rcu/nocb: Cancel nocb_timer upon nocb

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Date:   Thu, 28 Jan 2021 18:12:18 +0100
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>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Stable <stable@...r.kernel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH 12/16] rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup

As we wake up in nocb_gp_wait(), there is no need to keep the nocb_timer
around as we are going to go through the whole rdp list again. Any update
performed before the timer was armed will now be visible after the
nocb_gp_lock acquire.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Neeraj Upadhyay <neeraju@...eaurora.org>
Cc: Boqun Feng <boqun.feng@...il.com>
---
 kernel/rcu/tree_plugin.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index dae892ac570a..39fb792704ed 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2212,6 +2212,10 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 		raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
 		if (bypass)
 			del_timer(&my_rdp->nocb_bypass_timer);
+		if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
+			WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
+			del_timer(&my_rdp->nocb_timer);
+		}
 		WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
 		raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
 	}
-- 
2.25.1