[tip: core/rcu] rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup

[tip: core/rcu] rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup

[tip-bot2 for Frederic Weisbecker]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     b6e2c4ed35c33d7e55197aa26d99645a690ca467
Gitweb:        https://git.kernel.org/tip/b6e2c4ed35c33d7e55197aa26d99645a690ca467
Author:        Frederic Weisbecker <frederic@kernel.org>
AuthorDate:    Tue, 23 Feb 2021 01:10:07 +01:00
Committer:     Paul E. McKenney <paulmck@kernel.org>
CommitterDate: Wed, 12 May 2021 12:10:23 -07:00

rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup

When waking up in nocb_gp_wait(), there is no need to keep the nocb_timer
around because this function will traverse the whole rdp list. Any
update performed before the timer was armed will now be visible after
the ->nocb_gp_lock acquire.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 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 015adec..a667551 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2211,6 +2211,10 @@ 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);
 	}