linux-kernel - [PATCH 11/13] rcu/nocb: Only cancel nocb timer if not polling

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Date:   Tue, 23 Feb 2021 01:10:09 +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>,
        Thomas Gleixner <tglx@...utronix.de>,
        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 11/13] rcu/nocb: Only cancel nocb timer if not polling

No need to disarm the nocb_timer if rcu_nocb is polling because it
shouldn't be armed either.

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 | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 9da67b0d3997..d8b50ff40e4b 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2186,18 +2186,18 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 	my_rdp->nocb_gp_gp = needwait_gp;
 	my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
 	if (bypass) {
-		raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
-		// Avoid race with first bypass CB.
-		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);
-		}
 		if (!rcu_nocb_poll) {
+			raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
+			// Avoid race with first bypass CB.
+			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);
+			}
 			// At least one child with non-empty ->nocb_bypass, so set
 			// timer in order to avoid stranding its callbacks.
 			mod_timer(&my_rdp->nocb_bypass_timer, j + 2);
+			raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
 		}
-		raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
 	}
 	if (rcu_nocb_poll) {
 		/* Polling, so trace if first poll in the series. */
-- 
2.25.1