linux-kernel - [tip: core/rcu] rcu/nocb: Only cancel nocb timer if not polling

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Message-ID: <162506084839.395.10133057189448756080.tip-bot2@tip-bot2>
Date:   Wed, 30 Jun 2021 13:47:28 -0000
From:   "tip-bot2 for Frederic Weisbecker" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: core/rcu] rcu/nocb: Only cancel nocb timer if not polling

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

Commit-ID:     f9fc166b790bd214083035d865653133b8a963d1
Gitweb:        https://git.kernel.org/tip/f9fc166b790bd214083035d865653133b8a963d1
Author:        Frederic Weisbecker <frederic@...nel.org>
AuthorDate:    Tue, 23 Feb 2021 01:10:09 +01:00
Committer:     Paul E. McKenney <paulmck@...nel.org>
CommitterDate: Wed, 12 May 2021 12:10:23 -07:00

rcu/nocb: Only cancel nocb timer if not polling

This commit refrains deleting the ->nocb_timer if rcu_nocb is polling
because it should not ever have been queued in the polling case.

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>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 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 4253a0e..db28e31 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2176,18 +2176,18 @@ 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. */