linux-kernel - [tip: core/rcu] rcu/nocb: Flush bypass before setting SEGCBLIST_SOFTIRQ

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Message-ID: <161313343880.23325.18244968176863208111.tip-bot2@tip-bot2>
Date:   Fri, 12 Feb 2021 12:37:18 -0000
From:   "tip-bot2 for Frederic Weisbecker" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Boqun Feng <boqun.feng@...il.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: core/rcu] rcu/nocb: Flush bypass before setting SEGCBLIST_SOFTIRQ_ONLY

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

Commit-ID:     314202f84ddd61e4d7576ef62570ad2e2d9db06b
Gitweb:        https://git.kernel.org/tip/314202f84ddd61e4d7576ef62570ad2e2d9db06b
Author:        Frederic Weisbecker <frederic@...nel.org>
AuthorDate:    Fri, 13 Nov 2020 13:13:24 +01:00
Committer:     Paul E. McKenney <paulmck@...nel.org>
CommitterDate: Wed, 06 Jan 2021 16:24:59 -08:00

rcu/nocb: Flush bypass before setting SEGCBLIST_SOFTIRQ_ONLY

This commit flushes the bypass queue and sets state to avoid its being
refilled before switching to the final de-offloaded state.  To avoid
refilling, this commit sets SEGCBLIST_SOFTIRQ_ONLY before re-enabling
IRQs.

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>
Cc: Neeraj Upadhyay <neeraju@...eaurora.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Inspired-by: Paul E. McKenney <paulmck@...nel.org>
Tested-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree_plugin.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c88ad62..35dc9b3 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2339,12 +2339,21 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
 	swait_event_exclusive(rdp->nocb_state_wq,
 			      !rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB |
 							SEGCBLIST_KTHREAD_GP));
-	/* Make sure nocb timer won't stay around */
 	rcu_nocb_lock_irqsave(rdp, flags);
+	/* Make sure nocb timer won't stay around */
 	WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_OFF);
 	rcu_nocb_unlock_irqrestore(rdp, flags);
 	del_timer_sync(&rdp->nocb_timer);
 
+	/*
+	 * Flush bypass. While IRQs are disabled and once we set
+	 * SEGCBLIST_SOFTIRQ_ONLY, no callback is supposed to be
+	 * enqueued on bypass.
+	 */
+	rcu_nocb_lock_irqsave(rdp, flags);
+	rcu_nocb_flush_bypass(rdp, NULL, jiffies);
+	rcu_nocb_unlock_irqrestore(rdp, flags);
+
 	return ret;
 }