linux-kernel - [PATCH 11/16] rcu: Set SEGCBLIST_SOFTIRQ_ONLY at the very last stage of de-offloading

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Message-Id: <20201023144649.53046-12-frederic@kernel.org>
Date:   Fri, 23 Oct 2020 16:46:44 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>
Subject: [PATCH 11/16] rcu: Set SEGCBLIST_SOFTIRQ_ONLY at the very last stage of de-offloading

Set SEGCBLIST_SOFTIRQ_ONLY once everything is settled. After that, the
callbacks are handled locklessly and locally.

Inspired-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Paul E. McKenney <paulmck@...nel.org>
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>
---
 kernel/rcu/tree_plugin.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 49bd42995ae7..2f083beab9d9 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2353,7 +2353,14 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
 	 * enqueued on bypass.
 	 */
 	rcu_nocb_flush_bypass(rdp, NULL, jiffies);
-	rcu_nocb_unlock_irqrestore(rdp, flags);
+	rcu_segcblist_set_flags(cblist, SEGCBLIST_SOFTIRQ_ONLY);
+	/*
+	 * With SEGCBLIST_SOFTIRQ_ONLY, we can't use
+	 * rcu_nocb_unlock_irqrestore() anymore. Theoretically we
+	 * could set SEGCBLIST_SOFTIRQ_ONLY with cb unlocked and IRQs
+	 * disabled now, but let's be paranoid.
+	 */
+	raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 
 	return ret;
 }
-- 
2.25.1