linux-kernel - [PATCH AUTOSEL 6.4 3/4] rcu: Mark rcu_cpu_kthread() accesses to ->rcu_cpu_has

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Message-Id: <20230702195743.1793074-3-sashal@kernel.org>
Date:   Sun,  2 Jul 2023 15:57:41 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Sasha Levin <sashal@...nel.org>, frederic@...nel.org,
        quic_neeraju@...cinc.com, joel@...lfernandes.org,
        josh@...htriplett.org, boqun.feng@...il.com, rcu@...r.kernel.org
Subject: [PATCH AUTOSEL 6.4 3/4] rcu: Mark rcu_cpu_kthread() accesses to ->rcu_cpu_has_work

From: "Paul E. McKenney" <paulmck@...nel.org>

[ Upstream commit a24c1aab652ebacf9ea62470a166514174c96fe1 ]

The rcu_data structure's ->rcu_cpu_has_work field can be modified by
any CPU attempting to wake up the rcuc kthread.  Therefore, this commit
marks accesses to this field from the rcu_cpu_kthread() function.

This data race was reported by KCSAN.  Not appropriate for backporting
due to failure being unlikely.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/rcu/tree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f52ff72410416..fe649dd0165c3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2459,12 +2459,12 @@ static void rcu_cpu_kthread(unsigned int cpu)
 		*statusp = RCU_KTHREAD_RUNNING;
 		local_irq_disable();
 		work = *workp;
-		*workp = 0;
+		WRITE_ONCE(*workp, 0);
 		local_irq_enable();
 		if (work)
 			rcu_core();
 		local_bh_enable();
-		if (*workp == 0) {
+		if (!READ_ONCE(*workp)) {
 			trace_rcu_utilization(TPS("End CPU kthread@..._wait"));
 			*statusp = RCU_KTHREAD_WAITING;
 			return;
-- 
2.39.2