linux-kernel - [PATCH 24/48] rcu: Bring diagnostic read of rcu_state.gp

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Message-Id: <20240507093530.3043-25-urezki@gmail.com>
Date: Tue,  7 May 2024 11:35:06 +0200
From: "Uladzislau Rezki (Sony)" <urezki@...il.com>
To: "Paul E . McKenney" <paulmck@...nel.org>
Cc: RCU <rcu@...r.kernel.org>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Boqun Feng <boqun.feng@...il.com>,
	Hillf Danton <hdanton@...a.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>,
	Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH 24/48] rcu: Bring diagnostic read of rcu_state.gp_flags into alignment

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

This commit adds READ_ONCE() to a lockless diagnostic read from
rcu_state.gp_flags to avoid giving the compiler any chance whatsoever
of confusing the diagnostic state printed.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 kernel/rcu/tree_stall.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 5d666428546b..62b2c4858028 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -579,7 +579,7 @@ static void rcu_check_gp_kthread_expired_fqs_timer(void)
 		pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x\n",
 		       rcu_state.name, (jiffies - jiffies_fqs),
 		       (long)rcu_seq_current(&rcu_state.gp_seq),
-		       data_race(rcu_state.gp_flags),
+		       data_race(READ_ONCE(rcu_state.gp_flags)), // Diagnostic read
 		       gp_state_getname(RCU_GP_WAIT_FQS), RCU_GP_WAIT_FQS,
 		       data_race(READ_ONCE(gpk->__state)));
 		pr_err("\tPossible timer handling issue on cpu=%d timer-softirq=%u\n",
-- 
2.39.2