linux-kernel - [PATCH] rcu: Use READ_ONCE() for rdp->gpwrap access in __note_gp

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Message-Id: <20241104151230.3107133-1-zilinguan811@gmail.com>
Date: Mon,  4 Nov 2024 15:12:30 +0000
From: Zilin Guan <zilinguan811@...il.com>
To: paulmck@...nel.org
Cc: frederic@...nel.org,
	neeraj.upadhyay@...nel.org,
	joel@...lfernandes.org,
	josh@...htriplett.org,
	boqun.feng@...il.com,
	urezki@...il.com,
	rostedt@...dmis.org,
	mathieu.desnoyers@...icios.com,
	jiangshanlai@...il.com,
	qiang.zhang1211@...il.com,
	rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Zilin Guan <zilinguan811@...il.com>
Subject: [PATCH] rcu: Use READ_ONCE() for rdp->gpwrap access in __note_gp_changes()

In function __note_gp_changes(), rdp->gpwrap is read using READ_ONCE()
in line 1307:

1307    if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
1308            WRITE_ONCE(rdp->last_sched_clock, jiffies);

while read directly in line 1305:

1305    if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) ||
	    rdp->gpwrap)
1306            WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);

In the same environment, reads in two places should have the same
protection.

Signed-off-by: Zilin Guan <zilinguan811@...il.com>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b1f883fcd918..d3e2b420dce5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1302,7 +1302,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
 		zero_cpu_stall_ticks(rdp);
 	}
 	rdp->gp_seq = rnp->gp_seq;  /* Remember new grace-period state. */
-	if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
+	if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || READ_ONCE(rdp->gpwrap))
 		WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
 	if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
 		WRITE_ONCE(rdp->last_sched_clock, jiffies);
-- 
2.34.1