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Message-ID: <tencent_B51A9DA220288A95A435E3435A0443BEB007@qq.com>
From: linke li <lilinke99@qq.com>
To: 
Cc: lilinke99@qq.com,
	Davidlohr Bueso <dave@stgolabs.net>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Neeraj Upadhyay <quic_neeraju@quicinc.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	Boqun Feng <boqun.feng@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Zqiang <qiang.zhang1211@gmail.com>,
	linux-kernel@vger.kernel.org,
	rcu@vger.kernel.org
Subject: [PATCH] rcutorture: Fix rcu_torture_pipe_update_one()/rcu_torture_writer() data race and concurrency bug
Date: Mon,  4 Mar 2024 18:54:46 +0800
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Some changes are done to fix a data race in commit 202489101f2e ("rcutorture: Fix rcu_torture_one_read()/rcu_torture_writer() data race")

 {
 	int i;

-	i = rp->rtort_pipe_count;
+	i = READ_ONCE(rp->rtort_pipe_count);
 	if (i > RCU_TORTURE_PIPE_LEN)
 		i = RCU_TORTURE_PIPE_LEN;
 	atomic_inc(&rcu_torture_wcount[i]);
-	if (++rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
+	WRITE_ONCE(rp->rtort_pipe_count, i + 1);
+	if (rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
 		rp->rtort_mbtest = 0;
 		return true;
 	}

But ++rp->rtort_pipe_count is meant to add itself by 1, not give i+1 to
rp->rtort_pipe_count, because rp->rtort_pipe_count may write by
rcu_torture_writer() concurrently.

Also, rp->rtort_pipe_count in the next line should be read using
READ_ONCE() because of data race.

Signed-off-by: linke li <lilinke99@qq.com>
---
 kernel/rcu/rcutorture.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 7567ca8e743c..00059ace4fd5 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -465,8 +465,8 @@ rcu_torture_pipe_update_one(struct rcu_torture *rp)
 	if (i > RCU_TORTURE_PIPE_LEN)
 		i = RCU_TORTURE_PIPE_LEN;
 	atomic_inc(&rcu_torture_wcount[i]);
-	WRITE_ONCE(rp->rtort_pipe_count, i + 1);
-	if (rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
+	WRITE_ONCE(rp->rtort_pipe_count, rp->rtort_pipe_count + 1);
+	if (READ_ONCE(rp->rtort_pipe_count) >= RCU_TORTURE_PIPE_LEN) {
 		rp->rtort_mbtest = 0;
 		return true;
 	}
-- 
2.39.3 (Apple Git-145)