linux-kernel - [PATCH rcu 01/10] rcu: Mark accesses to boost

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Date:   Fri,  4 Feb 2022 15:23:57 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 01/10] rcu: Mark accesses to boost_starttime

The boost_starttime shared variable has conflicting unmarked C-language
accesses, which are dangerous at best.  This commit therefore adds
appropriate marking.  This was found by KCSAN.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/rcutorture.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 422f7e4cc08de..829ae0b7d3c04 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -997,7 +997,7 @@ static int rcu_torture_boost(void *arg)
 			goto checkwait;
 
 		/* Wait for the next test interval. */
-		oldstarttime = boost_starttime;
+		oldstarttime = READ_ONCE(boost_starttime);
 		while (time_before(jiffies, oldstarttime)) {
 			schedule_timeout_interruptible(oldstarttime - jiffies);
 			if (stutter_wait("rcu_torture_boost"))
@@ -1041,10 +1041,11 @@ static int rcu_torture_boost(void *arg)
 		 * interval.  Besides, we are running at RT priority,
 		 * so delays should be relatively rare.
 		 */
-		while (oldstarttime == boost_starttime && !kthread_should_stop()) {
+		while (oldstarttime == READ_ONCE(boost_starttime) && !kthread_should_stop()) {
 			if (mutex_trylock(&boost_mutex)) {
 				if (oldstarttime == boost_starttime) {
-					boost_starttime = jiffies + test_boost_interval * HZ;
+					WRITE_ONCE(boost_starttime,
+						   jiffies + test_boost_interval * HZ);
 					n_rcu_torture_boosts++;
 				}
 				mutex_unlock(&boost_mutex);
-- 
2.31.1.189.g2e36527f23