linux-kernel - [PATCH AUTOSEL 6.10 069/121] thermal: trip: Use READ_ONCE() for lockless access to trip properties

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Message-ID: <20240801000834.3930818-69-sashal@kernel.org>
Date: Wed, 31 Jul 2024 20:00:07 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Sasha Levin <sashal@...nel.org>,
	rafael@...nel.org,
	daniel.lezcano@...aro.org,
	linux-pm@...r.kernel.org
Subject: [PATCH AUTOSEL 6.10 069/121] thermal: trip: Use READ_ONCE() for lockless access to trip properties

From: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>

[ Upstream commit a52641bc6293a24f25956a597e7f32148b0e2bb8 ]

When accessing trip temperature and hysteresis without locking, it is
better to use READ_ONCE() to prevent compiler optimizations possibly
affecting the read from being applied.

Of course, for the READ_ONCE() to be effective, WRITE_ONCE() needs to
be used when updating their values.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/thermal/thermal_sysfs.c | 6 +++---
 drivers/thermal/thermal_trip.c  | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index 88211ccdfbd62..5be6113e7c80f 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -150,7 +150,7 @@ trip_point_temp_show(struct device *dev, struct device_attribute *attr,
 	if (sscanf(attr->attr.name, "trip_point_%d_temp", &trip_id) != 1)
 		return -EINVAL;
 
-	return sprintf(buf, "%d\n", tz->trips[trip_id].trip.temperature);
+	return sprintf(buf, "%d\n", READ_ONCE(tz->trips[trip_id].trip.temperature));
 }
 
 static ssize_t
@@ -174,7 +174,7 @@ trip_point_hyst_store(struct device *dev, struct device_attribute *attr,
 	trip = &tz->trips[trip_id].trip;
 
 	if (hyst != trip->hysteresis) {
-		trip->hysteresis = hyst;
+		WRITE_ONCE(trip->hysteresis, hyst);
 
 		thermal_zone_trip_updated(tz, trip);
 	}
@@ -194,7 +194,7 @@ trip_point_hyst_show(struct device *dev, struct device_attribute *attr,
 	if (sscanf(attr->attr.name, "trip_point_%d_hyst", &trip_id) != 1)
 		return -EINVAL;
 
-	return sprintf(buf, "%d\n", tz->trips[trip_id].trip.hysteresis);
+	return sprintf(buf, "%d\n", READ_ONCE(tz->trips[trip_id].trip.hysteresis));
 }
 
 static ssize_t
diff --git a/drivers/thermal/thermal_trip.c b/drivers/thermal/thermal_trip.c
index 49e63db685172..b4e7411b2fe74 100644
--- a/drivers/thermal/thermal_trip.c
+++ b/drivers/thermal/thermal_trip.c
@@ -152,7 +152,7 @@ void thermal_zone_set_trip_temp(struct thermal_zone_device *tz,
 	if (trip->temperature == temp)
 		return;
 
-	trip->temperature = temp;
+	WRITE_ONCE(trip->temperature, temp);
 	thermal_notify_tz_trip_change(tz, trip);
 
 	if (temp == THERMAL_TEMP_INVALID) {
-- 
2.43.0