linux-kernel - [PATCH v3 7/9] thermal/sysfs: Update instance->weight under tz lock

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Message-Id: <20231220231753.1824364-8-lukasz.luba@arm.com>
Date: Wed, 20 Dec 2023 23:17:51 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: linux-kernel@...r.kernel.org,
	rafael@...nel.org
Cc: linux-pm@...r.kernel.org,
	daniel.lezcano@...aro.org,
	rui.zhang@...el.com,
	lukasz.luba@....com
Subject: [PATCH v3 7/9] thermal/sysfs: Update instance->weight under tz lock

User space can change the weight of a thermal instance via sysfs while the
.throttle() callback is running for a governor, because weight_store()
does not use the zone lock.

The IPA governor uses instance weight values for power calculations and
caches the sum of them as total_weight, so it gets confused when one of
them changes while its .throttle() callback is running.

To prevent that from happening, use thermal zone locking in
weight_store().

Signed-off-by: Lukasz Luba <lukasz.luba@....com>
---
 drivers/thermal/thermal_sysfs.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index d8ff74a4338a..299c0fb16593 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -936,7 +936,11 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
 		return ret;
 
 	instance = container_of(attr, struct thermal_instance, weight_attr);
+
+	/* Don't race with governors using the 'weight' value */
+	mutex_lock(&instance->tz->lock);
 	instance->weight = weight;
+	mutex_unlock(&instance->tz->lock);
 
 	return count;
 }
-- 
2.25.1