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From:   Lukasz Luba <lukasz.luba@arm.com>
To:     linux-kernel@vger.kernel.org, daniel.lezcano@linaro.org,
        rafael@kernel.org
Cc:     linux-pm@vger.kernel.org, rui.zhang@intel.com, lukasz.luba@arm.com
Subject: [PATCH v2 6/8] thermal/sysfs: Update instance->weight under tz lock
Date:   Tue, 12 Dec 2023 13:48:42 +0000
Message-Id: <20231212134844.1213381-7-lukasz.luba@arm.com>
In-Reply-To: <20231212134844.1213381-1-lukasz.luba@arm.com>
References: <20231212134844.1213381-1-lukasz.luba@arm.com>
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The user-space can change thermal instance weight value while the
throtte() callback is running for a governor. The IPA governor uses the
'weight' value for power calculation and also keeps it in 'total_weight'.
Therefore, the 'weight' value must not change during the throttle()
callback. Use 'tz->lock' mutex which also guards the throttle() to make
the update value safe.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
---
 drivers/thermal/thermal_sysfs.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index eef40d4f3063..df85df7d4a88 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -961,6 +961,7 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
 		     const char *buf, size_t count)
 {
 	struct thermal_instance *instance;
+	struct thermal_zone_device *tz;
 	int ret, weight;
 
 	ret = kstrtoint(buf, 0, &weight);
@@ -968,7 +969,12 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
 		return ret;
 
 	instance = container_of(attr, struct thermal_instance, weight_attr);
+	tz = instance->tz;
+
+	/* Don't race with governors using the 'weight' value */
+	mutex_lock(&tz->lock);
 	instance->weight = weight;
+	mutex_unlock(&tz->lock);
 
 	return count;
 }
-- 
2.25.1