[PATCH 4/4] hwmon: (gpd-fan): fix race condition between device removal and sysfs access

[xiaopeitux]

From: Pei Xiao <xiaopei01@xxxxxxxxxx>

Replace the manual gpd_fan_remove() callback with a devres-managed
action using devm_add_action_or_reset(). The original remove hook
resets the fan to AUTOMATIC mode, but the hwmon sysfs interface
(registered with devm_hwmon_device_register_with_info()) remains
active until after the remove callback completes. This creates a
race window where a concurrent userspace sysfs access can interleave
with the EC I/O sequence, potentially corrupting EC registers.

Using devm_add_action_or_reset() registers the reset function as a
devres action. Due to the LIFO release order of devres, the hwmon
device is unregistered (sysfs removed) before the reset action
executes, eliminating the race condition.

Fixes: 0ab88e239439 ("hwmon: add GPD devices sensor driver")
Signed-off-by: Pei Xiao <xiaopei01@xxxxxxxxxx>
---
 drivers/hwmon/gpd-fan.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/hwmon/gpd-fan.c b/drivers/hwmon/gpd-fan.c
index 1b57a5add934..d1993cd645cb 100644
--- a/drivers/hwmon/gpd-fan.c
+++ b/drivers/hwmon/gpd-fan.c
@@ -609,6 +609,16 @@ static void gpd_init_ec(struct gpd_fan_data *data)
 		gpd_win4_init_ec(data);
 }
 
+static void gpd_fan_reset_hardware(void *pdata)
+{
+	struct gpd_fan_data *data = pdata;
+
+	if (data) {
+		data->pwm_enable = AUTOMATIC;
+		gpd_set_pwm_enable(data, AUTOMATIC);
+	}
+}
+
 static int gpd_fan_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -617,6 +627,7 @@ static int gpd_fan_probe(struct platform_device *pdev)
 	struct device *hwdev;
 	struct gpd_fan_data *data;
 	const struct gpd_fan_drvdata *match;
+	int ret;
 
 	res = platform_get_resource(pdev, IORESOURCE_IO, 0);
 	if (!res)
@@ -644,6 +655,11 @@ static int gpd_fan_probe(struct platform_device *pdev)
 	dev_set_drvdata(dev, data);
 
 	gpd_init_ec(data);
+
+	ret = devm_add_action_or_reset(dev, gpd_fan_reset_hardware, data);
+	if (ret)
+		return ret;
+
 	hwdev = devm_hwmon_device_register_with_info(dev,
 						     DRIVER_NAME,
 						     data,
@@ -655,19 +671,8 @@ static int gpd_fan_probe(struct platform_device *pdev)
 	return 0;
 }
 
-static void gpd_fan_remove(struct platform_device *pdev)
-{
-	struct gpd_fan_data *data = dev_get_drvdata(&pdev->dev);
-
-	if (data) {
-		data->pwm_enable = AUTOMATIC;
-		gpd_set_pwm_enable(data, AUTOMATIC);
-	}
-}
-
 static struct platform_driver gpd_fan_driver = {
 	.probe = gpd_fan_probe,
-	.remove = gpd_fan_remove,
 	.driver = {
 		.name = KBUILD_MODNAME,
 	},
-- 
2.25.1