[PATCH 3.2 038/131] hwmon: (amc6821) Fix possible race condition bug

[Ben Hutchings]

3.2.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Axel Lin <axel.lin@xxxxxxxxxx>

commit cf44819c98db11163f58f08b822d626c7a8f5188 upstream.

Ensure mutex lock protects the read-modify-write period to prevent possible
race condition bug.
In additional, update data->valid should also be protected by the mutex lock.

Signed-off-by: Axel Lin <axel.lin@xxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/hwmon/amc6821.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

--- a/drivers/hwmon/amc6821.c
+++ b/drivers/hwmon/amc6821.c
@@ -360,11 +360,13 @@ static ssize_t set_pwm1_enable(
 	if (config)
 		return config;
 
+	mutex_lock(&data->update_lock);
 	config = i2c_smbus_read_byte_data(client, AMC6821_REG_CONF1);
 	if (config < 0) {
 			dev_err(&client->dev,
 			"Error reading configuration register, aborting.\n");
-			return config;
+			count = config;
+			goto unlock;
 	}
 
 	switch (val) {
@@ -381,14 +383,15 @@ static ssize_t set_pwm1_enable(
 		config |= AMC6821_CONF1_FDRC1;
 		break;
 	default:
-		return -EINVAL;
+		count = -EINVAL;
+		goto unlock;
 	}
-	mutex_lock(&data->update_lock);
 	if (i2c_smbus_write_byte_data(client, AMC6821_REG_CONF1, config)) {
 			dev_err(&client->dev,
 			"Configuration register write error, aborting.\n");
 			count = -EIO;
 	}
+unlock:
 	mutex_unlock(&data->update_lock);
 	return count;
 }
@@ -495,8 +498,9 @@ static ssize_t set_temp_auto_point_temp(
 		return -EINVAL;
 	}
 
-	data->valid = 0;
 	mutex_lock(&data->update_lock);
+	data->valid = 0;
+
 	switch (ix) {
 	case 0:
 		ptemp[0] = SENSORS_LIMIT(val / 1000, 0,
@@ -669,13 +673,14 @@ static ssize_t set_fan1_div(
 	if (config)
 		return config;
 
+	mutex_lock(&data->update_lock);
 	config = i2c_smbus_read_byte_data(client, AMC6821_REG_CONF4);
 	if (config < 0) {
 		dev_err(&client->dev,
 			"Error reading configuration register, aborting.\n");
-		return config;
+		count = config;
+		goto EXIT;
 	}
-	mutex_lock(&data->update_lock);
 	switch (val) {
 	case 2:
 		config &= ~AMC6821_CONF4_PSPR;

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