linux-kernel - Re: [PATCH v2 1/3] hwmon: tmp421: handle I2C errors

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Message-ID: <20210924022020.GA3032273@roeck-us.net>
Date:   Thu, 23 Sep 2021 19:20:20 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Paul Fertser <fercerpav@...il.com>
Cc:     linux-hwmon@...r.kernel.org, Jean Delvare <jdelvare@...e.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/3] hwmon: tmp421: handle I2C errors

On Thu, Sep 23, 2021 at 12:47:59PM +0300, Paul Fertser wrote:
> Function i2c_smbus_read_byte_data() can return a negative error number
> instead of the data read if I2C transaction failed for whatever reason.
> 
> I consider this fix to be stable material as lack of error checking here
> leads to serious issues on production hardware. Errors treated as
> temperatures produce spurious critical temperature-crossed-threshold
> errors in BMC logs for OCP server hardware. The patch was tested with
> Mellanox OCP Mezzanine card emulating TMP421 protocol for temperature
> sensing which sometimes leads to I2C protocol error during early boot up
> stage.

Possibly, but this doesn't belong into the commit log but after --- as
written. I'd suggest to leave the "I consider this fix to be stable
material" off, rephrase to "Lack of error checking can lead to serious..."
which does belong in the commit description, and add a Fixes: tag which
marks the patch for stable releases. Also, drop the char -> bool change
from the bug fix; it is unrelated and should be a separate cleanup patch.

> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Paul Fertser <fercerpav@...il.com>
> ---
> 
> Changes from v1:
>  - Reorganise code following excellent suggestion by Guenter Roeck
>    to use tagged errors consistently
> 
>  drivers/hwmon/tmp421.c | 45 +++++++++++++++++++++++++++++++-----------
>  1 file changed, 33 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/hwmon/tmp421.c b/drivers/hwmon/tmp421.c
> index ede66ea6a730..63cb6badb478 100644
> --- a/drivers/hwmon/tmp421.c
> +++ b/drivers/hwmon/tmp421.c
> @@ -93,7 +93,7 @@ struct tmp421_data {
>  	struct hwmon_channel_info temp_info;
>  	const struct hwmon_channel_info *info[2];
>  	struct hwmon_chip_info chip;
> -	char valid;
> +	bool valid;

This is a cleanup, not a bug fix, and it isn't even mentioned
in the patch description.

>  	unsigned long last_updated;
>  	unsigned long channels;
>  	u8 config;
> @@ -119,38 +119,59 @@ static int temp_from_u16(u16 reg)
>  	return (temp * 1000 + 128) / 256;
>  }
>  
> -static struct tmp421_data *tmp421_update_device(struct device *dev)
> +static int tmp421_update_device(struct tmp421_data *data)
>  {
> -	struct tmp421_data *data = dev_get_drvdata(dev);
>  	struct i2c_client *client = data->client;
> +	int ret = 0;
>  	int i;
>  
>  	mutex_lock(&data->update_lock);
>  
>  	if (time_after(jiffies, data->last_updated + (HZ / 2)) ||
>  	    !data->valid) {
> -		data->config = i2c_smbus_read_byte_data(client,
> -			TMP421_CONFIG_REG_1);
> +		ret = i2c_smbus_read_byte_data(client,
> +					       TMP421_CONFIG_REG_1);
> +		if (ret < 0)
> +			goto exit;
> +		data->config = ret;
>  
>  		for (i = 0; i < data->channels; i++) {
> -			data->temp[i] = i2c_smbus_read_byte_data(client,
> -				TMP421_TEMP_MSB[i]) << 8;
> -			data->temp[i] |= i2c_smbus_read_byte_data(client,
> -				TMP421_TEMP_LSB[i]);
> +			ret = i2c_smbus_read_byte_data(client,
> +						       TMP421_TEMP_MSB[i]);
> +			if (ret < 0)
> +				goto exit;
> +			data->temp[i] = ret << 8;
> +
> +			ret = i2c_smbus_read_byte_data(client,
> +						       TMP421_TEMP_LSB[i]);
> +			if (ret < 0)
> +				goto exit;
> +			data->temp[i] |= ret;
>  		}
>  		data->last_updated = jiffies;
> -		data->valid = 1;
> +		data->valid = true;
>  	}
>  
> +exit:
>  	mutex_unlock(&data->update_lock);
>  
> -	return data;
> +	if (ret < 0) {
> +		data->valid = false;
> +		return ret;
> +	}
> +
> +	return 0;
>  }
>  
>  static int tmp421_read(struct device *dev, enum hwmon_sensor_types type,
>  		       u32 attr, int channel, long *val)
>  {
> -	struct tmp421_data *tmp421 = tmp421_update_device(dev);
> +	struct tmp421_data *tmp421 = dev_get_drvdata(dev);
> +	int ret = 0;
> +
> +	ret = tmp421_update_device(tmp421);
> +	if (ret)
> +		return ret;
>  
>  	switch (attr) {
>  	case hwmon_temp_input: