Re: [PATCH v2] drivers/hwmon/adm9240: fix data race in adm9240_fan_read

[Guenter Roeck <linux@xxxxxxxxxxxx>]

On 9/22/22 16:43, Li Zhong wrote:
> In
> adm9240_read()
>    adm9240_fan_read()
>      adm9240_write_fan_div(),
>
> it assumes that the caller of adm9240_write_fan_div() must hold
> data->update_lock. Otherwise, it may cause data races when data is
> updated by other threads.
>
> Signed-off-by: Li Zhong <floridsleeves@xxxxxxxxx>
> ---
> v2: add mutex_unlock() in error handling
>
>   drivers/hwmon/adm9240.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hwmon/adm9240.c b/drivers/hwmon/adm9240.c
> index 483cd757abd3..d58999e186dc 100644
> --- a/drivers/hwmon/adm9240.c
> +++ b/drivers/hwmon/adm9240.c
> @@ -501,16 +501,22 @@ static int adm9240_fan_read(struct device *dev, u32 attr, int channel, long *val
>   
>   	switch (attr) {
>   	case hwmon_fan_input:
> +		mutex_lock(&data->update_lock);
>   		err = regmap_read(data->regmap, ADM9240_REG_FAN(channel), &regval);
> -		if (err < 0)
> +		if (err < 0) {
> +			mutex_unlock(&data->update_lock);
>   			return err;
> +		}
>   		if (regval == 255 && data->fan_div[channel] < 3) {
>   			/* adjust fan clock divider on overflow */
>   			err = adm9240_write_fan_div(data, channel,
>   						    ++data->fan_div[channel]);
> -			if (err)
> +			if (err) {
> +				mutex_unlock(&data->update_lock);
>   				return err;
> +			}
>   		}
> +		mutex_unlock(&data->update_lock);
>   		*val = FAN_FROM_REG(regval, BIT(data->fan_div[channel]));

Unfortunately, this is still racy. All accesses to data->fan_div[channel]
need to be included in the lock.

Thanks,
Guenter

>   		break;
>   	case hwmon_fan_div: