Re: [PATCH v2] staging: iio: adc: ad7816: Protect sysfs attributes with mutex

[Jonathan Cameron]

On Sun, 20 Sep 2026 12:15:22 +0300
Abdelnasser Hussein <abdelnasserhussein11@xxxxxxxxx> wrote:

> The sysfs store functions (ad7816_store_mode and ad7816_store_channel)
> modify the device state and toggle GPIO pins. If accessed concurrently
> by userspace during an ongoing SPI transfer, this could corrupt the
> SPI transaction.

See below. One of them doesn't seem to have that possible affect.

Thanks,

Jonathan

> 
> Add the existing chip->lock guard to these functions to serialize
> access and prevent race conditions.
> 
> Fixes: 7924425db04a ("staging: iio: adc: new driver for AD7816 devices")
> Suggested-by: Joshua Crofts <joshua.crofts1@xxxxxxxxx>
> Reviewed-by: Joshua Crofts <joshua.crofts1@xxxxxxxxx>
> Signed-off-by: Abdelnasser Hussein <abdelnasserhussein11@xxxxxxxxx>
> ---
> Changes in v2:
> - Added a blank line after guard(mutex) statements as requested by Joshua.
> - Added Fixes tag as requested by Dan.
> - Collected Reviewed-by tag from Joshua.
> 
>  drivers/staging/iio/adc/ad7816.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/staging/iio/adc/ad7816.c b/drivers/staging/iio/adc/ad7816.c
> index f76f0215119a..2a15d7598abb 100644
> --- a/drivers/staging/iio/adc/ad7816.c
> +++ b/drivers/staging/iio/adc/ad7816.c
> @@ -143,6 +143,8 @@ static ssize_t ad7816_store_mode(struct device *dev,
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct ad7816_chip_info *chip = iio_priv(indio_dev);
>  
> +	guard(mutex)(&chip->lock);
> +
>  	if (strcmp(buf, "full") == 0) {
>  		gpiod_set_value(chip->rdwr_pin, 1);
>  		chip->mode = AD7816_FULL;
> @@ -207,6 +209,8 @@ static ssize_t ad7816_store_channel(struct device *dev,
>  		return -EINVAL;
>  	}
>  
> +	guard(mutex)(&chip->lock);
This isn't toggling pins or modifying anything on the device state side
of things. So at very least the commit message needs to be expanded to
what this is doing that needs a lock.

> +
>  	chip->channel_id = data;
>  
>  	return len;