Re: [PATCH] iio: imu: st_lsm6dsx: fix possible lockup during FIFO read

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> Prevent st_lsm6dsx_read_fifo and st_lsm6dsx_read_tagged_fifo functions
> from falling in an infinite loop in case pattern_len is equal to zero and
> the device FIFO is not empty.
> 
> Signed-off-by: Silvano Seva <s.seva@4sigma.it>
> ---
>  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> index 0a7cd8c1aa33..7f343614f8a5 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> @@ -395,12 +395,17 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
>  	fifo_len = (le16_to_cpu(fifo_status) & fifo_diff_mask) *
>  		   ST_LSM6DSX_CHAN_SIZE;
>  	fifo_len = (fifo_len / pattern_len) * pattern_len;
> +	if (!fifo_len)
> +		return 0;

I do not think this check is necessary since if fifo_len is 0 we will not run
the for loop, right?

>  
>  	acc_sensor = iio_priv(hw->iio_devs[ST_LSM6DSX_ID_ACC]);
>  	gyro_sensor = iio_priv(hw->iio_devs[ST_LSM6DSX_ID_GYRO]);
>  	if (hw->iio_devs[ST_LSM6DSX_ID_EXT0])
>  		ext_sensor = iio_priv(hw->iio_devs[ST_LSM6DSX_ID_EXT0]);
>  
> +	if (!pattern_len)
> +		pattern_len = ST_LSM6DSX_SAMPLE_SIZE;

same here, I do not think pattern_len can be 0 since hw->sip must be greater
than 0 in order to enable the FIFO. Moreover, this check should be some lines
above since we have already divided fifo_len by pattern_len here.

> +
>  	for (read_len = 0; read_len < fifo_len; read_len += pattern_len) {
>  		err = st_lsm6dsx_read_block(hw, ST_LSM6DSX_REG_FIFO_OUTL_ADDR,
>  					    hw->buff, pattern_len,
> @@ -623,6 +628,9 @@ int st_lsm6dsx_read_tagged_fifo(struct st_lsm6dsx_hw *hw)
>  	if (!fifo_len)
>  		return 0;
>  
> +	if (!pattern_len)
> +		pattern_len = ST_LSM6DSX_TAGGED_SAMPLE_SIZE;

for the reason above, this is not necessary.

Regards,
Lorenzo

> +
>  	for (read_len = 0; read_len < fifo_len; read_len += pattern_len) {
>  		err = st_lsm6dsx_read_block(hw,
>  					    ST_LSM6DSX_REG_FIFO_OUT_TAG_ADDR,
> -- 
> 2.48.1
> 

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