linux-kernel - Re: [PATCH] [v2] staging: iio: ad5933: avoid uninitialized variable in error case

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Date:   Tue, 25 Oct 2016 17:57:15 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Alison Schofield <amsfield22@...il.com>,
        linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v2] staging: iio: ad5933: avoid uninitialized variable
 in error case

On 24/10/16 16:22, Arnd Bergmann wrote:
> The ad5933_i2c_read function returns an error code to indicate
> whether it could read data or not. However ad5933_work() ignores
> this return code and just accesses the data unconditionally,
> which gets detected by gcc as a possible bug:
> 
> drivers/staging/iio/impedance-analyzer/ad5933.c: In function 'ad5933_work':
> drivers/staging/iio/impedance-analyzer/ad5933.c:649:16: warning: 'status' may be used uninitialized in this function [-Wmaybe-uninitialized]
> 
> This adds minimal error handling so we only evaluate the
> data if it was correctly read.
> 
> Link: https://patchwork.kernel.org/patch/8110281/
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
Looks good to me.

Lars?


> ---
> v2: handle failure for both affected reads instead of just the one
>     we get a warning for
> v2: do not retry on failure to avoid looping in case of permanent
>     errors
> ---
>  drivers/staging/iio/impedance-analyzer/ad5933.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/staging/iio/impedance-analyzer/ad5933.c b/drivers/staging/iio/impedance-analyzer/ad5933.c
> index 5eecf1cb1028..3892a7470410 100644
> --- a/drivers/staging/iio/impedance-analyzer/ad5933.c
> +++ b/drivers/staging/iio/impedance-analyzer/ad5933.c
> @@ -655,6 +655,7 @@ static void ad5933_work(struct work_struct *work)
>  	__be16 buf[2];
>  	int val[2];
>  	unsigned char status;
> +	int ret;
>  
>  	mutex_lock(&indio_dev->mlock);
>  	if (st->state == AD5933_CTRL_INIT_START_FREQ) {
> @@ -662,19 +663,22 @@ static void ad5933_work(struct work_struct *work)
>  		ad5933_cmd(st, AD5933_CTRL_START_SWEEP);
>  		st->state = AD5933_CTRL_START_SWEEP;
>  		schedule_delayed_work(&st->work, st->poll_time_jiffies);
> -		mutex_unlock(&indio_dev->mlock);
> -		return;
> +		goto out;
>  	}
>  
> -	ad5933_i2c_read(st->client, AD5933_REG_STATUS, 1, &status);
> +	ret = ad5933_i2c_read(st->client, AD5933_REG_STATUS, 1, &status);
> +	if (ret)
> +		goto out;
>  
>  	if (status & AD5933_STAT_DATA_VALID) {
>  		int scan_count = bitmap_weight(indio_dev->active_scan_mask,
>  					       indio_dev->masklength);
> -		ad5933_i2c_read(st->client,
> +		ret = ad5933_i2c_read(st->client,
>  				test_bit(1, indio_dev->active_scan_mask) ?
>  				AD5933_REG_REAL_DATA : AD5933_REG_IMAG_DATA,
>  				scan_count * 2, (u8 *)buf);
> +		if (ret)
> +			goto out;
>  
>  		if (scan_count == 2) {
>  			val[0] = be16_to_cpu(buf[0]);
> @@ -686,8 +690,7 @@ static void ad5933_work(struct work_struct *work)
>  	} else {
>  		/* no data available - try again later */
>  		schedule_delayed_work(&st->work, st->poll_time_jiffies);
> -		mutex_unlock(&indio_dev->mlock);
> -		return;
> +		goto out;
>  	}
>  
>  	if (status & AD5933_STAT_SWEEP_DONE) {
> @@ -700,7 +703,7 @@ static void ad5933_work(struct work_struct *work)
>  		ad5933_cmd(st, AD5933_CTRL_INC_FREQ);
>  		schedule_delayed_work(&st->work, st->poll_time_jiffies);
>  	}
> -
> +out:
>  	mutex_unlock(&indio_dev->mlock);
>  }
>  
>