[PATCH] staging: iio: ad5933: avoid uninitialized variable in error case

[PATCH] staging: iio: ad5933: avoid uninitialized variable in error case

[Arnd Bergmann]

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.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/staging/iio/impedance-analyzer/ad5933.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/iio/impedance-analyzer/ad5933.c b/drivers/staging/iio/impedance-analyzer/ad5933.c
index 10c43dda0f5a..304bb464e478 100644
--- a/drivers/staging/iio/impedance-analyzer/ad5933.c
+++ b/drivers/staging/iio/impedance-analyzer/ad5933.c
@@ -647,6 +647,7 @@ 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) {
@@ -658,9 +659,9 @@ static void ad5933_work(struct work_struct *work)
 		return;
 	}
 
-	ad5933_i2c_read(st->client, AD5933_REG_STATUS, 1, &status);
+	ret = ad5933_i2c_read(st->client, AD5933_REG_STATUS, 1, &status);
 
-	if (status & AD5933_STAT_DATA_VALID) {
+	if (!ret && (status & AD5933_STAT_DATA_VALID)) {
 		int scan_count = bitmap_weight(indio_dev->active_scan_mask,
 					       indio_dev->masklength);
 		ad5933_i2c_read(st->client,
-- 
2.7.0

Re: [PATCH] staging: iio: ad5933: avoid uninitialized variable in error case

[Jonathan Cameron]

On 25/01/16 15:50, 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.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Hi Arnd,

Thanks for the patch.   The handling in here is a little fiddly
by the look of things. Lars can you take a look at this when
you have a minute?

At a very high level, it doesn't make sense to fix this instance and
not the one in the context of the patch below.
See below...
> ---
>  drivers/staging/iio/impedance-analyzer/ad5933.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/iio/impedance-analyzer/ad5933.c b/drivers/staging/iio/impedance-analyzer/ad5933.c
> index 10c43dda0f5a..304bb464e478 100644
> --- a/drivers/staging/iio/impedance-analyzer/ad5933.c
> +++ b/drivers/staging/iio/impedance-analyzer/ad5933.c
> @@ -647,6 +647,7 @@ 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) {
> @@ -658,9 +659,9 @@ static void ad5933_work(struct work_struct *work)
>  		return;
>  	}
>  
> -	ad5933_i2c_read(st->client, AD5933_REG_STATUS, 1, &status);
> +	ret = ad5933_i2c_read(st->client, AD5933_REG_STATUS, 1, &status);
>  
> -	if (status & AD5933_STAT_DATA_VALID) {
> +	if (!ret && (status & AD5933_STAT_DATA_VALID)) {
The else is non trivial here as it assumes we will get the data later. If we
get such a failure, we probably want to drop out completely rather than paper
over the gaps..
>  		int scan_count = bitmap_weight(indio_dev->active_scan_mask,
>  					       indio_dev->masklength);
Same issue on the next line - this results in known garbage data being spooled
out.
>  		ad5933_i2c_read(st->client,
> 

Re: [PATCH] staging: iio: ad5933: avoid uninitialized variable in error case

[Lars-Peter Clausen]

On 01/30/2016 03:18 PM, Jonathan Cameron wrote:
> On 25/01/16 15:50, 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.
>>
>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Hi Arnd,
> 
> Thanks for the patch.   The handling in here is a little fiddly
> by the look of things. Lars can you take a look at this when
> you have a minute?
> 
> At a very high level, it doesn't make sense to fix this instance and
> not the one in the context of the patch below.
> See below...
>> ---
>>  drivers/staging/iio/impedance-analyzer/ad5933.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/iio/impedance-analyzer/ad5933.c b/drivers/staging/iio/impedance-analyzer/ad5933.c
>> index 10c43dda0f5a..304bb464e478 100644
>> --- a/drivers/staging/iio/impedance-analyzer/ad5933.c
>> +++ b/drivers/staging/iio/impedance-analyzer/ad5933.c
>> @@ -647,6 +647,7 @@ 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) {
>> @@ -658,9 +659,9 @@ static void ad5933_work(struct work_struct *work)
>>  		return;
>>  	}
>>  
>> -	ad5933_i2c_read(st->client, AD5933_REG_STATUS, 1, &status);
>> +	ret = ad5933_i2c_read(st->client, AD5933_REG_STATUS, 1, &status);
>>  
>> -	if (status & AD5933_STAT_DATA_VALID) {
>> +	if (!ret && (status & AD5933_STAT_DATA_VALID)) {
> The else is non trivial here as it assumes we will get the data later. If we
> get such a failure, we probably want to drop out completely rather than paper
> over the gaps..

I agree. Although we could argue that Arnd's approach allows to recover from
temporary failure. But then again we don't want to keep polling forever if
it's a permanent failure. I'd say the best thing for a quick fix is to just
error out and assume the error is permanent.

>>  		int scan_count = bitmap_weight(indio_dev->active_scan_mask,
>>  					       indio_dev->masklength);
> Same issue on the next line - this results in known garbage data being spooled
> out.

Also agreed.