Re: [PATCH 11/16] iio: adc: at91-sama5d2_adc: add locking parameter to at91_adc_read_info_raw()

Claudiu.Beznea
2022-06-14T08:50:53Z

On 11.06.2022 20:58, Jonathan Cameron wrote:
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>
> On Thu, 9 Jun 2022 11:32:08 +0300
> Claudiu Beznea <claudiu.beznea@microchip.com> wrote:
>
>> Add a parameter to at91_adc_read_info_raw() to specify if st->lock mutex
>> need to be acquired. This prepares for the addition of temperature sensor
>> code which will re-use at91_adc_read_info_raw() function to read 2 voltages
>> for determining the real temperature.
>
> This looks like a potential lock dependency issue.
> iio_device_claim_direct_mode() takes an internal iio lock, and
> you then take st->lock.
>
> If you are going to invert that locking order in another path
> you have a deadlock.
>
> So rethink this. If you want to reuse the code you'll need to factor
> it out to a separate function that takes none of the locks then
> take all locks needed in each call path (in the same order).

OK, I'll check it.

>
> Jonathan
>
>
>>
>> Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
>> ---
>> drivers/iio/adc/at91-sama5d2_adc.c | 15 ++++++++++-----
>> 1 file changed, 10 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
>> index 1283bcf4e682..8f8fef42de84 100644
>> --- a/drivers/iio/adc/at91-sama5d2_adc.c
>> +++ b/drivers/iio/adc/at91-sama5d2_adc.c
>> @@ -1583,7 +1583,8 @@ static irqreturn_t at91_adc_interrupt(int irq, void *private)
>> }
>>
>> static int at91_adc_read_info_raw(struct iio_dev *indio_dev,
>> - struct iio_chan_spec const *chan, int *val)
>> + struct iio_chan_spec const *chan, int *val,
>> + bool lock)
>> {
>> struct at91_adc_state *st = iio_priv(indio_dev);
>> int (*fn)(struct at91_adc_state *, int, u16 *) = NULL;
>> @@ -1602,13 +1603,15 @@ static int at91_adc_read_info_raw(struct iio_dev *indio_dev,
>> ret = iio_device_claim_direct_mode(indio_dev);
>> if (ret)
>> return ret;
>> - mutex_lock(&st->lock);
>> + if (lock)
>> + mutex_lock(&st->lock);
>>
>> if (fn) {
>> ret = fn(st, chan->channel, &tmp_val);
>> *val = tmp_val;
>> ret = at91_adc_adjust_val_osr(st, val);
>> - mutex_unlock(&st->lock);
>> + if (lock)
>> + mutex_unlock(&st->lock);
>> iio_device_release_direct_mode(indio_dev);
>>
>> return ret;
>> @@ -1644,7 +1647,8 @@ static int at91_adc_read_info_raw(struct iio_dev *indio_dev,
>> /* Needed to ACK the DRDY interruption */
>> at91_adc_readl(st, LCDR);
>>
>> - mutex_unlock(&st->lock);
>> + if (lock)
>> + mutex_unlock(&st->lock);
>>
>> iio_device_release_direct_mode(indio_dev);
>> return ret;
>> @@ -1658,7 +1662,8 @@ static int at91_adc_read_raw(struct iio_dev *indio_dev,
>>
>> switch (mask) {
>> case IIO_CHAN_INFO_RAW:
>> - return at91_adc_read_info_raw(indio_dev, chan, val);
>> + return at91_adc_read_info_raw(indio_dev, chan, val, true);
>> +
>> case IIO_CHAN_INFO_SCALE:
>> *val = st->vref_uv / 1000;
>> if (chan->differential)
>