On Mon, 18 Oct 2021 13:37:31 +0200
Noralf Trønnes <noralf@xxxxxxxxxxx> wrote:
> When reading the voltage:
>
> $ cat /sys/bus/iio/devices/iio\:device0/in_voltage0_raw
>
> Lockdep complains:
>
> [ 153.910616] ======================================================
> [ 153.916918] WARNING: possible circular locking dependency detected
> [ 153.923221] 5.14.0+ #5 Not tainted
> [ 153.926692] ------------------------------------------------------
> [ 153.932992] cat/717 is trying to acquire lock:
> [ 153.937525] c2585358 (&indio_dev->mlock){+.+.}-{3:3}, at: iio_device_claim_direct_mode+0x28/0x44
> [ 153.946541]
> but task is already holding lock:
> [ 153.952487] c2585860 (&dln2->mutex){+.+.}-{3:3}, at: dln2_adc_read_raw+0x94/0x2bc [dln2_adc]
> [ 153.961152]
> which lock already depends on the new lock.
>
> Fix this by not calling into the iio core underneath the dln2->mutex lock.
>
> Fixes: 7c0299e879dd ("iio: adc: Add support for DLN2 ADC")
> Cc: Jack Andersen <jackoalan@xxxxxxxxx>
> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
Applied to the fixes-togreg branch of iio.git and marked for stable.
Thanks,
Jonathan
> ---
>
> Note that this patch is needed for the driver to be usable:
>
> mfd: dln2: Add cell for initializing DLN2 ADC
> https://lore.kernel.org/lkml/20211018112541.25466-1-noralf@xxxxxxxxxxx/T/#u
>
>
> drivers/iio/adc/dln2-adc.c | 15 +++++++--------
> 1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/iio/adc/dln2-adc.c b/drivers/iio/adc/dln2-adc.c
> index 16407664182c..6c67192946aa 100644
> --- a/drivers/iio/adc/dln2-adc.c
> +++ b/drivers/iio/adc/dln2-adc.c
> @@ -248,7 +248,6 @@ static int dln2_adc_set_chan_period(struct dln2_adc *dln2,
> static int dln2_adc_read(struct dln2_adc *dln2, unsigned int channel)
> {
> int ret, i;
> - struct iio_dev *indio_dev = platform_get_drvdata(dln2->pdev);
> u16 conflict;
> __le16 value;
> int olen = sizeof(value);
> @@ -257,13 +256,9 @@ static int dln2_adc_read(struct dln2_adc *dln2, unsigned int channel)
> .chan = channel,
> };
>
> - ret = iio_device_claim_direct_mode(indio_dev);
> - if (ret < 0)
> - return ret;
> -
> ret = dln2_adc_set_chan_enabled(dln2, channel, true);
> if (ret < 0)
> - goto release_direct;
> + return ret;
>
> ret = dln2_adc_set_port_enabled(dln2, true, &conflict);
> if (ret < 0) {
> @@ -300,8 +295,6 @@ static int dln2_adc_read(struct dln2_adc *dln2, unsigned int channel)
> dln2_adc_set_port_enabled(dln2, false, NULL);
> disable_chan:
> dln2_adc_set_chan_enabled(dln2, channel, false);
> -release_direct:
> - iio_device_release_direct_mode(indio_dev);
>
> return ret;
> }
> @@ -337,10 +330,16 @@ static int dln2_adc_read_raw(struct iio_dev *indio_dev,
>
> switch (mask) {
> case IIO_CHAN_INFO_RAW:
> + ret = iio_device_claim_direct_mode(indio_dev);
> + if (ret < 0)
> + return ret;
> +
> mutex_lock(&dln2->mutex);
> ret = dln2_adc_read(dln2, chan->channel);
> mutex_unlock(&dln2->mutex);
>
> + iio_device_release_direct_mode(indio_dev);
> +
> if (ret < 0)
> return ret;
>
