On Tue, Sep 29, 2020 at 7:15 PM Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > > On Mon, 28 Sep 2020 16:13:32 +0300 > Mircea Caprioru <mircea.caprioru@xxxxxxxxxx> wrote: > > > From: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx> > > > > As part of the general cleanup of indio_dev->mlock, this change replaces > > it with a local lock on the device's state structure. > > > > This is part of a bigger cleanup. > > Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@xxxxxxxxxxxxxx/ > > > > Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx> > > Signed-off-by: Mircea Caprioru <mircea.caprioru@xxxxxxxxxx> > > There are more problems in the locking in here than just this one. > See below. The taking of mlock like this was what originally motivated > the efforts to hide it away from drivers. > > In this particular case I don't think a local lock is the correct solution. > > Thanks, > > Jonathan > > > > --- > > drivers/iio/adc/vf610_adc.c | 28 ++++++++++++++++++++-------- > > 1 file changed, 20 insertions(+), 8 deletions(-) > > > > diff --git a/drivers/iio/adc/vf610_adc.c b/drivers/iio/adc/vf610_adc.c > > index 1d794cf3e3f1..b7d583993f0b 100644 > > --- a/drivers/iio/adc/vf610_adc.c > > +++ b/drivers/iio/adc/vf610_adc.c > > @@ -168,6 +168,15 @@ struct vf610_adc { > > > > struct completion completion; > > u16 buffer[8]; > > Side note. That buffer isn't correctly aligned. I'll add this one to > my next series fixing those. > > > + /* > > + * Lock to protect the device state during a potential concurrent > > + * read access from userspace. Reading a raw value requires a sequence > > + * of register writes, then a wait for a completion callback, > > + * and finally a register read, during which userspace could issue > > + * another read request. This lock protects a read access from > > + * ocurring before another one has finished. > > + */ > > + struct mutex lock; > > }; > > > > static const u32 vf610_hw_avgs[] = { 1, 4, 8, 16, 32 }; > > @@ -464,11 +473,11 @@ static int vf610_set_conversion_mode(struct iio_dev *indio_dev, > > { > > struct vf610_adc *info = iio_priv(indio_dev); > > > > - mutex_lock(&indio_dev->mlock); > > + mutex_lock(&info->lock); > Hmm. So there is a bit of a question on what the locking here is doing. > (see below for a different use of mlock). > > What it will do currently is to prevent the conversion mode changing whilst > we are in buffered mode. It will also protect against concurrent > calls of this function. > > I would replace this with iio_device_claim_direct_mode() rather than a > local lock. This raises a new question: if there's any drivers that we missed [for iio_device_claim_direct_mode()]. While I was aware of iio_device_claim_direct_mode(), I missed this fact when pushing the mlock cleanup. Oh well, I'll do a quick audit over the current drivers that were converted. Hopefully I don't find anything :P > > > info->adc_feature.conv_mode = mode; > > vf610_adc_calculate_rates(info); > > vf610_adc_hw_init(info); > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > > > return 0; > > } > > @@ -632,9 +641,9 @@ static int vf610_read_raw(struct iio_dev *indio_dev, > > switch (mask) { > > case IIO_CHAN_INFO_RAW: > > case IIO_CHAN_INFO_PROCESSED: > > - mutex_lock(&indio_dev->mlock); > > + mutex_lock(&info->lock); > > if (iio_buffer_enabled(indio_dev)) { > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > Should be use iio_device_claim_direct_mode() > > mlock is being taken here to stop us entering buffered mode. > > Whilst I'd rather a driver didn't rely on internal details of > IIO, it is rather fiddly to get the locking right when there is a completion > going on, so I think here you are safe to do so. > > > return -EBUSY; > > } > > > > @@ -645,11 +654,11 @@ static int vf610_read_raw(struct iio_dev *indio_dev, > > ret = wait_for_completion_interruptible_timeout > > (&info->completion, VF610_ADC_TIMEOUT); > > if (ret == 0) { > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > return -ETIMEDOUT; > > } > > if (ret < 0) { > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > return ret; > > } > > > > @@ -668,11 +677,11 @@ static int vf610_read_raw(struct iio_dev *indio_dev, > > > > break; > > default: > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > return -EINVAL; > > } > > > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > return IIO_VAL_INT; > > > > case IIO_CHAN_INFO_SCALE: > > @@ -807,6 +816,9 @@ static int vf610_adc_probe(struct platform_device *pdev) > > } > > > > info = iio_priv(indio_dev); > > + > > + mutex_init(&info->lock); > > + > > info->dev = &pdev->dev; > > > > info->regs = devm_platform_ioremap_resource(pdev, 0); >
