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    SubjectRe: [PATCH 10/16] iio: adc: max1027: Prevent single channel accesses during buffer reads
    On Fri, 20 Aug 2021 07:30:07 +0000
    "Sa, Nuno" <Nuno.Sa@analog.com> wrote:

    > > -----Original Message-----
    > > From: Sa, Nuno <Nuno.Sa@analog.com>
    > > Sent: Friday, August 20, 2021 9:21 AM
    > > To: Miquel Raynal <miquel.raynal@bootlin.com>; Jonathan Cameron
    > > <jic23@kernel.org>; Lars-Peter Clausen <lars@metafoo.de>
    > > Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>; linux-
    > > iio@vger.kernel.org; linux-kernel@vger.kernel.org
    > > Subject: RE: [PATCH 10/16] iio: adc: max1027: Prevent single channel
    > > accesses during buffer reads
    > >
    > > [External]
    > >
    > >
    > >
    > > > -----Original Message-----
    > > > From: Miquel Raynal <miquel.raynal@bootlin.com>
    > > > Sent: Wednesday, August 18, 2021 1:12 PM
    > > > To: Jonathan Cameron <jic23@kernel.org>; Lars-Peter Clausen
    > > > <lars@metafoo.de>
    > > > Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>; linux-
    > > > iio@vger.kernel.org; linux-kernel@vger.kernel.org; Miquel Raynal
    > > > <miquel.raynal@bootlin.com>
    > > > Subject: [PATCH 10/16] iio: adc: max1027: Prevent single channel
    > > > accesses during buffer reads
    > > >
    > > > [External]
    > > >
    > > > When hardware buffers are enabled (the cnvst pin being the
    > > trigger),
    > > > one
    > > > should not mess with the device state by requesting a single channel
    > > > read. Prevent it with a iio_buffer_enabled() check.
    > > >
    > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
    > > > ---
    > > > drivers/iio/adc/max1027.c | 2 ++
    > > > 1 file changed, 2 insertions(+)
    > > >
    > > > diff --git a/drivers/iio/adc/max1027.c b/drivers/iio/adc/max1027.c
    > > > index 223c9e4abd86..83526f3d7d3a 100644
    > > > --- a/drivers/iio/adc/max1027.c
    > > > +++ b/drivers/iio/adc/max1027.c
    > > > @@ -335,6 +335,8 @@ static int max1027_read_raw(struct iio_dev
    > > > *indio_dev,
    > > >
    > > > switch (mask) {
    > > > case IIO_CHAN_INFO_RAW:
    > > > + if (iio_buffer_enabled(indio_dev))
    > > > + return -EBUSY;
    > >
    > > I guess 'iio_device_claim_direct_mode()' would be a better option
    > > here? There's nothing preventing this check to pass and then,
    > > concurrently
    > > someone enables the buffer...
    > >
    >
    > Taking a second look, it seems that this check is already done [1]? Am I missing
    > I missing something?
    >
    > Also, I think we are returning with the 'st->lock' held...
    >
    > [1]: https://elixir.bootlin.com/linux/latest/source/drivers/iio/adc/max1027.c#L247
    Absolutely agree this should be done with iio_device_claim_direct_mode() to close the
    possible races.

    I wonder why this one has been missed in all the cleanups of that stuff? Looks like
    a simple case, but I guess it wasn't immediately visible in the read_raw() function
    so no one noticed.

    Jonathan

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