linux-kernel - Re: [PATCH] iio: cros_ec_accel_legacy: Always release lock when returning from

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Message-ID: <CAPUE2us7HZvSbpCddx4u_5KcdxedNd43-o=MZDiNfcpbzt9aXA@mail.gmail.com>
Date:   Mon, 15 Jul 2019 16:17:24 -0700
From:   Gwendal Grignou <gwendal@...omium.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Benson Leung <bleung@...gle.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Benson Leung <bleung@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Guenter Roeck <groeck@...omium.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH] iio: cros_ec_accel_legacy: Always release lock when
 returning from _read()

Sorry for the original mistake. I upload a patch at
https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/1702884.

On Mon, Jul 15, 2019 at 1:04 PM Matthias Kaehlcke <mka@...omium.org> wrote:
>
> Hi Benson,
>
> On Mon, Jul 15, 2019 at 12:55:57PM -0700, Benson Leung wrote:
> > Hi Matthias,
> >
> > On Mon, Jul 15, 2019 at 12:10:17PM -0700, Matthias Kaehlcke wrote:
> > > Before doing any actual work cros_ec_accel_legacy_read() acquires
> > > a mutex, which is released at the end of the function. However for
> > > 'calibbias' channels the function returns directly, without releasing
> > > the lock. The next attempt to acquire the lock blocks forever. Instead
> > > of an explicit return statement use the common return path, which
> > > releases the lock.
> > >
> > > Fixes: 11b86c7004ef1 ("platform/chrome: Add cros_ec_accel_legacy driver")
> > > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > > ---
> > >  drivers/iio/accel/cros_ec_accel_legacy.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iio/accel/cros_ec_accel_legacy.c b/drivers/iio/accel/cros_ec_accel_legacy.c
> > > index 46bb2e421bb9..27ca4a64dddf 100644
> > > --- a/drivers/iio/accel/cros_ec_accel_legacy.c
> > > +++ b/drivers/iio/accel/cros_ec_accel_legacy.c
> > > @@ -206,7 +206,8 @@ static int cros_ec_accel_legacy_read(struct iio_dev *indio_dev,
> > >     case IIO_CHAN_INFO_CALIBBIAS:
> > >             /* Calibration not supported. */
> > >             *val = 0;
> > > -           return IIO_VAL_INT;
> > > +           ret = IIO_VAL_INT;
> > > +           break;
> >
> > The value of ret is not used below this. It seems to be only used in
> > case IIO_CHAN_INFO_RAW. In fact, with your change,
> > there's no return value at all and we just reach the end of
> > cros_ec_accel_legacy_read.
> >
> > >     default:
> > >             return -EINVAL;
> > >     }
> >
>
> I messed up. I was over-confident that a FROMLIST patch in our 4.19
> kernel + this patch applying on upstream means that upstream uses the
> same code. I should have double-checked that the upstream context is
> actually the same.
>
> Sorry for the noise.