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

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Message-ID: <20190715200447.GT250418@google.com>
Date:   Mon, 15 Jul 2019 13:04:47 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Benson Leung <bleung@...gle.com>
Cc:     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@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Gwendal Grignou <gwendal@...omium.org>,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH] iio: cros_ec_accel_legacy: Always release lock when
 returning from _read()

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.