linux-kernel - Re: [PATCH v2] iio: adc: exynos: do not rely on 'users' counter in ISR

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Message-ID: <20201006215051.GO1009802@dtor-ws>
Date:   Tue, 6 Oct 2020 14:50:51 -0700
From:   dmitry.torokhov@...il.com
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        linux-iio@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iio: adc: exynos: do not rely on 'users' counter in
 ISR

On Tue, Oct 06, 2020 at 09:39:07PM +0200, Michał Mirosław wrote:
> On Mon, Oct 05, 2020 at 09:12:14PM -0700, dmitry.torokhov@...il.com wrote:
> > The order in which 'users' counter is decremented vs calling drivers'
> > close() method is implementation specific, and we should not rely on
> > it. Let's introduce driver private flag and use it to signal ISR
> > to exit when device is being closed.
> > 
> > This has a side-effect of fixing issue of accessing inut->users
> > outside of input->mutex protection.
> [...]
> 
> Reviewed-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> (after with a fix mentioned below)
> 
> > --- a/drivers/iio/adc/exynos_adc.c
> > +++ b/drivers/iio/adc/exynos_adc.c
> [...]
> > @@ -712,6 +715,7 @@ static int exynos_adc_ts_open(struct input_dev *dev)
> >  {
> >  	struct exynos_adc *info = input_get_drvdata(dev);
> >  
> > +	WRITE_ONCE(info->ts_enabled, true);
> >  	enable_irq(info->tsirq);
> >  
> >  	return 0;
> > @@ -721,6 +725,7 @@ static void exynos_adc_ts_close(struct input_dev *dev)
> >  {
> >  	struct exynos_adc *info = input_get_drvdata(dev);
> >  
> > +	WRITE_ONCE(info->ts_enabled, true);
> >  	disable_irq(info->tsirq);
> 
> Shouldn't 'true' be 'false' here?

I swear if we disable cut-n-paste functionality there will be markable
reduction in bug rates...

Thanks for noticing this!

-- 
Dmitry