linux-kernel - Re: [PATCH v3] iio: adc: exynos: do not rely on 'users' counter in ISR

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Date:   Sat, 10 Oct 2020 17:50:57 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     dmitry.torokhov@...il.com
Cc:     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>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        linux-iio@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] iio: adc: exynos: do not rely on 'users' counter in
 ISR

On Tue, 6 Oct 2020 14:55:09 -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.
> 
> Reported-by: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
> Acked-by: Krzysztof Kozlowski <krzk@...nel.org>
> Reviewed-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
Applied to the togreg branch of iio.git and pushed out as testing
for the autobuilders to work their magic.

Given this doesn't have a fixes tag etc I'm assuming it isn't
high priority etc.  Let me know if it is!

Thanks,

Jonathan
> ---
> 
> v3: fixed typo in exynos_adc_ts_close() per Michał Mirosław
> v2: switched from ordinary read/write to READ_ONCE/WRITE_ONCE per Michał
> Mirosław
> 
>  drivers/iio/adc/exynos_adc.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/exynos_adc.c b/drivers/iio/adc/exynos_adc.c
> index 22131a677445..908df4b9b93c 100644
> --- a/drivers/iio/adc/exynos_adc.c
> +++ b/drivers/iio/adc/exynos_adc.c
> @@ -7,6 +7,7 @@
>   *  Copyright (C) 2013 Naveen Krishna Chatradhi <ch.naveen@...sung.com>
>   */
>  
> +#include <linux/compiler.h>
>  #include <linux/module.h>
>  #include <linux/platform_device.h>
>  #include <linux/interrupt.h>
> @@ -135,6 +136,8 @@ struct exynos_adc {
>  	u32			value;
>  	unsigned int            version;
>  
> +	bool			ts_enabled;
> +
>  	bool			read_ts;
>  	u32			ts_x;
>  	u32			ts_y;
> @@ -633,7 +636,7 @@ static irqreturn_t exynos_ts_isr(int irq, void *dev_id)
>  	bool pressed;
>  	int ret;
>  
> -	while (info->input->users) {
> +	while (READ_ONCE(info->ts_enabled)) {
>  		ret = exynos_read_s3c64xx_ts(dev, &x, &y);
>  		if (ret == -ETIMEDOUT)
>  			break;
> @@ -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, false);
>  	disable_irq(info->tsirq);
>  }
>