Re: [PATCH v2 1/2] gpio: shared-proxy: Fix race between concurrent first users

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] gpio: shared: set_value(0) is a no-op on ASIS lines driven HIGH
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commit b2e913f9e7adbb02eb24728f50149f4b95e20857
Author: Shawn Guo <shengchao.guo@oss.qualcomm.com>

gpio: shared-proxy: Fix race between concurrent first users

This commit fixes a race condition where multiple consumers probing concurrently
can both request a shared GPIO before either configures it, causing both to fail.
It tracks the number of proxies that have actually configured the line, allowing
initialization only when no other proxy has done so.

> diff --git a/drivers/gpio/gpio-shared-proxy.c b/drivers/gpio/gpio-shared-proxy.c
> index bc69b8729d196..0d1d724a6a376 100644
> --- a/drivers/gpio/gpio-shared-proxy.c
> +++ b/drivers/gpio/gpio-shared-proxy.c

[ ... ]

> @@ -230,10 +275,21 @@ static int gpio_shared_proxy_set_cansleep(struct gpio_chip *gc,
>  					  unsigned int offset, int value)
>  {
>  	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
> +	int ret;
>  
>  	guard(mutex)(&proxy->shared_desc->mutex);
>  
> -	return gpio_shared_proxy_set_unlocked(proxy, value);
> +	/*
> +	 * A GPIOD_ASIS consumer may vote without ever setting the direction;
> +	 * count it as configured so a later user can't reset its vote.
> +	 */
> +	ret = gpio_shared_proxy_set_unlocked(proxy, value);

[Severity: Medium]
If a consumer requests a shared GPIO with GPIOD_ASIS and the physical line
is already driven HIGH, does shared_desc->def_val still default to 0?

When the consumer later calls gpiod_set_value(0) to drive the line LOW,
gpio_shared_proxy_set_unlocked() checks if value != shared_desc->def_val.
Since both value and def_val are 0, it skips calling
gpiod_set_value_cansleep() and returns success without changing the
hardware state.

Does this result in set_value(0) acting as a no-op on ASIS lines that are
initially driven HIGH?

> +	if (ret)
> +		return ret;
> +
> +	gpio_shared_proxy_mark_configured(proxy);
> +
> +	return 0;
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261016144919.1362846-1-shengchao.guo@oss.qualcomm.com?part=1