Re: [PATCH 22/23] gpiolib: Leverage revocable for other independent lifecycle instances

[Johan Hovold <johan@kernel.org>]

On Fri, Jan 16, 2026 at 08:10:35AM +0000, Tzung-Bi Shih wrote:
> There are independent lifecycle instances (e.g., other drivers) can save
> a raw pointer to the struct gpio_device (e.g., via gpio_device_find())
> or struct gpio_desc (e.g., via gpio_to_desc()).  In some operations,
> they have to access the underlying struct gpio_chip.
> 
> Leverage revocable for them so that they don't need to handle the
> synchronization by accessing the SRCU explicitly.
> 
> Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

>  static int gpiod_get_raw_value_commit(const struct gpio_desc *desc)
>  {
> -	struct gpio_device *gdev;
>  	struct gpio_chip *gc;
>  	int value;
> +	DEFINE_REVOCABLE(rev, desc->gdev->chip_rp);

DEFINE_REVOCABLE() is racy and can lead to use-after-free since nothing
prevents chip_rp from being revoked and freed while the
revocable_alloc() hidden in DEFINE_REVOCABLE() is running.

>  
> -	/* FIXME Unable to use gpio_chip_guard due to const desc. */
> -	gdev = desc->gdev;
> -
> -	guard(srcu)(&gdev->srcu);
> -
> -	gc = srcu_dereference(gdev->chip, &gdev->srcu);
> +	REVOCABLE_TRY_ACCESS_WITH(rev, gc);
>  	if (!gc)
>  		return -ENODEV;

Johan