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Message-ID: <1542ef65-508b-45be-ad5c-63ad124cb1a2@samsung.com>
Date: Fri, 16 Feb 2024 13:35:00 +0100
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Subject: Re: [PATCH] gpio: cdev: fix a NULL-pointer dereference with DEBUG
 enabled
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To: Bartosz Golaszewski <brgl@bgdev.pl>, Kent Gibson <warthog618@gmail.com>,
	Linus Walleij <linus.walleij@linaro.org>, "Paul E . McKenney"
	<paulmck@kernel.org>
Cc: linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org, Bartosz
	Golaszewski <bartosz.golaszewski@linaro.org>
From: Marek Szyprowski <m.szyprowski@samsung.com>
In-Reply-To: <20240216105930.16265-1-brgl@bgdev.pl>
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References: <CGME20240216105945eucas1p15af2e143fe2090cd33fabb91ff012571@eucas1p1.samsung.com>
	<20240216105930.16265-1-brgl@bgdev.pl>

On 16.02.2024 11:59, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> We are actually passing the gc pointer to chip_dbg() so we have to
> srcu_dereference() it.
>
> Fixes: 8574b5b47610 ("gpio: cdev: use correct pointer accessors with SRCU")
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Closes: https://lore.kernel.org/lkml/179caa10-5f86-4707-8bb0-fe1b316326d6@samsung.com/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>   drivers/gpio/gpiolib-cdev.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index 85037fa4925e..f384fa278764 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -2795,8 +2795,8 @@ int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt)
>   		return ret;
>   
>   	guard(srcu)(&gdev->srcu);
> -
> -	if (!rcu_access_pointer(gdev->chip))
> +	gc = srcu_dereference(gdev->chip, &gdev->srcu);
> +	if (!gc)
>   		return -ENODEV;
>   
>   	chip_dbg(gc, "added GPIO chardev (%d:%d)\n", MAJOR(devt), gdev->id);

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland