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From:   Bartosz Golaszewski <brgl@bgdev.pl>
Date:   Thu, 10 Aug 2023 20:57:49 +0200
Message-ID: <CAMRc=Mf8g0JV0QQgpiTS2i+y68NVW-97vOMt+0389++wB1swqw@mail.gmail.com>
Subject: Re: [PATCH v2] gpiolib: fix reference leaks when removing GPIO chips
 still in use
To:     Linus Walleij <linus.walleij@linaro.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Kent Gibson <warthog618@gmail.com>
Cc:     linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
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On Thu, Aug 10, 2023 at 8:48=E2=80=AFPM Bartosz Golaszewski <brgl@bgdev.pl>=
 wrote:
>
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> After we remove a GPIO chip that still has some requested descriptors,
> gpiod_free_commit() will fail and we will never put the references to the
> GPIO device and the owning module in gpiod_free().
>
> Rework this function to:
> - not warn on desc =3D=3D NULL as this is a use-case on which most free
>   functions silently return
> - put the references to desc->gdev and desc->gdev->owner unconditionally
>   so that the release callback actually gets called when the remaining
>   references are dropped by external GPIO users
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

I forgot to pick up Linus' tag. I'll do it when applying. I should
really start using b4...

Bart

> ---
> v1 -> v2:
> - add a comment about why we can't use VALIDATE_DESC_VOID()
>
>  drivers/gpio/gpiolib.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 251c875b5c34..2158067c4fd2 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2167,12 +2167,18 @@ static bool gpiod_free_commit(struct gpio_desc *d=
esc)
>
>  void gpiod_free(struct gpio_desc *desc)
>  {
> -       if (desc && desc->gdev && gpiod_free_commit(desc)) {
> -               module_put(desc->gdev->owner);
> -               gpio_device_put(desc->gdev);
> -       } else {
> +       /*
> +        * We must not use VALIDATE_DESC_VOID() as the underlying gdev->c=
hip
> +        * may already be NULL but we still want to put the references.
> +        */
> +       if (!desc)
> +               return;
> +
> +       if (!gpiod_free_commit(desc))
>                 WARN_ON(extra_checks);
> -       }
> +
> +       gpio_device_put(desc->gdev);
> +       module_put(desc->gdev->owner);
>  }
>
>  /**
> --
> 2.39.2
>