linux-kernel - Re: [PATCH v3] gpiolib: fix reference leaks when removing GPIO chips still in use

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Message-ID: <CACRpkdb93yAdW7+YLd0jNK8ZsBXsqNCqpUxnB6ENn-2td+vzmg@mail.gmail.com>
Date:   Tue, 15 Aug 2023 10:25:28 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kent Gibson <warthog618@...il.com>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3] gpiolib: fix reference leaks when removing GPIO chips
 still in use

On Fri, Aug 11, 2023 at 9:30 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.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 == 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@...aro.org>
> ---
> v1 -> v2:
> - add a comment about why we can't use VALIDATE_DESC_VOID()
>
> v2 -> v3:
> - we must drop the reference to the owner module before we drop the one
>   to the gpio_device as the latter may be removed if this is the last
>   reference and we'll end up calling module_put() on freed memory

v3 looks good to me.
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij