linux-kernel - Re: [PATCH 16/22] gpio: reduce the functionality of validate

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Message-ID: <CACRpkdbCBe+HH5uuh94tx9ezV0xtBO-=DZp22bUBbbYuEtJ3Vw@mail.gmail.com>
Date: Wed, 31 Jan 2024 21:16:18 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Kent Gibson <warthog618@...il.com>, Alex Elder <elder@...aro.org>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, "Paul E . McKenney" <paulmck@...nel.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Wolfram Sang <wsa@...-dreams.de>, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 16/22] gpio: reduce the functionality of validate_desc()

On Tue, Jan 30, 2024 at 1:48 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> Checking desc->gdev->chip for NULL without holding it in place with some
> serializing mechanism is pointless. Remove this check. Also don't check
> desc->gdev for NULL as it can never happen.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

I don't know if I agree that it is pointless. It will work on any single-CPU
system and 99.9% of other cases.

On the other hand: what it is supposed to protect against is userspace
doing calls to a gpio_device through the character device, while the
backing struct gpio_chip is gone (e.g. a GPIO expander on USB,
and someone pulled the cable), i.e. it became NULL, and this is why the
error message says "backing device is gone".

But I want to see where the series is going, maybe you fix this
problem in the end, so I can come back and ACK this.

Yours,
Linus Walleij