Re: [PATCH 16/22] gpio: reduce the functionality of validate_desc()

[Linus Walleij]

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

> From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>

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