linux-kernel - Re: [PATCH 20/22] gpio: protect the pointer to gpio_chip in gpio

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Message-ID: <CACRpkdaBPWOd-MwQvkWCJaua6sbPTBxeK7TV+79SvvGkzCW_4Q@mail.gmail.com>
Date: Wed, 31 Jan 2024 21:23:17 +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 20/22] gpio: protect the pointer to gpio_chip in
 gpio_device with SRCU

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

> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> Ensure we cannot crash if the GPIO device gets unregistered (and the
> chip pointer set to NULL) during any of the API calls.
>
> To that end: wait for all users of gdev->chip to exit their read-only
> SRCU critical sections in gpiochip_remove().
>
> For brevity: add a guard class which can be instantiated at the top of
> every function requiring read-only access to the chip pointer and use it
> in all API calls taking a GPIO descriptor as argument. In places where
> we only deal with the GPIO device - use regular guard() helpers and
> rcu_dereference() for chip access. Do the same in API calls taking a
> const pointer to gpio_desc.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

The way I read it after this the gpio character device is well protected
against the struct gpio_chip going away, good work!
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

I would perhaps slot in some documentation around
struct gpio_chip_guard explaining how this works and why it is needed.

Yours,
Linus Walleij