linux-kernel - Re: [PATCH] gpiolib: revert the attempt to protect the GPIO device list with an rwsem

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Message-ID: <CAMRc=McJEbeL-Esc5=ycNnTfQc8diQ8esgNjKDiG6rKDnT1CJA@mail.gmail.com>
Date: Wed, 17 Jan 2024 09:55:12 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] gpiolib: revert the attempt to protect the GPIO device
 list with an rwsem

On Mon, Jan 15, 2024 at 12:17 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> This reverts commits 1979a2807547 ("gpiolib: replace the GPIO device
> mutex with a read-write semaphore") and 65a828bab158 ("gpiolib: use
> a mutex to protect the list of GPIO devices").
>
> Unfortunately the legacy GPIO API that's still used in older code has to
> translate numbers from the global GPIO numberspace to descriptors. This
> results in a GPIO device lookup in every call to legacy functions. Some
> of those functions - like gpio_set/get_value() - can be called from
> atomic context so taking a sleeping lock that is an RW semaphore results
> in an error.
>
> We'll probably have to protect this list with SRCU.
>
> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> Closes: https://lore.kernel.org/linux-wireless/f7b5ff1e-8f34-4d98-a7be-b826cb897dc8@moroto.mountain/
> Fixes: 1979a2807547 ("gpiolib: replace the GPIO device mutex with a read-write semaphore")
> Fixes: 65a828bab158 ("gpiolib: use a mutex to protect the list of GPIO devices")
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> ---

Patch queued for fixes for this merge window.

Bart