linux-kernel - Re: [PATCH v3 2/7] gpiolib: use kref in gpio

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Fri, 21 Feb 2020 14:40:52 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Khouloud Touil <ktouil@...libre.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v3 2/7] gpiolib: use kref in gpio_desc

On Wed, Feb 19, 2020 at 10:22 AM Bartosz Golaszewski <brgl@...ev.pl> wrote:

> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>
> GPIO descriptors are freed by consumers using gpiod_put(). The name of
> this function suggests some reference counting is going on but it's not
> true.
>
> Use kref to actually introduce reference counting for gpio_desc objects.
> Add a corresponding gpiod_get() helper for increasing the reference count.
>
> This doesn't change anything for already existing (correct) drivers but
> allows us to keep track of GPIO descs used by multiple users.
>
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>

I really like the simplicity of this approach ... hm!
It seems the only downside is a krefcount_t extra per gpio_desc
which is an atomic_t so I guess 32 or 64 bits per desc depending
on arch.

We discussed refcounts in gpiods in another context but it got
really complicated there. This is a clearly cut usecase.

Yours,
Linus Walleij