linux-kernel - Re: [PATCH 2/3] gpiolib: use kref in gpio

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Message-ID: <CACRpkdaAYox65p9=Aheu5iomJRGPBc7CvnxJqPeqXdNdunAXPg@mail.gmail.com>
Date:   Sat, 16 May 2020 11:50:45 +0200
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 2/3] gpiolib: use kref in gpio_desc

On Thu, May 14, 2020 at 3:42 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:

> So this "numbing down" of the chip works - in that I don't see any
> splat in the above use-case but right now if nvmem takes an existing
> GPIO descriptor over nvmem_config, then it will call gpiod_put() on it
> and we'll do the same in the provider driver leading to the following
> warning:

Isn't that the WARN_ON(extra_checks) in gpiod_free()?
What part of the if() clause is causing this? I.e.:
if (desc && desc->gdev && gpiod_free_commit(desc)) ...

I suspect gpiod_free_commit() is causing it by returning nonzero.
We could essentially ignore that if and only if the gpio_chip
has been detached from the gpio_device.

This should fix the problem if I'm right.

Yours,
Linus Walleij