linux-kernel - Re: [PATCH RESEND] gpiolib: hold gpio devices lock until ->descs array is initialised

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Message-ID: <CACRpkdYGED-YU8PGUFwK-Arrs0Vp1=Oc-Nx=MvjuygLJvzQPkg@mail.gmail.com>
Date:   Thu, 23 Jan 2020 16:26:11 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Dan Callaghan <dan.callaghan@...ngear.com>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] gpiolib: hold gpio devices lock until ->descs
 array is initialised

On Tue, Jan 21, 2020 at 1:13 AM Dan Callaghan
<dan.callaghan@...ngear.com> wrote:

> If a driver consuming the GPIO chip is being probed at the same time as
> the GPIO driver is registering the chip, it is possible for the
> consuming driver to see the ->descs array in an uninitialised state.
> For example, the gpio-keys-polled driver can fail like this:
>
>     kernel: gpiod_request: invalid GPIO (no device)
>     kernel: gpio-keys-polled PRP0001:07: failed to get gpio: -22
>     kernel: gpio-keys-polled: probe of PRP0001:07 failed with error -22
>
> This patch makes gpiochip_add() hold the lock protecting gpio_devices
> until it has finished setting desc->gdev on the newly inserted list
> entry.
>
> Signed-off-by: Dan Callaghan <dan.callaghan@...ngear.com>
> ---
> Resending this one because I failed to cc the maintainers on the
> original posting, sorry about that.

This makes a lot of sense, I'm impressed that you managed to
provoke this error!

Patch applied.

Yours,
Linus Walleij