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From: Linus Walleij <linus.walleij@linaro.org>
Date: Wed, 21 Jul 2021 15:46:44 +0200
Message-ID: <CACRpkdbzAzwrSJmoiO8w5KPV2dL-qxgaeD+gSzL-Gg+cmajsOQ@mail.gmail.com>
Subject: Re: cdev/devm_* issues (was Re: [TECH TOPIC] Rust for Linux)
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Wedson Almeida Filho <wedsonaf@google.com>, Greg KH <greg@kroah.com>, 
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>, 
	James Bottomley <James.Bottomley@hansenpartnership.com>, Mark Brown <broonie@kernel.org>, 
	Roland Dreier <roland@kernel.org>, Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>, 
	"ksummit@lists.linux.dev" <ksummit@lists.linux.dev>, Daniel Vetter <daniel@ffwll.ch>, 
	Bartosz Golaszewski <bgolaszewski@baylibre.com>, 
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>
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On Wed, Jul 14, 2021 at 12:35 AM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:

> To me described scenario sounds rather like an object lifetime possible i=
ssue.
> In any case, shouldn=E2=80=99t VFS guarantee by a reference counting that
> gpiochip_remove() wouldn=E2=80=99t be called while file descriptor is in =
use?
> Or am I looking from the wrong end here?

What happens is that the GPIO device disappears (such as unplugging
a USB GPIO expander) while a multithreaded userspace is hammering
exotic ioctl() commands to the same device like crazy.

Under these circumstances (which should be rare, but you know,
developers) it could happen that an ioctl() sneak in before the
gpio_chip pointer is NULL if I read the code right.

Yours,
Linus Walleij