linux-kernel - Re: [PATCH 22/23] gpiolib: Leverage revocable for other independent lifecycle instances

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Message-ID: <aXjgN2jGsaNQgP9o@google.com>
Date: Tue, 27 Jan 2026 15:56:39 +0000
From: Tzung-Bi Shih <tzungbi@...nel.org>
To: Johan Hovold <johan@...nel.org>
Cc: Benson Leung <bleung@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Bartosz Golaszewski <brgl@...ev.pl>,
	Linus Walleij <linusw@...nel.org>, Jonathan Corbet <corbet@....net>,
	Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, chrome-platform@...ts.linux.dev,
	linux-kselftest@...r.kernel.org,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	Simona Vetter <simona.vetter@...ll.ch>,
	Dan Williams <dan.j.williams@...el.com>,
	Jason Gunthorpe <jgg@...dia.com>, linux-gpio@...r.kernel.org
Subject: Re: [PATCH 22/23] gpiolib: Leverage revocable for other independent
 lifecycle instances

On Mon, Jan 26, 2026 at 02:58:17PM +0100, Johan Hovold wrote:
> On Sat, Jan 24, 2026 at 05:52:53PM +0100, Johan Hovold wrote:
> > On Fri, Jan 16, 2026 at 08:10:35AM +0000, Tzung-Bi Shih wrote:
> > > There are independent lifecycle instances (e.g., other drivers) can save
> > > a raw pointer to the struct gpio_device (e.g., via gpio_device_find())
> > > or struct gpio_desc (e.g., via gpio_to_desc()).  In some operations,
> > > they have to access the underlying struct gpio_chip.
> > > 
> > > Leverage revocable for them so that they don't need to handle the
> > > synchronization by accessing the SRCU explicitly.
> > > 
> > > Signed-off-by: Tzung-Bi Shih <tzungbi@...nel.org>
> > 
> > >  static int gpiod_get_raw_value_commit(const struct gpio_desc *desc)
> > >  {
> > > -	struct gpio_device *gdev;
> > >  	struct gpio_chip *gc;
> > >  	int value;
> > > +	DEFINE_REVOCABLE(rev, desc->gdev->chip_rp);
> > 
> > DEFINE_REVOCABLE() is racy and can lead to use-after-free since nothing
> > prevents chip_rp from being revoked and freed while the
> > revocable_alloc() hidden in DEFINE_REVOCABLE() is running.
> 
> This was supposed to say "revocable_init()" (i.e. revocable_alloc()
> without the memory allocation).

I see the issue.  Thanks for identifying this.