linux-kernel - Re: [PATCH 00/23] gpiolib: Adopt revocable mechanism for UAF prevention

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Message-ID: <aWuFBqIfJpDL9g-J@tzungbi-laptop>
Date: Sat, 17 Jan 2026 20:48:06 +0800
From: Tzung-Bi Shih <tzungbi@...nel.org>
To: Bartosz Golaszewski <brgl@...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>,
	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 00/23] gpiolib: Adopt revocable mechanism for UAF
 prevention

On Fri, Jan 16, 2026 at 11:35:00AM +0100, Bartosz Golaszewski wrote:
> On Fri, Jan 16, 2026 at 9:11 AM Tzung-Bi Shih <tzungbi@...nel.org> wrote:
> >
> > This series transitions the UAF prevention logic within the GPIO core
> > (gpiolib) to use the 'revocable' mechanism.
> >
> > The existing code aims to prevent UAF issues when the underlying GPIO
> > chip is removed.  This series replaces that custom logic with the
> > generic 'revocable' API, which is designed to handle such lifecycle
> > dependencies.  There should be no change in behavior.
> >
> > This series depends on the 'revocable' API, introduced in [1].  Some
> > build bots may report errors due to undefined symbols related to
> > 'revocable' until the dependency is merged.
> >
> 
> Hi Tzung-Bi!
> 
> Thank you for doing this and considering my suggestions from LPC. I
> haven't looked at the code yet but I quickly tested the series with my
> regular test-suites. The good news is: nothing is broken, every test
> works fine. The bad news is: there seems to be a significant impact on
> performance. With the user-space test-suite from libgpiod (for core C
> library - gpiod-test) I'm seeing a consistent 40% impact on
> performance. That's not really acceptable. :( I will try to bisect the
> series later and see which part exactly breaks it.
> 
> I can also help you with user-space testing with libgpiod, if you need
> it? Some documentation is available here:
> https://libgpiod.readthedocs.io/en/latest/testing.html

How to get the performance data?

I tried on libgpiod-2.2.2.tar.xz:
- ./configure --enable-tools --enable-tests
- make
- ./tests/gpiod-test

There is only TAP output.  Also I don't see the difference between:
`./tests/gpiod-test` vs. `./tests/gpiod-test -m perf`.