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

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Message-ID: <CAMRc=McrFa42mNWmZtD1HKKKZ+USUKpQAAME50wbfxPM7L72gA@mail.gmail.com>
Date: Mon, 19 Jan 2026 09:33:21 +0100
From: Bartosz Golaszewski <brgl@...nel.org>
To: Tzung-Bi Shih <tzungbi@...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 Sat, Jan 17, 2026 at 1:48 PM Tzung-Bi Shih <tzungbi@...nel.org> wrote:
>
> 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`.

Yeah, no, there's no dedicated performance measurement in GLib tests,
I just timed the test-suite and it runs 40% slower with this series.

Bartosz