linux-kernel - Re: [PATCH 0/3] Revert "revocable: Revocable resource management"

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Message-ID: <20260124184239.GO215800@killaraus>
Date: Sat, 24 Jan 2026 20:42:39 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Johan Hovold <johan@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Tzung-Bi Shih <tzungbi@...nel.org>,
	Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>,
	Linus Walleij <linusw@...nel.org>, Jonathan Corbet <corbet@....net>,
	Shuah Khan <shuah@...nel.org>,
	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-doc@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] Revert "revocable: Revocable resource management"

On Sat, Jan 24, 2026 at 06:05:32PM +0100, Johan Hovold wrote:
> I was surprised to learn that the revocable functionality was merged last week
> given the community feedback on list and at LPC, but not least since there are
> no users of it, which we are supposed to require to be able to evaluate it
> properly.
> 
> The chromeos ec driver issue which motivated this work turned out not to need
> it as was found during review. And the example gpiolib conversion was posted
> the very same morning that this was merged which hardly provides enough time
> for evaluation (even if Bartosz quickly reported a performance regression).
> 
> Turns out there are correctness issues with both the gpiolib conversion and
> the revocable design itself that can lead to use-after-free and hung tasks (see
> [1] and patch 3/3).
> 
> And as was pointed out repeatedly during review, and again at the day of the
> merge, this does not look like the right interface for the chardev unplug
> issue.
> 
> Revert the revocable implementation until a redesign has been proposed and
> evaluated properly.

I have voiced some of the concerns listed above. This was merge way too
quickly, without proper review and evaluation of the API as a solution
for the problem at hand. I don't want to see this API spreading through
drivers the same way devm_kzalloc() did without developers understanding
the limitations, it's just another recipe for disaster. I trust that we
have enough knowledge and wisdom in the community to implement correct
solutions to the producer-consumer races.

Acked-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> [1] https://lore.kernel.org/all/aXT45B6vLf9R3Pbf@hovoldconsulting.com/
> 
> 
> Johan Hovold (3):
>   Revert "selftests: revocable: Add kselftest cases"
>   Revert "revocable: Add Kunit test cases"
>   Revert "revocable: Revocable resource management"
> 
>  .../driver-api/driver-model/index.rst         |   1 -
>  .../driver-api/driver-model/revocable.rst     | 152 -----------
>  MAINTAINERS                                   |   9 -
>  drivers/base/Kconfig                          |   8 -
>  drivers/base/Makefile                         |   5 +-
>  drivers/base/revocable.c                      | 241 ------------------
>  drivers/base/revocable_test.c                 | 142 -----------
>  include/linux/revocable.h                     |  69 -----
>  tools/testing/selftests/Makefile              |   1 -
>  .../selftests/drivers/base/revocable/Makefile |   7 -
>  .../drivers/base/revocable/revocable_test.c   | 136 ----------
>  .../drivers/base/revocable/test-revocable.sh  |  39 ---
>  .../base/revocable/test_modules/Makefile      |  10 -
>  .../revocable/test_modules/revocable_test.c   | 195 --------------
>  14 files changed, 1 insertion(+), 1014 deletions(-)
>  delete mode 100644 Documentation/driver-api/driver-model/revocable.rst
>  delete mode 100644 drivers/base/revocable.c
>  delete mode 100644 drivers/base/revocable_test.c
>  delete mode 100644 include/linux/revocable.h
>  delete mode 100644 tools/testing/selftests/drivers/base/revocable/Makefile
>  delete mode 100644 tools/testing/selftests/drivers/base/revocable/revocable_test.c
>  delete mode 100755 tools/testing/selftests/drivers/base/revocable/test-revocable.sh
>  delete mode 100644 tools/testing/selftests/drivers/base/revocable/test_modules/Makefile
>  delete mode 100644 tools/testing/selftests/drivers/base/revocable/test_modules/revocable_test.c

-- 
Regards,

Laurent Pinchart