linux-kernel - Re: [PATCH v7 1/3] revocable: Revocable resource management

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Message-ID: <CAMRc=McsrthHS4kcV7UkmdVFS4nr9vXe8Z_kQODvMUYxVkE8KQ@mail.gmail.com>
Date: Fri, 16 Jan 2026 19:31:51 +0100
From: Bartosz Golaszewski <brgl@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Danilo Krummrich <dakr@...nel.org>, Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	Tzung-Bi Shih <tzungbi@...nel.org>, Benson Leung <bleung@...omium.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J . Wysocki" <rafael@...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, 
	Wolfram Sang <wsa+renesas@...g-engineering.com>, Simona Vetter <simona.vetter@...ll.ch>, 
	Dan Williams <dan.j.williams@...el.com>, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v7 1/3] revocable: Revocable resource management

On Fri, Jan 16, 2026 at 7:24 PM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> On Fri, Jan 16, 2026 at 07:19:50PM +0100, Bartosz Golaszewski wrote:
> > On Fri, Jan 16, 2026 at 5:41 PM Danilo Krummrich <dakr@...nel.org> wrote:
> > >
> > > On Fri Jan 16, 2026 at 5:04 PM CET, Laurent Pinchart wrote:
> > > > Based on the discussions we had at LPC, the revocable resource management API
> > > > is not the right solution to handle races between device removal and userspace
> > > > access.
> > >
> > > Please see: https://lore.kernel.org/all/DFQ5D44A0348.PZJIGPL972N@kernel.org/
> > >
> > > > It is however a possibly useful tool for races between producers and consumers
> > > > *inside the kernel*.
> > >
> > > Do you have an example for such a case?
> >
> > Isn't the GPIO use-case - which the series on top of it addresses - one?
> >
> > With fw_devlink=off it's quite easy to trigger all kinds of crashes
> > with in-kernel users.
>
> Does this series solve that? It looked to me like it just replaces the
> existing SRCU with a wrapper?
>

SRCU already *did* solve it. Revocable *is* a wrapper around SRCU that
generalizes the initial solution.

Replacing SRCU with a generalized wrapper is fine but there are
subsystems out there, where the problem is much less trivial. Take I2C
for example: the struct device management is so broken that there
isn't even anything *to revoke* yet. It'll take years of little
reworks before we can even use revocable at all.

I'm not against it as a library of functions. But TBH I looked at the
series and - besides making the code run slower - it also kind of
makes it harder to read. With *naked* SRCU it's very clear what's
going on, when you start hiding the logic, it becomes needlessly
obfuscated.

I want to first see revocable match current GPIO performance and then
we can talk about accepting it.

Bartosz