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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAD++jL=8ajGZa1RRdH9xERLp7VukGPgJCN2QP1_M6MNDoLPM_A@mail.gmail.com>
Date: Thu, 29 Jan 2026 14:27:40 +0100
From: Linus Walleij <linusw@...nel.org>
To: Johan Hovold <johan@...nel.org>
Cc: Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, 
	"Rafael J . Wysocki" <rafael@...nel.org>, Tzung-Bi Shih <tzungbi@...nel.org>, Jonathan Corbet <corbet@....net>, 
	Shuah Khan <shuah@...nel.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-doc@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <brgl@...nel.org>
Subject: Re: [PATCH 0/3] Revert "revocable: Revocable resource management"

Doing a quick interlude here,

On Wed, Jan 28, 2026 at 4:48 PM Johan Hovold <johan@...nel.org> wrote:

> What I've been trying to get across is that the chardev hot-unplug issue
> is real and needs to be fixed where it still exists, while the manual
> unbinding of drivers by root is a corner case which does not need to be
> addressed at *any* cost.

I agree with Johans stance here.

I might have a skewed view of history and be a bit self-delusional,
but at the time I began the work with the GPIO character device, what
we were seeing were these GPIO adapters on USB.

Those were/are hot-pluggable, and provide GPIOs that are not
for "system critical" things, i.e. not critical for the computer/system
it is running on.

Instead these are things like the Mikroe Clickboard GPIO expander
and TTY, or these GPIOs that come on FTDI USB adapters. These
can and are certainly being used for things that are critical to the thing
they are used for, such as regulating water reserves for your local
hydro power plant. Of course only a madman would unplug that,
but from Linux' POV they are very hot-pluggable, by their very nature.

[Side quest on what are some insanities industrial system people
do here... but these adapters are *very* popular.]

Since they are hot-pluggable and will never appear in DTS files
or such, a character device or other userspace ABI is the right
abstraction, and it needs to be able to come and go without crashing
or wasting memory. Plug/unplug the Mikroe clickboard GPIO
10.000 times should be fine under any circumstances.

And that is the problem that need to be solved *first*, before
removing things on (local) I2C buses or unbinding random devices
from sysfs making them unpluggable in theory.

Yours,
Linus Walleij