linux-kernel - Re: [PATCH 2/2] drm/bridge: ti-sn65dsi83: protect device resources on unplug

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] [day] [month] [year] [list]

Message-ID: <20250827-charming-arcane-stingray-cfb8b6@houat>
Date: Wed, 27 Aug 2025 09:46:03 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Hui Pu <Hui.Pu@...ealthcare.com>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	Dmitry Baryshkov <lumag@...nel.org>
Subject: Re: [PATCH 2/2] drm/bridge: ti-sn65dsi83: protect device resources
 on unplug

On Wed, Aug 20, 2025 at 01:13:02PM +0200, Luca Ceresoli wrote:
> Hello Maxime,
> 
> On Tue, 19 Aug 2025 14:29:32 +0200
> Maxime Ripard <mripard@...nel.org> wrote:
> 
> > > @@ -1005,7 +1041,24 @@ static void sn65dsi83_remove(struct i2c_client *client)
> > >  {
> > >  	struct sn65dsi83 *ctx = i2c_get_clientdata(client);
> > >  
> > > +	drm_bridge_unplug(&ctx->bridge);
> > >  	drm_bridge_remove(&ctx->bridge);  
> > 
> > Shouldn't we merge drm_bridge_unplug with the release part of
> > devm_drm_bridge_alloc?
> 
> I'm not sure I got what you are suggesting here, sorry.
> 
> Do you mean that __devm_drm_bridge_alloc() should add a devres action
> to call drm_bridge_unplug(), so the unplug is called implicitly and
> does not need to be called explicitly by all drivers?

Yes

> If that's what you mean, I don't think that would work. Unless I'm
> missing something, devres actions are always invoked just after the
> driver .remove callback.

Yes, they are called in reverse order of registration, after remove.

> But we need to call drm_bridge_unplug() at the beginning (or just
> before) .remove, at least for drivers that need to do something in
> .remove that cannot be done by devm.
> 
> In pseudocode:
> 
> mybridge_remove()
> {
>   drm_bridge_unplug(); <-- explicit call as in my patch
>   xyz_disable();
>   drm_bridge_unplug(); <-- implicitly done by devres
> }
> 
> We want xyz_disable() to be done after drm_bridge_unplug(), so other
> code paths using drm_bridge_enter/exit() won't mess with xyz.

It's not clear to me why doing it before xyz_disable() is important
here? If anything, it would prevent from disabling the hardware for
example, even though you still have your memory mapping, clocks, power
domains, regulators, etc. to properly disable it.

You're still correct that it's a bad idea though because we want to do
it before we start freeing all those, so it needs to execute as the
before the devm actions ...

> devres actions cannot be added to be executed _before_ .remove, AFAIK.

... and we can't do that either.

Maxime

Download attachment "signature.asc" of type "application/pgp-signature" (274 bytes)