linux-kernel - Re: [PATCH v2 01/16] drm/panel: get/put panel reference in drm_panel

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Message-ID: <20250620-conscious-purring-ant-b0a64e@houat>
Date: Fri, 20 Jun 2025 11:10:55 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>
Cc: Anusha Srivatsa <asrivats@...hat.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Jessica Zhang <jessica.zhang@....qualcomm.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Inki Dae <inki.dae@...sung.com>, 
	Jagan Teki <jagan@...rulasolutions.com>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Andrzej Hajda <andrzej.hajda@...el.com>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Chen-Yu Tsai <wens@...e.org>, 
	Samuel Holland <samuel@...lland.org>, Seung-Woo Kim <sw0312.kim@...sung.com>, 
	Kyungmin Park <kyungmin.park@...sung.com>, Krzysztof Kozlowski <krzk@...nel.org>, 
	Alim Akhtar <alim.akhtar@...sung.com>, Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>, 
	Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>, Kieran Bingham <kieran.bingham+renesas@...asonboard.com>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Magnus Damm <magnus.damm@...il.com>, 
	Biju Das <biju.das.jz@...renesas.com>, Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, 
	Alain Volmat <alain.volmat@...s.st.com>, Raphael Gallais-Pou <rgallaispou@...il.com>, 
	Stefan Agner <stefan@...er.ch>, Alison Wang <alison.wang@....com>, 
	Linus Walleij <linus.walleij@...aro.org>, Thierry Reding <thierry.reding@...il.com>, 
	Mikko Perttunen <mperttunen@...dia.com>, Jonathan Hunter <jonathanh@...dia.com>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev, linux-samsung-soc@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2 01/16] drm/panel: get/put panel reference in
 drm_panel_add/remove()

On Fri, Jun 20, 2025 at 10:33:53AM +0200, Luca Ceresoli wrote:
> Hello Anusha,
> 
> On Thu, 19 Jun 2025 14:15:53 -0500
> Anusha Srivatsa <asrivats@...hat.com> wrote:
> 
> > Take the panel reference and put it back as required.
> > drm_panel_add() and drm_panel_remove() add a panel to
> > the global registry and removes a panel respectively.
> > Use get() and put() helpers to keep up with refcounting.
> > 
> > Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> > Signed-off-by: Anusha Srivatsa <asrivats@...hat.com>
> 
> This patch is good.
> 
> I'd just point out that this must be applied only after all drivers
> have been converted to the the _alloc API, otherwise with the following
> sequence:
> 
>   panel = devm_kzalloc();
>   drm_panel_init(panel);
>   drm_panel_add(panel);
>   ...
>   drm_panel_remove(panel); <-----
> 
> at the drm_panel_remove() you'd have a warning:
> 
>   refcount_t: addition on 0; use-after-free.
> 
> So, if all panel drivers are converted:

Not all panels are yet:
$ rg -l drm_panel_init -- drivers/gpu/drm/panel/ | wc -l
20

Maxime

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