linux-kernel - Re: [PATCH v2 0/3] drm/display: bridge_connector: get/put the stored bridges: fix NULL pointer regression

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Message-ID: <5954683.DvuYhMxLoT@workhorse>
Date: Mon, 27 Oct 2025 15:44:33 +0100
From: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
To: Marek Szyprowski <m.szyprowski@...sung.com>,
 Naresh Kamboju <naresh.kamboju@...aro.org>,
 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>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Luca Ceresoli <luca.ceresoli@...tlin.com>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject:
 Re: [PATCH v2 0/3] drm/display: bridge_connector: get/put the stored bridges:
 fix NULL pointer regression

On Friday, 17 October 2025 18:15:03 Central European Standard Time Luca Ceresoli wrote:
> A patch of mine recently merged in drm-misc-next [1] has a NULL pointer
> deref regression (reported here [2] and here [3]). Being in lack of a quick
> fix, I sent a revert proposal [4].
> 
> The revert proposal has no answers currenty, and in the meanwhile I have a
> patch that implements the original idea but without the same bug. So here's
> a v2 series with:
> 
>  - the same revert patch
>  - the original patch but rewritten without the same bug (and even simpler)
> 
> Also the re-written patch is now split in two for clarity because it was
> doing two somewhat different things.
> 
> [1] https://lore.kernel.org/all/20250926-drm-bridge-alloc-getput-bridge-connector-v2-1-138b4bb70576@bootlin.com/
> [2] https://lore.kernel.org/lkml/336fbfdd-c424-490e-b5d1-8ee84043dc80@samsung.com/
> [3] https://lore.kernel.org/lkml/CA+G9fYuKHp3QgPKjgFY3TfkDdh5Vf=Ae5pCW+eU41Bu=D7th2g@mail.gmail.com/
> [4] https://lore.kernel.org/lkml/20251016-drm-bridge-alloc-getput-bridge-connector-fix-hdmi_cec-v1-1-81d6984c5361@bootlin.com/
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> ---
> Changes in v2:
> - No changes to the revert patch
> - Added the (corrected) patch introducing the same feature as the original
>   buggy patch, and also split it in two fir clarity
> - Link to v1: https://lore.kernel.org/r/20251016-drm-bridge-alloc-getput-bridge-connector-fix-hdmi_cec-v1-1-81d6984c5361@bootlin.com
> 
> ---
> Luca Ceresoli (3):
>       Revert "drm/display: bridge_connector: get/put the stored bridges"
>       drm/display: bridge_connector: get/put the stored bridges
>       drm/display: bridge_connector: get/put the panel_bridge
> 
>  drivers/gpu/drm/display/drm_bridge_connector.c | 92 +++++++++++---------------
>  1 file changed, 39 insertions(+), 53 deletions(-)
> ---
> base-commit: 84a0a3f014cda68ff10b8517d09e9f0c1cd942a2
> change-id: 20251016-drm-bridge-alloc-getput-bridge-connector-fix-hdmi_cec-9a429ddb48e2
> 
> Best regards,
> 

Tested-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>

Fixes a null pointer dereference on boot on my Radxa ROCK 5T
(RK3588) that's present in next-20251027.

Kind regards,
Nicolas Frattaroli