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Message-ID: <20251002173331.3d06d7d3@booty>
Date: Thu, 2 Oct 2025 17:33:31 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: kernel test robot <oliver.sang@...el.com>
Cc: <oe-lkp@...ts.linux.dev>, <lkp@...el.com>,
<dri-devel@...ts.freedesktop.org>, 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>, 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>, Hui Pu
<Hui.Pu@...ealthcare.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] drm/bridge: lock the encoder chain in scoped
for_each loops
Hello,
On Tue, 30 Sep 2025 14:16:23 +0800
kernel test robot <oliver.sang@...el.com> wrote:
> [ 674.477504][ C1] watchdog: BUG: soft lockup - CPU#1 stuck for 626s! [swapper/0:1]
> [ 674.477539][ C1] CPU#1 Utilization every 96s during lockup:
> [ 674.477543][ C1] #1: 100% system, 1% softirq, 1% hardirq, 0% idle
> [ 674.477549][ C1] #2: 100% system, 1% softirq, 1% hardirq, 0% idle
> [ 674.477553][ C1] #3: 100% system, 0% softirq, 1% hardirq, 0% idle
> [ 674.477557][ C1] #4: 100% system, 1% softirq, 1% hardirq, 0% idle
> [ 674.477561][ C1] #5: 100% system, 1% softirq, 1% hardirq, 0% idle
...
> [ 674.477713][ C1] drm_atomic_add_encoder_bridges (drivers/gpu/drm/drm_atomic.c:1319 (discriminator 1025))
The one reported is an actual bug, causing an infinite loop when the
encoder bridge chain is empty. Took a while to reproduce and debug, but
the fix is very simple:
#define drm_for_each_bridge_in_chain_scoped(encoder, bridge) \
for (struct drm_bridge *bridge __free(drm_bridge_encoder_chain_unlock) = \
- list_first_entry(&drm_encoder_chain_lock(encoder)->bridge_chain, \
+ list_first_entry_or_null(&drm_encoder_chain_lock(encoder)->bridge_chain, \
Fix queued for v2.
Luca
--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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