Hello,
On Tue, 30 Sep 2025 14:16:23 +0800
kernel test robot <[email protected]> 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
