linux-kernel - [PATCH 2/7] drm/encoder: drm_encoder_cleanup: take chain mutex while tearing down

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Message-Id: <20250926-drm-bridge-alloc-encoder-chain-mutex-v1-2-23b62c47356a@bootlin.com>
Date: Fri, 26 Sep 2025 17:59:43 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: 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>
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: [PATCH 2/7] drm/encoder: drm_encoder_cleanup: take chain mutex
 while tearing down

drm_encoder_cleanup() modifies the encoder chain by removing bridges via
drm_bridge_detach(). Protect this whole operation by taking the mutex, so
any users iterating over the chain will not access it during the change.

Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
 drivers/gpu/drm/drm_encoder.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/drm_encoder.c b/drivers/gpu/drm/drm_encoder.c
index 3261f142baea30c516499d23dbf8d0acf5952cd6..3a04bedf9b759acd6826864b7f2cc9b861a8f170 100644
--- a/drivers/gpu/drm/drm_encoder.c
+++ b/drivers/gpu/drm/drm_encoder.c
@@ -195,9 +195,11 @@ void drm_encoder_cleanup(struct drm_encoder *encoder)
 	 * the indices on the drm_encoder after us in the encoder_list.
 	 */
 
+	mutex_lock(&encoder->bridge_chain_mutex);
 	list_for_each_entry_safe(bridge, next, &encoder->bridge_chain,
 				 chain_node)
 		drm_bridge_detach(bridge);
+	mutex_unlock(&encoder->bridge_chain_mutex);
 
 	drm_mode_object_unregister(dev, &encoder->base);
 	kfree(encoder->name);

-- 
2.51.0