linux-kernel - [PATCH RESEND v4 3/7] drm/bridge: drm_bridge_attach: lock the encoder chain mutex during insertion

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Message-Id: <20260113-drm-bridge-alloc-encoder-chain-mutex-v4-3-60f3135adc45@bootlin.com>
Date: Tue, 13 Jan 2026 19:47:14 +0100
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>, 
 Ian Ray <ian.ray@...ealthcare.com>
Subject: [PATCH RESEND v4 3/7] drm/bridge: drm_bridge_attach: lock the
 encoder chain mutex during insertion

drm_bridge_attach() modifies the encoder bridge chain, so take a mutex
around such operations to allow users of the chain to protect themselves
from chain modifications while iterating.

Reviewed-by: Maxime Ripard <mripard@...nel.org>
Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---

Changes in v3:
- Lock encoder->bridge_chain_mutex directly, no wrappers

Changes in v2:
- Removed comment before on drm_bridge_detach()
---
 drivers/gpu/drm/drm_bridge.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 8f355df883d8..c8389383e0d2 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -462,10 +462,12 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
 	bridge->dev = encoder->dev;
 	bridge->encoder = encoder;
 
+	mutex_lock(&encoder->bridge_chain_mutex);
 	if (previous)
 		list_add(&bridge->chain_node, &previous->chain_node);
 	else
 		list_add(&bridge->chain_node, &encoder->bridge_chain);
+	mutex_unlock(&encoder->bridge_chain_mutex);
 
 	if (bridge->funcs->attach) {
 		ret = bridge->funcs->attach(bridge, encoder, flags);
@@ -496,7 +498,9 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
 err_reset_bridge:
 	bridge->dev = NULL;
 	bridge->encoder = NULL;
+	mutex_lock(&encoder->bridge_chain_mutex);
 	list_del(&bridge->chain_node);
+	mutex_unlock(&encoder->bridge_chain_mutex);
 
 	if (ret != -EPROBE_DEFER)
 		DRM_ERROR("failed to attach bridge %pOF to encoder %s: %d\n",

-- 
2.52.0