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@kernel.org>
Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Link: https://patch.msgid.link/20260324-drm-bridge-alloc-encoder-chain-mutex-v5-3-8bf786c5c7e6@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index ba80bebb5685693517cadf7633679228b87c6b1c..fed8f1f06d949d66558da2131255ae27c89d5cde 100644 (file)
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -574,10 +574,12 @@ 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);
@@ -594,7 +596,9 @@ 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",