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>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.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 8f355df883d8ac8de9d361ec302f4ccbf3bca0d6..c8389383e0d286c0d576ae1864ee783e002d44be 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",

-- 
2.51.1