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.
This change does not apply to drm_bridge_detach() because: * only the drm_encoder.c calls it, not bridge drivers (unlike drm_bridge_attach()) * the only drm_bridge_detach() caller is drm_encoder_cleanup() which already locks the mutex for the entire cleanup loop, thus additionally locking it here would deadlock * drm_bridge_detach() is recursively calling itself along the chain, so care would be needed to avoid deadlocks Add a comment to clarify that is intended. Signed-off-by: Luca Ceresoli <[email protected]> --- drivers/gpu/drm/drm_bridge.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index 630b5e6594e0affad9ba48791207c7b403da5db8..90e467cf91a134342c80d2f958b928472aaf0d8b 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -453,10 +453,12 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge, bridge->dev = encoder->dev; bridge->encoder = encoder; + drm_encoder_chain_lock(encoder); if (previous) list_add(&bridge->chain_node, &previous->chain_node); else list_add(&bridge->chain_node, &encoder->bridge_chain); + drm_encoder_chain_unlock(encoder); if (bridge->funcs->attach) { ret = bridge->funcs->attach(bridge, encoder, flags); @@ -487,7 +489,9 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge, err_reset_bridge: bridge->dev = NULL; bridge->encoder = NULL; + drm_encoder_chain_lock(encoder); list_del(&bridge->chain_node); + drm_encoder_chain_unlock(encoder); if (ret != -EPROBE_DEFER) DRM_ERROR("failed to attach bridge %pOF to encoder %s: %d\n", @@ -503,6 +507,11 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge, } EXPORT_SYMBOL(drm_bridge_attach); +/* + * Invoked by the encoder during encoder cleanup in drm_encoder_cleanup(), + * so should generally *not* be called by driver code. As opposed to + * drm_bridge_attach(), does not lock the encoder chain mutex. + */ void drm_bridge_detach(struct drm_bridge *bridge) { if (WARN_ON(!bridge)) -- 2.51.0
