Re: [PATCH v5 3/7] drm/bridge: drm_bridge_attach: lock the encoder chain mutex during insertion

[Louis Chauvet <louis.chauvet@bootlin.com>]

On 3/24/26 9:58 AM, Luca Ceresoli wrote:
> 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>

Reviewed-by: Louis Chauvet <louis.chauvet@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 30d957675d87..42ca4b243579 100644
> --- 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",
>