[PATCH] drm: Avoid connector reference imbalance on error path

[Daniel Vetter]

On Fri, May 06, 2016 at 12:47:45PM +0100, Chris Wilson wrote:
> Whilst looking at the fallout from using connector references for
> atomic, I noticed that there is an early return buried in
> drm_atomic_set_crtc_for_connector() that if hit could cause us to leak a
> reference on the connector.
> 
> Fixes: d2307dea14 (drm/atomic: use connector references (v3))
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Stone <daniels at collabora.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Dave Airlie <airlied at redhat.com>

Applied to drm-misc, thanks.
-Daniel

> ---
>  drivers/gpu/drm/drm_atomic.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 86e89db02ed7..3ff1ed7b33db 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1160,14 +1160,18 @@ drm_atomic_set_crtc_for_connector(struct drm_connector_state *conn_state,
>  {
>  	struct drm_crtc_state *crtc_state;
>  
> -	if (crtc)
> -		drm_connector_reference(conn_state->connector);
> -	if (conn_state->crtc && conn_state->crtc != crtc) {
> +	if (conn_state->crtc == crtc)
> +		return 0;
> +
> +	if (conn_state->crtc) {
>  		crtc_state = drm_atomic_get_existing_crtc_state(conn_state->state,
>  								conn_state->crtc);
>  
>  		crtc_state->connector_mask &=
>  			~(1 << drm_connector_index(conn_state->connector));
> +
> +		drm_connector_unreference(conn_state->connector);
> +		conn_state->crtc = NULL;
>  	}
>  
>  	if (crtc) {
> @@ -1177,18 +1181,16 @@ drm_atomic_set_crtc_for_connector(struct drm_connector_state *conn_state,
>  
>  		crtc_state->connector_mask |=
>  			1 << drm_connector_index(conn_state->connector);
> -	}
>  
> -	if (conn_state->crtc)
> -		drm_connector_unreference(conn_state->connector);
> -	conn_state->crtc = crtc;
> +		drm_connector_reference(conn_state->connector);
> +		conn_state->crtc = crtc;
>  
> -	if (crtc)
>  		DRM_DEBUG_ATOMIC("Link connector state %p to [CRTC:%d:%s]\n",
>  				 conn_state, crtc->base.id, crtc->name);
> -	else
> +	} else {
>  		DRM_DEBUG_ATOMIC("Link connector state %p to [NOCRTC]\n",
>  				 conn_state);
> +	}
>  
>  	return 0;
>  }
> -- 
> 2.8.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch