Re: [PATCH v3.1 3/3] drm/i915: Don't try to remove MST cleanly when force removed.

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Aug 06, 2015 at 01:47:37PM +0200, Maarten Lankhorst wrote:
> Physically disconnecting a DP connector with an active MST stream
> can lead to a kernel panic in intel_mst_disable_dp when calling
> drm_dp_update_payload_part1. Examining the code it seems that the
> port is freed while work to remove the connector is scheduled.
> 
> This probably means it's fine to skip call all the mst helper calls
> and only attempt to disable the real encoder.

I think this is a refcounting bug in the dp mst helpers, the port
shouldn't just go poof when we still hold a reference to it. Can you
please try to figure out what's really broken here, and if that's too
tricky add a big FIXME comment?

Thanks, Daniel

> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp_mst.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
> index 91ad17110c2f..19c9e49d74e0 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -110,6 +110,9 @@ static void intel_mst_disable_dp(struct intel_encoder *encoder)
>  
>  	DRM_DEBUG_KMS("%d\n", intel_dp->active_mst_links);
>  
> +	if (!intel_mst->port)
> +		return;
> +
>  	drm_dp_mst_reset_vcpi_slots(&intel_dp->mst_mgr, intel_mst->port);
>  
>  	ret = drm_dp_update_payload_part1(&intel_dp->mst_mgr);
> @@ -126,12 +129,14 @@ static void intel_mst_post_disable_dp(struct intel_encoder *encoder)
>  
>  	DRM_DEBUG_KMS("%d\n", intel_dp->active_mst_links);
>  
> -	/* this can fail */
> -	drm_dp_check_act_status(&intel_dp->mst_mgr);
> -	/* and this can also fail */
> -	drm_dp_update_payload_part2(&intel_dp->mst_mgr);
> +	if (intel_mst->port) {
> +		/* this can fail */
> +		drm_dp_check_act_status(&intel_dp->mst_mgr);
> +		/* and this can also fail */
> +		drm_dp_update_payload_part2(&intel_dp->mst_mgr);
>  
> -	drm_dp_mst_deallocate_vcpi(&intel_dp->mst_mgr, intel_mst->port);
> +		drm_dp_mst_deallocate_vcpi(&intel_dp->mst_mgr, intel_mst->port);
> +	}
>  
>  	intel_dp->active_mst_links--;
>  	intel_mst->port = NULL;
> @@ -471,9 +476,13 @@ static void intel_dp_destroy_mst_connector(struct drm_dp_mst_topology_mgr *mgr,
>  	/* need to nuke the connector */
>  	drm_modeset_lock_all(dev);
>  	if (connector->state->crtc) {
> +		struct drm_encoder *encoder = connector->state->best_encoder;
> +		struct intel_dp_mst_encoder *intel_mst = enc_to_mst(encoder);
>  		struct drm_mode_set set;
>  		int ret;
>  
> +		intel_mst->port = NULL;
> +
>  		memset(&set, 0, sizeof(set));
>  		set.crtc = connector->state->crtc,
>  
> -- 
> 2.1.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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