drm/dp/mst: close deadlock in connector destruction.

I've only seen this once, and I failed to capture the
lockdep backtrace, but I did some investigations.

If we are calling into the MST layer from EDID probing,
we have the mode_config mutex held, if during that EDID
probing, the MST hub goes away, then we can get a deadlock
where the connector destruction function in the driver
tries to retake the mode config mutex.

This offloads connector destruction to a workqueue,
and avoid the subsequenct lock ordering issue.

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

2 files changed, 6 insertions, 0 deletions

diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 3b4d8a4..57ca8cc 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -743,6 +743,8 @@ struct drm_connector {
 	uint8_t num_h_tile, num_v_tile;
 	uint8_t tile_h_loc, tile_v_loc;
 	uint16_t tile_h_size, tile_v_size;
+
+	struct list_head destroy_list;
 };
 
 /**
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index a250781..86d0b25 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -463,6 +463,10 @@ struct drm_dp_mst_topology_mgr {
 	struct work_struct work;
 
 	struct work_struct tx_work;
+
+	struct list_head destroy_connector_list;
+	struct mutex destroy_connector_lock;
+	struct work_struct destroy_connector_work;
 };
 
 int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr, struct device *dev, struct drm_dp_aux *aux, int max_dpcd_transaction_bytes, int max_payloads, int conn_base_id);