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.

Dave Airlie committed 11 years ago

Commit 6b8eeca1 parent 8b72ce13 files · +44 −2Browse files

Unified · Split

3 files

drivers/gpu/drm/drm_dp_mst_topology.c +38 −2
include/drm/drm_crtc.h +2 −0
include/drm/drm_dp_mst_helper.h +4 −0

drivers/gpu/drm/drm_dp_mst_topology.c+38−2

@@ -867,8 +867,16 @@ static void drm_dp_destroy_port(struct kref *kref) · 866 unmodified lines
867	867	port->vcpi.num_slots = 0;
868	868
869	869	kfree(port->cached_edid);
870		− if (port->connector)
871		− (*port->mgr->cbs->destroy_connector)(mgr, port->connector);
	870	+
	871	+ /* we can't destroy the connector here, as
	872	+ we might be holding the mode_config.mutex
	873	+ from an EDID retrieval */
	874	+ if (port->connector) {
	875	+ mutex_lock(&mgr->destroy_connector_lock);
	876	+ list_add(&port->connector->destroy_list, &mgr->destroy_connector_list);
	877	+ mutex_unlock(&mgr->destroy_connector_lock);
	878	+ schedule_work(&mgr->destroy_connector_work);
	879	+ }
872	880	drm_dp_port_teardown_pdt(port, port->pdt);
873	881
874	882	if (!port->input && port->vcpi.vcpi > 0)
@@ -2649,6 +2657,30 @@ static void drm_dp_tx_work(struct work_struct *work) · 1774 unmodified lines
2649	2657	mutex_unlock(&mgr->qlock);
2650	2658	}
2651	2659
	2660	+static void drm_dp_destroy_connector_work(struct work_struct *work)
	2661	+{
	2662	+ struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, destroy_connector_work);
	2663	+ struct drm_connector *connector;
	2664	+
	2665	+ /*
	2666	+ * Not a regular list traverse as we have to drop the destroy
	2667	+ * connector lock before destroying the connector, to avoid AB->BA
	2668	+ * ordering between this lock and the config mutex.
	2669	+ */
	2670	+ for (;;) {
	2671	+ mutex_lock(&mgr->destroy_connector_lock);
	2672	+ connector = list_first_entry_or_null(&mgr->destroy_connector_list, struct drm_connector, destroy_list);
	2673	+ if (!connector) {
	2674	+ mutex_unlock(&mgr->destroy_connector_lock);
	2675	+ break;
	2676	+ }
	2677	+ list_del(&connector->destroy_list);
	2678	+ mutex_unlock(&mgr->destroy_connector_lock);
	2679	+
	2680	+ mgr->cbs->destroy_connector(mgr, connector);
	2681	+ }
	2682	+}
	2683	+
2652	2684	/**
2653	2685	* drm_dp_mst_topology_mgr_init - initialise a topology manager
2654	2686	* @mgr: manager struct to initialise
@@ -2668,10 +2700,13 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr, · 13 unmodified lines
2668	2700	mutex_init(&mgr->lock);
2669	2701	mutex_init(&mgr->qlock);
2670	2702	mutex_init(&mgr->payload_lock);
	2703	+ mutex_init(&mgr->destroy_connector_lock);
2671	2704	INIT_LIST_HEAD(&mgr->tx_msg_upq);
2672	2705	INIT_LIST_HEAD(&mgr->tx_msg_downq);
	2706	+ INIT_LIST_HEAD(&mgr->destroy_connector_list);
2673	2707	INIT_WORK(&mgr->work, drm_dp_mst_link_probe_work);
2674	2708	INIT_WORK(&mgr->tx_work, drm_dp_tx_work);
	2709	+ INIT_WORK(&mgr->destroy_connector_work, drm_dp_destroy_connector_work);
2675	2710	init_waitqueue_head(&mgr->tx_waitq);
2676	2711	mgr->dev = dev;
2677	2712	mgr->aux = aux;
@@ -2696,6 +2731,7 @@ EXPORT_SYMBOL(drm_dp_mst_topology_mgr_init); · 18 unmodified lines
2696	2731	*/
2697	2732	void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr)
2698	2733	{
	2734	+ flush_work(&mgr->destroy_connector_work);
2699	2735	mutex_lock(&mgr->payload_lock);
2700	2736	kfree(mgr->payloads);
2701	2737	mgr->payloads = NULL;

include/drm/drm_crtc.h+2−0

@@ -743,6 +743,8 @@ struct drm_connector { · 742 unmodified lines
743	743	uint8_t num_h_tile, num_v_tile;
744	744	uint8_t tile_h_loc, tile_v_loc;
745	745	uint16_t tile_h_size, tile_v_size;
	746	+
	747	+ struct list_head destroy_list;
746	748	};
747	749
748	750	/**

include/drm/drm_dp_mst_helper.h+4−0

@@ -463,6 +463,10 @@ struct drm_dp_mst_topology_mgr { · 462 unmodified lines
463	463	struct work_struct work;
464	464
465	465	struct work_struct tx_work;
	466	+
	467	+ struct list_head destroy_connector_list;
	468	+ struct mutex destroy_connector_lock;
	469	+ struct work_struct destroy_connector_work;
466	470	};
467	471
468	472	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);