From 6b8eeca65b18ae77e175cc2b6571731f0ee413bf Mon Sep 17 00:00:00 2001 From: Dave Airlie Date: Mon, 15 Jun 2015 10:34:28 +1000 Subject: [PATCH] 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 Cc: stable@vger.kernel.org Signed-off-by: Dave Airlie --- drivers/gpu/drm/drm_dp_mst_topology.c | 40 +++++++++++++++++++++++++++++++++-- include/drm/drm_crtc.h | 2 ++ include/drm/drm_dp_mst_helper.h | 4 ++++ 3 files changed, 44 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index f721349..778bbb6 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -867,8 +867,16 @@ static void drm_dp_destroy_port(struct kref *kref) port->vcpi.num_slots = 0; kfree(port->cached_edid); - if (port->connector) - (*port->mgr->cbs->destroy_connector)(mgr, port->connector); + + /* we can't destroy the connector here, as + we might be holding the mode_config.mutex + from an EDID retrieval */ + if (port->connector) { + mutex_lock(&mgr->destroy_connector_lock); + list_add(&port->connector->destroy_list, &mgr->destroy_connector_list); + mutex_unlock(&mgr->destroy_connector_lock); + schedule_work(&mgr->destroy_connector_work); + } drm_dp_port_teardown_pdt(port, port->pdt); if (!port->input && port->vcpi.vcpi > 0) @@ -2649,6 +2657,30 @@ static void drm_dp_tx_work(struct work_struct *work) mutex_unlock(&mgr->qlock); } +static void drm_dp_destroy_connector_work(struct work_struct *work) +{ + struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, destroy_connector_work); + struct drm_connector *connector; + + /* + * Not a regular list traverse as we have to drop the destroy + * connector lock before destroying the connector, to avoid AB->BA + * ordering between this lock and the config mutex. + */ + for (;;) { + mutex_lock(&mgr->destroy_connector_lock); + connector = list_first_entry_or_null(&mgr->destroy_connector_list, struct drm_connector, destroy_list); + if (!connector) { + mutex_unlock(&mgr->destroy_connector_lock); + break; + } + list_del(&connector->destroy_list); + mutex_unlock(&mgr->destroy_connector_lock); + + mgr->cbs->destroy_connector(mgr, connector); + } +} + /** * drm_dp_mst_topology_mgr_init - initialise a topology manager * @mgr: manager struct to initialise @@ -2668,10 +2700,13 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr, mutex_init(&mgr->lock); mutex_init(&mgr->qlock); mutex_init(&mgr->payload_lock); + mutex_init(&mgr->destroy_connector_lock); INIT_LIST_HEAD(&mgr->tx_msg_upq); INIT_LIST_HEAD(&mgr->tx_msg_downq); + INIT_LIST_HEAD(&mgr->destroy_connector_list); INIT_WORK(&mgr->work, drm_dp_mst_link_probe_work); INIT_WORK(&mgr->tx_work, drm_dp_tx_work); + INIT_WORK(&mgr->destroy_connector_work, drm_dp_destroy_connector_work); init_waitqueue_head(&mgr->tx_waitq); mgr->dev = dev; mgr->aux = aux; @@ -2696,6 +2731,7 @@ EXPORT_SYMBOL(drm_dp_mst_topology_mgr_init); */ void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr) { + flush_work(&mgr->destroy_connector_work); mutex_lock(&mgr->payload_lock); kfree(mgr->payloads); mgr->payloads = NULL; 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); -- 2.7.4