On Mon, 15 Jun 2015, Dave Airlie airlied@gmail.com wrote:
From: Dave Airlie airlied@redhat.com
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.
Signed-off-by: Dave Airlie airlied@redhat.com
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 a88ae51..c98c96d 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -871,8 +871,16 @@ 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 destroy the connector here, as
we *can't* ?
BR, Jani.
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)
@@ -2652,6 +2660,30 @@ 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
@@ -2671,10 +2703,13 @@ 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;
@@ -2699,6 +2734,7 @@ 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 ca71c03..5423358 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -731,6 +731,8 @@ 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 04e668a..4786919 100644 --- a/include/drm/drm_dp_mst_helper.h +++ b/include/drm/drm_dp_mst_helper.h @@ -464,6 +464,10 @@ 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);
2.4.1
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