From: Dave Airlie <airlied@xxxxxxxxxx>
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@xxxxxxxxxx>
---
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 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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