On Mon, 15 Jun 2015, Dave Airlie <airlied@xxxxxxxxx> wrote:
> 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 *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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--
Jani Nikula, Intel Open Source Technology Center
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