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Message-Id: <1437008972-9140-164-git-send-email-kamal@canonical.com>
Date: Wed, 15 Jul 2015 18:08:04 -0700
From: Kamal Mostafa <kamal@...onical.com>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
kernel-team@...ts.ubuntu.com
Cc: Dave Airlie <airlied@...hat.com>,
Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 163/251] drm/dp/mst: close deadlock in connector destruction.
3.19.8-ckt4 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Dave Airlie <airlied@...hat.com>
commit 6b8eeca65b18ae77e175cc2b6571731f0ee413bf upstream.
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 <daniel.vetter@...ll.ch>
Signed-off-by: Dave Airlie <airlied@...hat.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.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 4d7a4d9..30308ab 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -863,8 +863,16 @@ 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)
@@ -2631,6 +2639,30 @@ 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
@@ -2650,10 +2682,13 @@ 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;
@@ -2678,6 +2713,7 @@ 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 b863298..3dab77c 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -689,6 +689,8 @@ 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 00c1da9..180f8a3 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);
--
1.9.1
--
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