drm/dp_mst: Fix flushing the delayed port/mstb destroy work

Atm, a pending delayed destroy work during module removal will be
canceled, leaving behind MST ports, mstbs. Fix this by using a dedicated
workqueue which will be drained of requeued items as well when
destroying it.

v2:
- Check if wq is NULL before calling destroy_workqueue().

Cc: Lyude Paul <lyude@redhat.com>
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200610134704.25270-1-imre.deak@intel.com

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 8ff4caf..104f979 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1630,7 +1630,7 @@ static void drm_dp_destroy_mst_branch_device(struct kref *kref)
        mutex_lock(&mgr->delayed_destroy_lock);
        list_add(&mstb->destroy_next, &mgr->destroy_branch_device_list);
        mutex_unlock(&mgr->delayed_destroy_lock);
-       schedule_work(&mgr->delayed_destroy_work);
+       queue_work(mgr->delayed_destroy_wq, &mgr->delayed_destroy_work);
 }
 
 /**
@@ -1747,7 +1747,7 @@ static void drm_dp_destroy_port(struct kref *kref)
        mutex_lock(&mgr->delayed_destroy_lock);
        list_add(&port->next, &mgr->destroy_port_list);
        mutex_unlock(&mgr->delayed_destroy_lock);
-       schedule_work(&mgr->delayed_destroy_work);
+       queue_work(mgr->delayed_destroy_wq, &mgr->delayed_destroy_work);
 }
 
 /**
@@ -5203,6 +5203,15 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
        INIT_LIST_HEAD(&mgr->destroy_port_list);
        INIT_LIST_HEAD(&mgr->destroy_branch_device_list);
        INIT_LIST_HEAD(&mgr->up_req_list);
+
+       /*
+        * delayed_destroy_work will be queued on a dedicated WQ, so that any
+        * requeuing will be also flushed when deiniting the topology manager.
+        */
+       mgr->delayed_destroy_wq = alloc_ordered_workqueue("drm_dp_mst_wq", 0);
+       if (mgr->delayed_destroy_wq == NULL)
+               return -ENOMEM;
+
        INIT_WORK(&mgr->work, drm_dp_mst_link_probe_work);
        INIT_WORK(&mgr->tx_work, drm_dp_tx_work);
        INIT_WORK(&mgr->delayed_destroy_work, drm_dp_delayed_destroy_work);
@@ -5247,7 +5256,11 @@ void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr)
 {
        drm_dp_mst_topology_mgr_set_mst(mgr, false);
        flush_work(&mgr->work);
-       cancel_work_sync(&mgr->delayed_destroy_work);
+       /* The following will also drain any requeued work on the WQ. */
+       if (mgr->delayed_destroy_wq) {
+               destroy_workqueue(mgr->delayed_destroy_wq);
+               mgr->delayed_destroy_wq = NULL;
+       }
        mutex_lock(&mgr->payload_lock);
        kfree(mgr->payloads);
        mgr->payloads = NULL;

diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index b230ff6..8b9eb4d 100644 (file)
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -681,6 +681,14 @@ struct drm_dp_mst_topology_mgr {
         * @destroy_branch_device_list.
         */
        struct mutex delayed_destroy_lock;
+
+       /**
+        * @delayed_destroy_wq: Workqueue used for delayed_destroy_work items.
+        * A dedicated WQ makes it possible to drain any requeued work items
+        * on it.
+        */
+       struct workqueue_struct *delayed_destroy_wq;
+
        /**
         * @delayed_destroy_work: Work item to destroy MST port and branch
         * devices, needed to avoid locking inversion.