Re: [PATCH 3/3] drm/dp_mst: Fix flushing the delayed port/mstb destroy work

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Mon, Jun 08, 2020 at 12:25:22AM +0300, Imre Deak wrote:
> 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.
>

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
 
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 17 ++++++++++++++---
>  include/drm/drm_dp_mst_helper.h       |  8 ++++++++
>  2 files changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 083255c33ee0..075fb5ac9264 100644
> --- 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);
>  }
>  
>  /**
> @@ -5208,6 +5208,15 @@ 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);
> @@ -5252,7 +5261,9 @@ 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. */
> +	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 b230ff6f7081..8b9eb4db3381 100644
> --- 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.
> -- 
> 2.23.1
> 
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