FAILED: patch "[PATCH] vdpa/mlx5: Avoid processing works if workqueue was destroyed" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ad6dc1daaf29f97f23cc810d60ee01c0e83f4c6b Mon Sep 17 00:00:00 2001
From: Eli Cohen <[email protected]>
Date: Mon, 21 Mar 2022 16:13:03 +0200
Subject: [PATCH] vdpa/mlx5: Avoid processing works if workqueue was destroyed

If mlx5_vdpa gets unloaded while a VM is running, the workqueue will be destroyed. However, vhost might still have reference to the kick function and might attempt to push new works. This could lead to null pointer dereference.

To fix this, set mvdev->wq to NULL just before destroying and verify that the workqueue is not NULL in mlx5_vdpa_kick_vq before attempting to push a new work.

index c0f0ecb82c6f..2f4fb09f1e89 100644
@@ -1712,7 +1712,7 @@ static void mlx5_vdpa_kick_vq(struct vdpa_device *vdev, u16 idx)
 		return;
 
 	if (unlikely(is_ctrl_vq_idx(mvdev, idx))) {
-		if (!mvdev->cvq.ready)
+		if (!mvdev->wq || !mvdev->cvq.ready)
 			return;
 
 		wqent = kzalloc(sizeof(*wqent), GFP_ATOMIC);

@@ -2779,9 +2779,12 @@ static void mlx5_vdpa_dev_del(struct vdpa_mgmt_dev *v_mdev, struct vdpa_device *
 	struct mlx5_vdpa_mgmtdev *mgtdev = container_of(v_mdev, struct mlx5_vdpa_mgmtdev, mgtdev);
 	struct mlx5_vdpa_dev *mvdev = to_mvdev(dev);
 	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
+	struct workqueue_struct *wq;
 
 	mlx5_notifier_unregister(mvdev->mdev, &ndev->nb);
-	destroy_workqueue(mvdev->wq);
+	wq = mvdev->wq;
+	mvdev->wq = NULL;
+	destroy_workqueue(wq);
 	_vdpa_unregister_device(dev);
 	mgtdev->ndev = NULL;
 }