From: Eli Cohen <elic@nvidia.com>
Date: Mon, 21 Mar 2022 16:13:03 +0200
Subject: vdpa/mlx5: Avoid processing works if workqueue was destroyed
Patch-mainline: v5.18-rc1
Git-commit: ad6dc1daaf29f97f23cc810d60ee01c0e83f4c6b
References: jsc#PED-1549

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.

Fixes: 5262912ef3cf ("vdpa/mlx5: Add support for control VQ and MAC setting")
Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20220321141303.9586-1-elic@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -1712,7 +1712,7 @@ static void mlx5_vdpa_kick_vq(struct vdp
 		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 vdp
 	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;
 }