virtio_net: Add a lock for the command VQ.

The command VQ will no longer be protected by the RTNL lock. Use a
mutex to protect the control buffer header and the VQ.
Signed-off-by: Daniel Jurgens <danielj@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Heng Qi <hengqi@linux.alibaba.com>
Tested-by: Heng Qi <hengqi@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/virtio_net.c

@@ -411,6 +411,9 @@ struct virtnet_info {
 	/* Has control virtqueue */
 	bool has_cvq;
 
+	/* Lock to protect the control VQ */
+	struct mutex cvq_lock;
+
 	/* Host can handle any s/g split between our header and packet data */
 	bool any_header_sg;
 
@@ -2675,6 +2678,7 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
 	/* Caller should know better */
 	BUG_ON(!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ));
 
+	mutex_lock(&vi->cvq_lock);
 	vi->ctrl->status = ~0;
 	vi->ctrl->hdr.class = class;
 	vi->ctrl->hdr.cmd = cmd;
@@ -2697,11 +2701,12 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
 	if (ret < 0) {
 		dev_warn(&vi->vdev->dev,
 			 "Failed to add sgs for command vq: %d\n.", ret);
+		mutex_unlock(&vi->cvq_lock);
 		return false;
 	}
 
 	if (unlikely(!virtqueue_kick(vi->cvq)))
-		return vi->ctrl->status == VIRTIO_NET_OK;
+		goto unlock;
 
 	/* Spin for a response, the kick causes an ioport write, trapping
 	 * into the hypervisor, so the request should be handled immediately.
@@ -2712,6 +2717,8 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
 		cpu_relax();
 	}
 
+unlock:
+	mutex_unlock(&vi->cvq_lock);
 	return vi->ctrl->status == VIRTIO_NET_OK;
 }
 
@@ -5736,6 +5743,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
 		vi->has_cvq = true;
 
+	mutex_init(&vi->cvq_lock);
+
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) {
 		mtu = virtio_cread16(vdev,
 				     offsetof(struct virtio_net_config,