Re: [PATCH net-next 10/10] net/mlx5e: Enable the data direct netdev feature

[Mina Almasry <almasrymina@google.com>]

On Thu, Oct 8, 2026 at 6:28 AM Tariq Toukan <tariqt@nvidia.com> wrote:
> From: Dragos Tatulea <dtatulea@nvidia.com>
>
> +	/* Changing the flag reopens the channels with a different DMA device,
> +	 * which would break any dmabuf currently bound to this netdev.
> +	 */
> +	if (netdev_has_dmabuf_binding(netdev, NULL)) {
> +		netdev_err(netdev, "Can't change data_direct while dmabufs are bound\n");
> +		return -EBUSY;
> +	}
> +
> +	new_params = priv->channels.params;
> +	MLX5E_SET_PFLAG(&new_params, MLX5E_PFLAG_DATA_DIRECT, enable);
> +
> +	return mlx5e_safe_switch_params(priv, &new_params, NULL, NULL, true);

(Note: LLM-assisted review comment below.)

set_pflag_data_direct() is called under rtnl_lock() only, whereas
netdev_nl_bind_rx_doit() and netdev_nl_bind_tx_doit() serialize bindings under
netdev_lock(netdev) without holding rtnl_lock().

Should set_pflag_data_direct() hold netdev_lock(netdev) across both
netdev_has_dmabuf_binding() and mlx5e_safe_switch_params() (just as
mlx5e_data_direct_event() does in patch 08/10) so a concurrent bind-rx/bind-tx
cannot race past the -EBUSY check while channels are switching DMA devices?

-- 
Thanks,
Mina