Re: [PATCH] sfc: siena: handle NULL returned by xdp_convert_buff_to_frame()

[Simon Horman <horms@kernel.org>]

On Tue, Jul 22, 2025 at 07:32:30PM -0500, Chenyuan Yang wrote:
> The xdp_convert_buff_to_frame() function can return NULL when there is
> insufficient headroom in the buffer to store the xdp_frame structure
> or when the driver didn't reserve enough tailroom for skb_shared_info.
> 
> Currently, the sfc siena driver does not check for this NULL return value
> in the XDP_TX case within efx_do_xdp().
> 
> Fix by adding a proper NULL check in the XDP_TX case. If conversion
> fails, free the RX buffer and increment the bad drops counter, following
> the same pattern used for other XDP error conditions in this driver.
> 
> Signed-off-by: Chenyuan Yang <chenyuan0y@gmail.com>
> Fixes: d48523cb88e0 ("sfc: Copy shared files needed for Siena (part 2)")
> ---
>  drivers/net/ethernet/sfc/siena/rx.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/ethernet/sfc/siena/rx.c b/drivers/net/ethernet/sfc/siena/rx.c
> index 98d3c0743c0f..65f6daad3168 100644
> --- a/drivers/net/ethernet/sfc/siena/rx.c
> +++ b/drivers/net/ethernet/sfc/siena/rx.c
> @@ -310,6 +310,12 @@ static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel,
>  	case XDP_TX:
>  		/* Buffer ownership passes to tx on success. */
>  		xdpf = xdp_convert_buff_to_frame(&xdp);
> +		if (unlikely(!xdpf)) {
> +			efx_siena_free_rx_buffers(rx_queue, rx_buf, 1);
> +			channel->n_rx_xdp_bad_drops++;
> +			break;
> +		}

I see the incidence of this cleanup code multiplying in this function.
I would be nice to follow-up by consolidating that - I'd suggest
in the form of a goto label at the end of the function.

But as a fix for net this minimal patch seems appropriate to me.

Reviewed-by: Simon Horman <horms@kernel.org>

> +
>  		err = efx_siena_xdp_tx_buffers(efx, 1, &xdpf, true);
>  		if (unlikely(err != 1)) {
>  			efx_siena_free_rx_buffers(rx_queue, rx_buf, 1);
> -- 
> 2.34.1
> 
>