Subject: Re: [PATCH 1/2 net-next v3] igc: avoid kernel warning when changing RX ring parameters

From: Vinicius Costa Gomes <[email-masked]>
Date: Fri, 14 Jan 2022 11:10:29 -0800

Corinna Vinschen <[email-masked]> writes:

> Calling ethtool changing the RX ring parameters like this:
>
>   $ ethtool -G eth0 rx 1024
>
> on igc triggers the "Missing unregister, handled but fix driver" warning in
> xdp_rxq_info_reg().
>
> igc_ethtool_set_ringparam() copies the igc_ring structure but neglects to
> reset the xdp_rxq_info member before calling igc_setup_rx_resources().
> This in turn calls xdp_rxq_info_reg() with an already registered xdp_rxq_info.
>
> Make sure to unregister the xdp_rxq_info structure first in
> igc_setup_rx_resources.  Move xdp_rxq_info handling down to bethe last
> action, thus allowing to remove the xdp_rxq_info_unreg call in the error path.
>
> Fixes: 73f1071c1d29 ("igc: Add support for XDP_TX action")
> Signed-off-by: Corinna Vinschen <[email-masked]>
> ---
>  drivers/net/ethernet/intel/igc/igc_main.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> index 2f17f36e94fd..97144f6db36e 100644
> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> @@ -505,14 +505,6 @@ int igc_setup_rx_resources(struct igc_ring *rx_ring)
>  	u8 index = rx_ring->queue_index;
>  	int size, desc_len, res;
>  
> -	res = xdp_rxq_info_reg(&rx_ring->xdp_rxq, ndev, index,
> -			       rx_ring->q_vector->napi.napi_id);
> -	if (res < 0) {
> -		netdev_err(ndev, "Failed to register xdp_rxq index %u\n",
> -			   index);
> -		return res;
> -	}
> -
>  	size = sizeof(struct igc_rx_buffer) * rx_ring->count;
>  	rx_ring->rx_buffer_info = vzalloc(size);
>  	if (!rx_ring->rx_buffer_info)
> @@ -534,10 +526,20 @@ int igc_setup_rx_resources(struct igc_ring *rx_ring)
>  	rx_ring->next_to_clean = 0;
>  	rx_ring->next_to_use = 0;
>  
> +	/* XDP RX-queue info */
> +	if (xdp_rxq_info_is_reg(&rx_ring->xdp_rxq))
> +		xdp_rxq_info_unreg(&rx_ring->xdp_rxq);
> +	res = xdp_rxq_info_reg(&rx_ring->xdp_rxq, ndev, index,
> +			       rx_ring->q_vector->napi.napi_id);
> +	if (res < 0) {
> +		netdev_err(ndev, "Failed to register xdp_rxq index %u\n",
> +			   index);
> +		return res;

Here and in the igb patch, it should be 'goto err', no?

Another suggestion is to add the warning that Lennert reported in the
commit message (the comment from Maciej in that other thread).

Apart from that, I think this is cleaner than what I had proposed.

Cheers,
-- 
Vinicius