[Intel-wired-lan] [PATCH net-queue v1] igc: Fix trying to register an already registered xdp_rxq

[Alexander Lobakin <alexandr.lobakin@intel.com>]

From: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Date: Wed, 12 Jan 2022 16:40:15 -0800

> When changing the number of RX descriptors, for example, by doing
> 
>  $ ethtool -G enp3s0 rx 1024
> 
> the XDP RX queue information (xdp_rxq) may be already registered, if
> it's registered there's no need to do any thing in relation to
> xdp_rxq, none of it's parameters will change if we change the number
> of descriptors, for example.
> 
> Fixes: 4609ffb9f615 ("igc: Refactor XDP rxq info registration")
> Reported-by: Lennert Buytenhek <buytenh@wantstofly.org>
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
> ---
> Lennert, I added your name and email to the Reported-by tag, please
> see if you are ok with it.
> 
>  drivers/net/ethernet/intel/igc/igc_main.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> index e29aadbc6744..d163139161fc 100644
> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> @@ -1,6 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>  /* Copyright (c)  2018 Intel Corporation */
>  
> +#include "net/xdp.h"
>  #include <linux/module.h>
>  #include <linux/types.h>
>  #include <linux/if_vlan.h>
> @@ -499,12 +500,14 @@ 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;
> +	if (!xdp_rxq_info_is_reg(&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;
> +		}
>  	}

While the fix itself is correct, I don't really like the setup flow
in igc_ethtool_set_ringparam() (here: [0]).

Instead of unregistering/freeing Rx rings at first and then
allocating/registering the new ones, driver registers the new ones
at first and then unregister the olds.
It may cause other issues apart from this one. E.g. driver performs
Rxq info unregistering at the end, so netdevice may end up with no
Rxq info registered after changing the number of descriptors (Rxq
info is enumerated by queue index).

To me, the righteous approach would be changing this flow to more
common, i.e. do unregistering/freeing at first and then register
and allocate.

>  
>  	size = sizeof(struct igc_rx_buffer) * rx_ring->count;
> -- 
> 2.34.1

[0] https://elixir.bootlin.com/linux/latest/source/drivers/net/ethernet/intel/igc/igc_ethtool.c#L664

Thanks,
Al