Re: [Intel-wired-lan] [PATCH net-next v2] ixgbe: XDP: fix checker warning from rcu pointer

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Tue, Nov 22, 2022 at 03:48:25PM -0800, Jesse Brandeburg wrote:
> The ixgbe driver uses an older style failure mode when initializing the
> XDP program and the queues. It causes some warnings when running C=2
> checking builds (and it's the last one in the ethernet/intel tree).
> 
> $ make W=1 C=2 M=`pwd`/drivers/net/ethernet/intel modules
> .../ixgbe_main.c:10301:25: error: incompatible types in comparison expression (different address spaces):
> .../ixgbe_main.c:10301:25:    struct bpf_prog [noderef] __rcu *
> .../ixgbe_main.c:10301:25:    struct bpf_prog *
> 
> Fix the problem by removing the line that tried to re-xchg "the old_prog
> pointer" if there was an error, to make this driver act like the other
> drivers which return the error code without "pointer restoration."
> 
> Also, update the "copy the pointer" logic to use WRITE_ONCE as many/all
> the other drivers do, which required making a change in two separate
> functions that write the xdp_prog variable in the ring.
> 
> The code here was modeled after the code in i40e/i40e_xdp_setup().
> 
> NOTE: Compile-tested only.

Giving samples/bpf/xdp1 a spin wouldn't hurt :P

Otherwise, this LGTM, shouldn't break anything:
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>

> 
> CC: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> CC: Magnus Karlsson <magnus.karlsson@intel.com>
> Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index ab8370c413f3..93699d2ae051 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -6647,7 +6647,7 @@ int ixgbe_setup_rx_resources(struct ixgbe_adapter *adapter,
>  			     rx_ring->queue_index, ixgbe_rx_napi_id(rx_ring)) < 0)
>  		goto err;
>  
> -	rx_ring->xdp_prog = adapter->xdp_prog;
> +	WRITE_ONCE(rx_ring->xdp_prog, adapter->xdp_prog);
>  
>  	return 0;
>  err:
> @@ -10297,14 +10297,13 @@ static int ixgbe_xdp_setup(struct net_device *dev, struct bpf_prog *prog)
>  			synchronize_rcu();
>  		err = ixgbe_setup_tc(dev, adapter->hw_tcs);
>  
> -		if (err) {
> -			rcu_assign_pointer(adapter->xdp_prog, old_prog);
> +		if (err)
>  			return -EINVAL;
> -		}
>  	} else {
> -		for (i = 0; i < adapter->num_rx_queues; i++)
> -			(void)xchg(&adapter->rx_ring[i]->xdp_prog,
> -			    adapter->xdp_prog);
> +		for (i = 0; i < adapter->num_rx_queues; i++) {
> +			WRITE_ONCE(adapter->rx_ring[i]->xdp_prog,
> +				   adapter->xdp_prog);
> +		}
>  	}
>  
>  	if (old_prog)
> 
> base-commit: 50ae3afd446667c6fe540f41b84ff83172c38b27
> -- 
> 2.31.1
> 
_______________________________________________
Intel-wired-lan mailing list
Intel-wired-lan@osuosl.org
https://lists.osuosl.org/mailman/listinfo/intel-wired-lan