Re: [PATCH net 1/1] ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()

[Ido Schimmel <idosch@nvidia.com>]

On Fri, Aug 07, 2026 at 10:31:29AM +0200, Paolo Abeni wrote:
> My my concern is against possible regressions. At this late stage of the
> release cycle we want to avoid them, even if there are already similar
> pre-existing bugs.
> 
> AFAICS pktgen sets the per pkt_gen device F_SHARED flag unconditionally
> and push shared skbs when F_SHARED is set regardless the NIC priv_flags.
> 
> What about addressing both issues in the same series? Something like
> the following (completely untested) would do:

I don't have time to look into pktgen right now. I disagree with
conditioning the merging of this fix - which makes IPv6 tunnels
consistent with existing ones - on fixing a benchmarking / testing
module that is not available to unprivileged users.

> ---
> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
> index ee64f3012321..a7126d639586 100644
> --- a/net/core/pktgen.c
> +++ b/net/core/pktgen.c
> @@ -1385,6 +1385,9 @@ static ssize_t pktgen_if_write(struct file *file,
>  					return -EINVAL;
>  				pkt_dev->flags &= ~flag;
>  			} else {
> +				if (!(pkt_dev->odev->priv_flags &
> +				      IFF_TX_SKB_SHARING))
> +					return -EINVAL;
>  				pkt_dev->flags |= flag;

Doesn't this reject the enablement of any flag (not just "SHARED") on a
device that doesn't advertise IFF_TX_SKB_SHARING?

>  			}
>  
> @@ -3868,13 +3871,15 @@ static int pktgen_add_device(struct pktgen_thread *t, const char *ifname)
>  	pkt_dev->svlan_id = 0xffff;
>  	pkt_dev->burst = 1;
>  	pkt_dev->node = NUMA_NO_NODE;
> -	pkt_dev->flags = F_SHARED;	/* SKB shared by default */
> +	pkt_dev->flags = 0;
>  
>  	err = pktgen_setup_dev(t->net, pkt_dev, ifname);
>  	if (err)
>  		goto out1;
> -	if (pkt_dev->odev->priv_flags & IFF_TX_SKB_SHARING)
> +	if (pkt_dev->odev->priv_flags & IFF_TX_SKB_SHARING) {
>  		pkt_dev->clone_skb = pg_clone_skb_d;
> +		pkt_dev->flags |= F_SHARED;
> +	}
>  
>  	pkt_dev->entry = proc_create_data(ifname, 0600, t->net->proc_dir,
>  					  &pktgen_if_proc_ops, pkt_dev);
> ---
> 
> /P
>