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

On Thu, Aug 6, 2026 at 4:52 PM Ido Schimmel <[email protected]> wrote:
>
> On Wed, Aug 05, 2026 at 05:29:02PM -0700, Jakub Kicinski wrote:
> > On Wed, 5 Aug 2026 12:07:21 +0300 Ido Schimmel wrote:
> > > __gre6_xmit() and ip6erspan_tunnel_xmit() already call skb_cow_head()
> > > before calling ip6_tnl_xmit().
> >
> > Probably just me but can't they all be buggy?
> > PKTGEN likes to send shared skbs around in funny ways.
> > Can we get a good explanation in the commit msg or maybe let's
> > keep the check?
>
> ip6_tnl_xmit() is accessible via two Ethernet devices (pktgen doesn't
> support other types) and they both clear IFF_TX_SKB_SHARING, so if
> pktgen sends them shared skbs, I would say that it's a pktgen bug and
> not a reason to block this patch. Note that pktgen is not available to
> unprivileged users, so it's a less severe bug.
>
> The patch also makes ip6_tnl_xmit() consistent with its IPv4 counterpart
> (ip_tunnel_xmit()) which is already using skb_cow_head().
>
> Zhiling, please add a note in the commit message that ip6gretap and
> ip6erspan do not expect to be handed shared skbs given that they clear
> IFF_TX_SKB_SHARING.

Thanks, Ido. I'll add a note to the commit message explaining that
ip6gretap and ip6erspan clear IFF_TX_SKB_SHARING and therefore do not
expect shared skbs, and send a v2 with your Reviewed-by tag retained.