Re: [PATCH net v2] net: gro: avoid nesting TCP GSO skbs in skb_gro_receive_list()

On Thu, Jul 23, 2026 at 3:39 PM Jakub Kicinski <[email protected]> wrote:
>
> On Thu, 23 Jul 2026 17:16:01 +0800 [email protected] wrote:
> > From: HW He <[email protected]>
> >
> > On devices that support both NETIF_F_GRO_HW and NETIF_F_GRO_FRAGLIST,
>
> "devices that support FRAGLIST"? Isn't it a software feature?
>
> > the hardware or driver may deliver packets that have already been
>
> If you have a driver in mind please name it.
>
> > aggregated into a TCP GSO skb with frags[]. GRO may then
> > aggregate the skb again in skb_gro_receive_list().
> >
> > This can create a nested GSO skb, which is not handled correctly by the
> > later GSO segmentation paths. When the skb is segmented by
> > skb_segment_list(), it not be fully restored to the original packets.
> >
> > Avoid this by setting NAPI_GRO_CB(skb)->flush for GSO skbs before
> > aggregation.
>
> I don't think we can do this. For GRO_HW devices re-aggregating
> in SW is quite helpful, HW often runs out of contexts or times
> out too soon, generating skbs with 16kB..32kB of data, the SW
> can help bring it up to full TSO.

Also, after e751256486d0 ("net: gro: fix double aggregation of
flush-marked skbs"), it's not clear an another bug remains.

If it is: as said "nested GRO" of hw + sw GRO is intentional, e.g., for BIG-TCP.

But it may not be anticipated for skb_gro_receive_list. One option
would be to skip the fraglist GSO optimization for such packets.

First I'd like to understand better what exact bug remains.