Re: [net PATCH] skb: Do mix page pool and page referenced frags in GRO

[Jesper Dangaard Brouer]

On 27/01/2023 00.13, Jakub Kicinski wrote:
> On Thu, 26 Jan 2023 11:06:59 -0800 Alexander Duyck wrote:
> > From: Alexander Duyck<alexanderduyck@xxxxxx>
> >
> > GSO should not merge page pool recycled frames with standard reference
> > counted frames. Traditionally this didn't occur, at least not often.
> > However as we start looking at adding support for wireless adapters there
> > becomes the potential to mix the two due to A-MSDU repartitioning frames in
> > the receive path. There are possibly other places where this may have
> > occurred however I suspect they must be few and far between as we have not
> > seen this issue until now.
> >
> > Fixes: 53e0961da1c7 ("page_pool: add frag page recycling support in page pool")
> > Reported-by: Felix Fietkau<nbd@xxxxxxxx>
> > Signed-off-by: Alexander Duyck<alexanderduyck@xxxxxx>
> Exciting investigation!
> Felix, out of curiosity - the impact of loosing GRO on performance is
> not significant enough to care?  We could possibly try to switch to
> using the frag list if we can't merge into frags safely.

Using the frag list sounds scary, because we recently learned that
kfree_skb_list requires all SKBs on the list to have same refcnt (else
the walking of the list can lead to other bugs).

--Jesper