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

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Date:   Fri, 27 Jan 2023 09:15:08 +0200
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Alexander Duyck <alexander.duyck@...il.com>, nbd@....name,
        davem@...emloft.net, edumazet@...gle.com, hawk@...nel.org,
        linux-kernel@...r.kernel.org, linyunsheng@...wei.com,
        lorenzo@...nel.org, netdev@...r.kernel.org, pabeni@...hat.com
Subject: Re: [net PATCH] skb: Do mix page pool and page referenced frags in GRO

Thanks Alexander!

On Fri, 27 Jan 2023 at 01:13, Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 26 Jan 2023 11:06:59 -0800 Alexander Duyck wrote:
> > From: Alexander Duyck <alexanderduyck@...com>
> >
> > 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@....name>
> > Signed-off-by: Alexander Duyck <alexanderduyck@...com>
>
> 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.
>
> > diff --git a/net/core/gro.c b/net/core/gro.c
> > index 506f83d715f8..4bac7ea6e025 100644
> > --- a/net/core/gro.c
> > +++ b/net/core/gro.c
> > @@ -162,6 +162,15 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
> >       struct sk_buff *lp;
> >       int segs;
> >
> > +     /* Do not splice page pool based packets w/ non-page pool
> > +      * packets. This can result in reference count issues as page
> > +      * pool pages will not decrement the reference count and will
> > +      * instead be immediately returned to the pool or have frag
> > +      * count decremented.
> > +      */
> > +     if (p->pp_recycle != skb->pp_recycle)
> > +             return -ETOOMANYREFS;
> >
> >       /* pairs with WRITE_ONCE() in netif_set_gro_max_size() */
> >       gro_max_size = READ_ONCE(p->dev->gro_max_size);
> >
> >
> >
>
Acked-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>