linux-kernel - Re: [PATCH net] veth: Fix RX stats for bpf_redirect

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Message-ID: <20231028231135.GA2236124@n191-129-154.byted.org>
Date:   Sat, 28 Oct 2023 23:11:37 +0000
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Peilin Ye <peilin.ye@...edance.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Cong Wang <cong.wang@...edance.com>,
        Jiang Wang <jiang.wang@...edance.com>,
        Youlun Zhang <zhangyoulun@...edance.com>
Subject: Re: [PATCH net] veth: Fix RX stats for bpf_redirect_peer() traffic

Hi Daniel,

Thanks for taking a look!

On Sat, Oct 28, 2023 at 09:06:44AM +0200, Daniel Borkmann wrote:
> > > diff --git a/net/core/filter.c b/net/core/filter.c
> > > index 21d75108c2e9..7aca28b7d0fd 100644
> > > --- a/net/core/filter.c
> > > +++ b/net/core/filter.c
> > > @@ -2492,6 +2492,7 @@ int skb_do_redirect(struct sk_buff *skb)
> > >   			     net_eq(net, dev_net(dev))))
> > >   			goto out_drop;
> > >   		skb->dev = dev;
> > > +		dev_sw_netstats_rx_add(dev, skb->len);
> > 
> > This assumes that all devices that support BPF_F_PEER (currently only
> > veth) use tstats (instead of lstats, or dstats) - is that okay?
> 
> Dumb question, but why all this change and not simply just call ...
> 
>   dev_lstats_add(dev, skb->len)
> 
> ... on the host dev ?

Since I didn't want to update host-veth's TX counters.  If we
bpf_redirect_peer()ed a packet from NIC TC ingress to Pod-veth TC ingress,
I think it means we've bypassed host-veth TX?

> > If not, should I add another NDO e.g. ->ndo_stats_rx_add()?
> 
> Definitely no new stats ndo resp indirect call in fast path.

Yeah, I think I'll put a comment saying that all devices that support
BPF_F_PEER must use tstats (or must use lstats), then.

Thanks,
Peilin Ye