netdev - Re: [PATCH net-next 9/9] net: enetc: add support for XDP

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Message-ID: <20210401113133.vzs3uxkp52k2ctla@skbuf>
Date:   Thu, 1 Apr 2021 14:31:33 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Alexander Duyck <alexander.duyck@...il.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Alex Marginean <alexandru.marginean@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next 9/9] net: enetc: add support for XDP_REDIRECT

On Thu, Apr 01, 2021 at 01:26:02PM +0200, Toke Høiland-Jørgensen wrote:
> > +int enetc_xdp_xmit(struct net_device *ndev, int num_frames,
> > +		   struct xdp_frame **frames, u32 flags)
> > +{
> > +	struct enetc_tx_swbd xdp_redirect_arr[ENETC_MAX_SKB_FRAGS] = {0};
> > +	struct enetc_ndev_priv *priv = netdev_priv(ndev);
> > +	struct enetc_bdr *tx_ring;
> > +	int xdp_tx_bd_cnt, i, k;
> > +	int xdp_tx_frm_cnt = 0;
> > +
> > +	tx_ring = priv->tx_ring[smp_processor_id()];
> 
> What mechanism guarantees that this won't overflow the array? :)

Which array, the array of TX rings?
You mean that it's possible to receive a TC_SETUP_QDISC_MQPRIO or
TC_SETUP_QDISC_TAPRIO with num_tc == 1, and we have 2 CPUs?
Well, yeah, I don't know what's the proper way to deal with that. Ideas?