linux-kernel - Re: [PATCH bpf v2] xdp: fix race on generic receive path

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Date:   Wed, 3 Jul 2019 09:48:09 -0700
From:   William Tu <u9012063@...il.com>
To:     Magnus Karlsson <magnus.karlsson@...il.com>
Cc:     Ilya Maximets <i.maximets@...sung.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Xdp <xdp-newbies@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf v2] xdp: fix race on generic receive path

On Wed, Jul 3, 2019 at 6:20 AM Magnus Karlsson
<magnus.karlsson@...il.com> wrote:
>
> On Wed, Jul 3, 2019 at 2:09 PM Ilya Maximets <i.maximets@...sung.com> wrote:
> >
> > Unlike driver mode, generic xdp receive could be triggered
> > by different threads on different CPU cores at the same time
> > leading to the fill and rx queue breakage. For example, this
> > could happen while sending packets from two processes to the
> > first interface of veth pair while the second part of it is
> > open with AF_XDP socket.
> >
> > Need to take a lock for each generic receive to avoid race.
>
> I measured the performance degradation of rxdrop on my local machine
> and it went from 2.19 to 2.08, so roughly a 5% drop. I think we can
> live with this in XDP_SKB mode. If we at some later point in time need
> to boost performance in this mode, let us look at it then from a
> broader perspective and find the most low hanging fruit.
>
> Thanks Ilya for this fix.
>
> Acked-by: Magnus Karlsson <magnus.karlsson@...el.com>
>
> > Fixes: c497176cb2e4 ("xsk: add Rx receive functions and poll support")
> > Signed-off-by: Ilya Maximets <i.maximets@...sung.com>
> > ---

Tested on my machine and works ok.
Tested-by: William Tu <u9012063@...il.com>