netdev - Re: virtio_net: suspicious RCU usage with xdp

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Message-ID: <8bcd6aba-ea18-7e20-b883-3b926b9a2c07@redhat.com>
Date:   Fri, 26 Apr 2019 16:00:28 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        David Ahern <dsahern@...il.com>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: virtio_net: suspicious RCU usage with xdp


On 2019/4/26 上午1:41, Jesper Dangaard Brouer wrote:
> It does sound like my commit 5d053f9da431 ("bpf: devmap prepare xdp
> frames for bulking") introduced this issue.  I guess we can add the RCU
> section to xdp_do_flush_map(), and then also verify that the devmap
> (and cpumap) take-down code also have appropriate RCU sections (which
> they should have).
>
> Another requirement for calling .ndo_xdp_xmit is running under NAPI
> protection,


May I know the reason for this? I'm asking since if the packet was 
redirected from tuntap, ndo_xdp_xmit()  won't be called under the 
protection of NAPI (but bh is disabled).

Thanks


> is that still satisifed for veth?
> (even when invoked via xdp_do_flush_map()).