linux-kernel - Re: [PATCH net] virtio_net: fix xdp_rxq

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Date:   Tue, 21 Jun 2022 18:55:14 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Stephan Gerhold <stephan.gerhold@...nkonzept.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "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>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>
Cc:     brouer@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH net] virtio_net: fix xdp_rxq_info bug after suspend/resume


On 21/06/2022 13.48, Stephan Gerhold wrote:
> The following sequence currently causes a driver bug warning
> when using virtio_net:
> 
>    # ip link set eth0 up
>    # echo mem > /sys/power/state (or e.g. # rtcwake -s 10 -m mem)
>    <resume>
>    # ip link set eth0 down
> 
>    Missing register, driver bug
>    WARNING: CPU: 0 PID: 375 at net/core/xdp.c:138 xdp_rxq_info_unreg+0x58/0x60

I love seeing that the sanity check we added are actually catching bugs
in drives like this :-)))

>    Call trace:
>     xdp_rxq_info_unreg+0x58/0x60
>     virtnet_close+0x58/0xac
>     __dev_close_many+0xac/0x140
>     __dev_change_flags+0xd8/0x210
>     dev_change_flags+0x24/0x64
>     do_setlink+0x230/0xdd0
>     ...
> 
> This happens because virtnet_freeze() frees the receive_queue
> completely (including struct xdp_rxq_info) but does not call
> xdp_rxq_info_unreg(). Similarly, virtnet_restore() sets up the
> receive_queue again but does not call xdp_rxq_info_reg().
> 
> Actually, parts of virtnet_freeze_down() and virtnet_restore_up()
> are almost identical to virtnet_close() and virtnet_open(): only
> the calls to xdp_rxq_info_(un)reg() are missing. This means that
> we can fix this easily and avoid such problems in the future by
> just calling virtnet_close()/open() from the freeze/restore handlers.
> 
> Aside from adding the missing xdp_rxq_info calls the only difference
> is that the refill work is only cancelled if netif_running(). However,
> this should not make any functional difference since the refill work
> should only be active if the network interface is actually up.
> 
> Fixes: 754b8a21a96d ("virtio_net: setup xdp_rxq_info")
> Signed-off-by: Stephan Gerhold<stephan.gerhold@...nkonzept.com>
> ---
>   drivers/net/virtio_net.c | 25 ++++++-------------------
>   1 file changed, 6 insertions(+), 19 deletions(-)

LGTM

Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>