linux-kernel - Re: [PATCH net] virtio-net: enable all napis before scheduling refill work

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Message-ID: <CACGkMEvtKVeoTMrGG0gZOrNKY=m-DGChVcM0TYcqx6-Ap+FY8w@mail.gmail.com>
Date: Tue, 9 Dec 2025 12:30:19 +0800
From: Jason Wang <jasowang@...hat.com>
To: Bui Quang Minh <minhquangbui99@...il.com>
Cc: netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez <eperezma@...hat.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "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>, 
	Stanislav Fomichev <sdf@...ichev.me>, virtualization@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH net] virtio-net: enable all napis before scheduling refill work

On Mon, Dec 8, 2025 at 11:35 PM Bui Quang Minh <minhquangbui99@...il.com> wrote:
>
> Calling napi_disable() on an already disabled napi can cause the
> deadlock. In commit 4bc12818b363 ("virtio-net: disable delayed refill
> when pausing rx"), to avoid the deadlock, when pausing the RX in
> virtnet_rx_pause[_all](), we disable and cancel the delayed refill work.
> However, in the virtnet_rx_resume_all(), we enable the delayed refill
> work too early before enabling all the receive queue napis.
>
> The deadlock can be reproduced by running
> selftests/drivers/net/hw/xsk_reconfig.py with multiqueue virtio-net
> device and inserting a cond_resched() inside the for loop in
> virtnet_rx_resume_all() to increase the success rate. Because the worker
> processing the delayed refilled work runs on the same CPU as
> virtnet_rx_resume_all(), a reschedule is needed to cause the deadlock.
> In real scenario, the contention on netdev_lock can cause the
> reschedule.
>
> This fixes the deadlock by ensuring all receive queue's napis are
> enabled before we enable the delayed refill work in
> virtnet_rx_resume_all() and virtnet_open().
>
> Fixes: 4bc12818b363 ("virtio-net: disable delayed refill when pausing rx")
> Reported-by: Paolo Abeni <pabeni@...hat.com>
> Closes: https://netdev-ctrl.bots.linux.dev/logs/vmksft/drv-hw-dbg/results/400961/3-xdp-py/stderr
> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> ---
>  drivers/net/virtio_net.c | 59 +++++++++++++++++++---------------------
>  1 file changed, 28 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 8e04adb57f52..f2b1ea65767d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2858,6 +2858,20 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
>         return err != -ENOMEM;
>  }
>
> +static void virtnet_rx_refill_all(struct virtnet_info *vi)
> +{
> +       bool schedule_refill = false;
> +       int i;
> +
> +       enable_delayed_refill(vi);

This seems to be still racy?

For example, in virtnet_open() we had:

static int virtnet_open(struct net_device *dev)
{
        struct virtnet_info *vi = netdev_priv(dev);
        int i, err;

        for (i = 0; i < vi->max_queue_pairs; i++) {
                err = virtnet_enable_queue_pair(vi, i);
                if (err < 0)
                        goto err_enable_qp;
        }

        virtnet_rx_refill_all(vi);

So NAPI and refill work is enabled in this case, so the refill work
could be scheduled and run at the same time?

Thanks