linux-kernel - Re: [PATCH net v2] virtio-net: enable all napis before scheduling refill work

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Message-ID: <CACGkMEtzXmfDhiQiq=5qPGXG+rJcxGkWk0CZ4X_2cnr2UVH+eQ@mail.gmail.com>
Date: Tue, 16 Dec 2025 12:16:43 +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, stable@...r.kernel.org
Subject: Re: [PATCH net v2] virtio-net: enable all napis before scheduling
 refill work

On Fri, Dec 12, 2025 at 11:28 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
> Cc: stable@...r.kernel.org
> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> ---
> Changes in v2:
> - Move try_fill_recv() before rx napi_enable()
> - Link to v1: https://lore.kernel.org/netdev/20251208153419.18196-1-minhquangbui99@gmail.com/
> ---
>  drivers/net/virtio_net.c | 71 +++++++++++++++++++++++++---------------
>  1 file changed, 45 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 8e04adb57f52..4e08880a9467 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3214,21 +3214,31 @@ static void virtnet_update_settings(struct virtnet_info *vi)
>  static int virtnet_open(struct net_device *dev)
>  {
>         struct virtnet_info *vi = netdev_priv(dev);
> +       bool schedule_refill = false;
>         int i, err;
>
> -       enable_delayed_refill(vi);
> -
> +       /* - We must call try_fill_recv before enabling napi of the same receive
> +        * queue so that it doesn't race with the call in virtnet_receive.
> +        * - We must enable and schedule delayed refill work only when we have
> +        * enabled all the receive queue's napi. Otherwise, in refill_work, we
> +        * have a deadlock when calling napi_disable on an already disabled
> +        * napi.
> +        */
>         for (i = 0; i < vi->max_queue_pairs; i++) {
>                 if (i < vi->curr_queue_pairs)
>                         /* Make sure we have some buffers: if oom use wq. */
>                         if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> -                               schedule_delayed_work(&vi->refill, 0);
> +                               schedule_refill = true;
>
>                 err = virtnet_enable_queue_pair(vi, i);
>                 if (err < 0)
>                         goto err_enable_qp;
>         }

So NAPI could be scheduled and it may want to refill but since refill
is not enabled, there would be no refill work.

Is this a problem?


>
> +       enable_delayed_refill(vi);
> +       if (schedule_refill)
> +               schedule_delayed_work(&vi->refill, 0);
> +
>         if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
>                 if (vi->status & VIRTIO_NET_S_LINK_UP)
>                         netif_carrier_on(vi->dev);
> @@ -3463,39 +3473,48 @@ static void virtnet_rx_pause(struct virtnet_info *vi, struct receive_queue *rq)
>         __virtnet_rx_pause(vi, rq);
>  }
>

Thanks