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Message-ID: <CACGkMEs+Mse7nhPPiqbd2doeGtPD2QD3BM_cztr6e=VfuiobHQ@mail.gmail.com>
Date: Wed, 17 Dec 2025 10:58:27 +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 Wed, Dec 17, 2025 at 12:23 AM Bui Quang Minh
<minhquangbui99@...il.com> wrote:
>
> On 12/16/25 11:16, Jason Wang wrote:
> > 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?
>
> You are right. It is indeed a problem.
>
> I think we can unconditionally schedule the delayed refill after
> enabling all the RX NAPIs (don't check the boolean schedule_refill
> anymore) to ensure that we will have refill work. We can still keep the
> try_fill_recv here to fill the receive buffer earlier in normal case.
> What do you think?
Or we can have a reill_pending but basically I think we need something
that is much more simple. That is, using a per rq work instead of a
global one?
Thanks
>
> >
> >
> >> + 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
> >
>
> Thanks,
> Quang Minh.
>
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