linux-kernel - Re: [RFC 1/2] virtio_net: timeout control virtqueue commands

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Message-ID: <CAJaqyWeuMvkj2HzCrph+h-rjYdTMQJRcAvHzryKt6iUhd4sEsQ@mail.gmail.com>
Date: Tue, 14 Oct 2025 09:30:04 +0200
From: Eugenio Perez Martin <eperezma@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: mst@...hat.com, Yongji Xie <xieyongji@...edance.com>, virtualization@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Maxime Coquelin <mcoqueli@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Dragos Tatulea DE <dtatulea@...dia.com>
Subject: Re: [RFC 1/2] virtio_net: timeout control virtqueue commands

On Sat, Oct 11, 2025 at 9:45 AM Jason Wang <jasowang@...hat.com> wrote:
>
> On Tue, Oct 7, 2025 at 9:06 PM Eugenio Pérez <eperezma@...hat.com> wrote:
> >
> > An userland device implemented through VDUSE could take rtnl forever if
> > the virtio-net driver is running on top of virtio_vdpa.  Let's break the
> > device if it does not return the buffer in a longer-than-assumible
> > timeout.
> >
> > A less agressive path can be taken to recover the device, like only
> > resetting the control virtqueue.  However, the state of the device after
> > this action is taken races, as the vq could be reset after the device
> > writes the OK.  Leaving TODO anyway.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> > ---
> >  drivers/net/virtio_net.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 31bd32bdecaf..ed68ad69a019 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -3576,6 +3576,7 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
> >  {
> >         struct scatterlist *sgs[5], hdr, stat;
> >         u32 out_num = 0, tmp, in_num = 0;
> > +       unsigned long end_time;
> >         bool ok;
> >         int ret;
> >
> > @@ -3614,11 +3615,20 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
> >
> >         /* Spin for a response, the kick causes an ioport write, trapping
> >          * into the hypervisor, so the request should be handled immediately.
> > +        *
> > +        * Long timeout so a malicious device is not able to lock rtnl forever.
> >          */
> > +       end_time = jiffies + 30 * HZ;
>
> The problem that 30 * HZ is probably long enough to trigger the
> warnings like hungtask?
>

That's right. OTOH, the same behavior from the device already triggers
the hungtask.

Maybe it is better to set it to 15*HZ?