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Message-ID: <1714448630.5571823-1-xuanzhuo@linux.alibaba.com>
Subject: Re: [PATCH v3 1/2] vhost: destroy device when all vqs are inactive
Date: Tue, 30 Apr 2024 11:43:50 +0800
From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Kangjie Xu <kangjie.xu@linux.alibaba.com>, chenbo.xia@intel.com,
dev@dpdk.org, hengqi@linux.alibaba.com, jasowang@redhat.com,
mst@redhat.com, Maxime Coquelin <maxime.coquelin@redhat.com>
References: <cover.1662952732.git.kangjie.xu@linux.alibaba.com>
<0383bb821dd65d8511a91e9f13b193230be59557.1662952732.git.kangjie.xu@linux.alibaba.com>
<72b778f6-c813-4b20-1b9c-834d22191a5b@redhat.com>
<20240429092742.3e717890@hermes.local>
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On Mon, 29 Apr 2024 09:27:42 -0700, Stephen Hemminger <stephen@networkplumber.org> wrote:
> On Tue, 11 Oct 2022 18:44:28 +0200
> Maxime Coquelin <maxime.coquelin@redhat.com> wrote:
>
> > On 9/12/22 05:36, Kangjie Xu wrote:
> > > We change the behavior of vhost_user_get_vring_base(). Previosly,
> > > destroying a virtqueue will cause the whole device to be destroyed.
> > > The behavior is not specified in the vhost-user protocol.
> > >
> > > Thus, we refactor this part. The device will be destroyed only when
> > > all virtqueues in the device are going to be destroyed.
> > >
> > > This helps us to simplify the implementation when resetting a virtqueue.
> > >
> > > Signed-off-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > ---
> > > lib/vhost/vhost_user.c | 10 ++++++++--
> > > 1 file changed, 8 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> > > index 4ad28bac45..a9f0709f94 100644
> > > --- a/lib/vhost/vhost_user.c
> > > +++ b/lib/vhost/vhost_user.c
> > > @@ -2088,10 +2088,16 @@ vhost_user_get_vring_base(struct virtio_net **pdev,
> > > {
> > > struct virtio_net *dev = *pdev;
> > > struct vhost_virtqueue *vq = dev->virtqueue[ctx->msg.payload.state.index];
> > > + uint32_t i, num_live_vring = 0;
> > > uint64_t val;
> > >
> > > - /* We have to stop the queue (virtio) if it is running. */
> > > - vhost_destroy_device_notify(dev);
> > > + /* Stop the device when vq is the last active queue */
> > > + for (i = 0; i < dev->nr_vring; i++)
> > > + if (dev->virtqueue[i]->access_ok)
> > > + num_live_vring++;
> > > +
> > > + if (num_live_vring == 1 && vq->access_ok)
> > > + vhost_destroy_device_notify(dev);
> > >
> > > dev->flags &= ~VIRTIO_DEV_READY;
> > > dev->flags &= ~VIRTIO_DEV_VDPA_CONFIGURED;
> >
> > I think we are missing something here.
> >
> > We used to send the device destroy notification before getting the ring
> > indexes, in order to ensure that the application has stopped processing
> > the rings.
> >
> > With this patch, the application may still be polling the ring while we
> > get the ring indexes (e.g. a thread in the application may be in the
> > middle of rte_vhost_dequeue_burst() on that ring). So at best the ring
> > indexes returned to the Vhost-user master will be outdated. At worst, it
> > will crash the application because we call vring_invalidate() without
> > the vq's lock being taken.
> >
> > I think you should protect all the VQ indexes fetching and VQ deinit
> > using its access_lock.
> >
> > Maxime
> >
>
> Please address Maxime's feedback.
Kangjie has already resigned.
Sorry, we don't have anyone in charge of this.
If you need it, you can propose a new patch to solve this problem.
Thanks.