Re: [Qemu-devel] Re: [PATCH] vhost-net: Do not set features for backend when peer was deleted

[Michael S. Tsirkin]

On Wed, Oct 27, 2010 at 02:59:16PM +0800, Jason Wang wrote:
> Michael S. Tsirkin writes:
>  > On Wed, Oct 27, 2010 at 12:43:51AM +0800, Jason Wang wrote:
>  > > When hot-unplug a virtio nic with vhost-net backend, guest may
>  > > continue to program the nic even if its peer have been deleted. We can
>  > > not set features at this time as vhost_net_ack_features() may still
>  > > try to use the tap related vhost_net structure which have been freed
>  > > in tap_cleanup(). And setting offload features for a deleted backend
>  > > is also meaningless in this situation
>  > > 
>  > > Signed-off-by: Jason Wang <address@hidden>
>  > 
>  > Hmm. Actually, this is not enough.
>  > We really must stop and cleanup vhost net.
>  > 
> 
> But this patch just prevent the guest from programming a nic with its
> vhost-net backend deleted. The vhost net was still stopped and cleaned
> when the peer have been removed.

No, I think it was cleanup but not stopped first. E.g. try to migrate at
this point and see it crash. I suspect we also leak fds for notifiers
and what not.

>  > Two issues are 
>  > 1. vhost_net_stop needs virtio device pointer
>  > 2. virtio net has a vhost_started flag
>  > 
>  > Two ways to fix it that I see:
>  > 1. add a callback in nic and invoke when peer_deleted is set
>  > 2. add vhost_started and virtio device pointers in vhost
>  > 
>  > Path 1 seems easier ...
>  > 
>  > MST
>  > 
>  > > ---
>  > >  hw/virtio-net.c |    3 +++
>  > >  1 files changed, 3 insertions(+), 0 deletions(-)
>  > > 
>  > > diff --git a/hw/virtio-net.c b/hw/virtio-net.c
>  > > index 7e1688c..68c8e48 100644
>  > > --- a/hw/virtio-net.c
>  > > +++ b/hw/virtio-net.c
>  > > @@ -245,6 +245,9 @@ static void virtio_net_set_features(VirtIODevice 
> *vdev, uint32_t features)
>  > >  {
>  > >      VirtIONet *n = to_virtio_net(vdev);
>  > >  
>  > > +    if (n->nic->peer_deleted)
>  > > +        return;
>  > > +
>  > >      n->mergeable_rx_bufs = !!(features & (1 << VIRTIO_NET_F_MRG_RXBUF));
>  > >  
>  > >      if (n->has_vnet_hdr) {
>  >