Re: [question]vhost-user: atuo fix network link broken during migration

[Jason Wang]

On 2020/3/23 下午4:17, yangke (J) wrote:
> We find an issue when host mce trigger openvswitch(dpdk) restart in source host 
> during guest migration,


Did you mean the vhost-user netev was deleted from the source host?


> VM is still link down in frontend after migration, it cause the network in VM 
> never be up again.
>
> virtio_net_load_device:
>      /* nc.link_down can't be migrated, so infer link_down according
>       * to link status bit in n->status */
>      link_down = (n->status & VIRTIO_NET_S_LINK_UP) == 0;
>      for (i = 0; i < n->max_queues; i++) {
>          qemu_get_subqueue(n->nic, i)->link_down = link_down;
>      }
>
> guset:                    migrate begin -------> vCPU pause --------> vmsate load 
> ------->migrate finish
>                                              ^                  ^               
>       ^
>                                              |                  |               
>       |
> openvswitch in source host:          begin to restart       restarting          
>    started
>                                              ^                  ^               
>       ^
>                                              |                  |               
>       |
> nc in frontend in source:               link down           link down           
>   link down
>                                              ^                  ^               
>       ^
>                                              |                  |               
>       |
> nc in frontend in destination:          link up             link up             
>   link down
>                                              ^                  ^               
>       ^
>                                              |                  |               
>       |
> guset network:                            broken             broken             
>    broken
>                                              ^                  ^               
>       ^
>                                              |                  |               
>       |
> nc in backend in source:                link down          link down            
>   link up
>                                              ^                  ^               
>       ^
>                                              |                  |               
>       |
> nc in backend in destination:           link up             link up             
>   link up
>
> The link_down of frontend was loaded from n->status, n->status is link down in 
> source, so the link_down of
> frontend is true. The backend in destination host is link up, but the frontend 
> in destination host is
> link down, it cause the network in gust never be up again until an guest cold 
> reboot.
>
> Is there a way to auto fix the link status? or just abort the migration in 
> virtio net device load?


Maybe we can try to sync link status after migration?

Thanks