Description: vm connecting to the default virtual net will lose connection after restart the virtual network and restart libvirtd

Version:
libvirt-5.3.0-1.module+el8.1.0+3164+94495c71.x86_64

Reproduce:
100%

Key Words:
Regression, Automation
Not reproduced with libvirt-5.0.0-8.module+el8+3201+fd6ac632.x86_64

PLEASE NOTE, this is quite similar as bz1309529, but we add a step to restart libvirtd. For previous libvirt version, restart libvirtd will make the connection back.


Steps:
1. Having a vm connecting to the default virtual network, and we can PING to it
[root@dell-per740-18 ~]# virsh net-list
 Name      State    Autostart   Persistent
--------------------------------------------
 default   active   yes         yes

[root@dell-per740-18 ~]# virsh net-dumpxml default
<network connections='1'>
  <name>default</name>
  <uuid>6cb5d138-cacd-4dda-84c0-45831d9c1d53</uuid>
  <forward mode='nat'>
    <nat>
      <port start='1024' end='65535'/>
    </nat>
  </forward>
  <bridge name='virbr0' stp='on' delay='0'/>
  <mac address='52:54:00:9d:24:7e'/>
  <ip address='192.168.122.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.122.2' end='192.168.122.254'/>
    </dhcp>
  </ip>
</network>

[root@dell-per740-18 ~]# virsh dumpxml gls | grep "<interface" -A7
    <interface type='network'>
      <mac address='52:54:77:77:77:77'/>
      <source network='default' bridge='virbr0'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>


[root@dell-per740-18 ~]# virsh domif-getlink gls vnet0
vnet0 up

[root@dell-per740-18 ~]# virsh domifaddr gls
 Name       MAC address          Protocol     Address
-------------------------------------------------------------------------------
 vnet0      52:54:77:77:77:77    ipv4         192.168.122.99/24

[root@dell-per740-18 ~]# ping 192.168.122.99 -c 4
PING 192.168.122.99 (192.168.122.99) 56(84) bytes of data.
64 bytes from 192.168.122.99: icmp_seq=1 ttl=64 time=0.290 ms
64 bytes from 192.168.122.99: icmp_seq=2 ttl=64 time=0.272 ms
64 bytes from 192.168.122.99: icmp_seq=3 ttl=64 time=0.269 ms
64 bytes from 192.168.122.99: icmp_seq=4 ttl=64 time=0.270 ms
--- 192.168.122.99 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 78ms


2. Destroy and start the default virtual network, then restart libvirtd, as follow：
[root@dell-per740-18 ~]# virsh net-destroy default; virsh net-start default; service libvirtd restart; sleep 10
Network default destroyed

Network default started

Redirecting to /bin/systemctl restart libvirtd.service


3. Ping the vm again, connection lost
[root@dell-per740-18 ~]# virsh domif-getlink gls vnet0
vnet0 up

[root@dell-per740-18 ~]# virsh domifaddr gls
 Name       MAC address          Protocol     Address
-------------------------------------------------------------------------------
 vnet0      52:54:77:77:77:77    ipv4         192.168.122.99/24

[root@dell-per740-18 ~]# ping 192.168.122.99 -c 4
PING 192.168.122.99 (192.168.122.99) 56(84) bytes of data.
From 192.168.122.1 icmp_seq=1 Destination Host Unreachable
From 192.168.122.1 icmp_seq=2 Destination Host Unreachable
From 192.168.122.1 icmp_seq=3 Destination Host Unreachable
From 192.168.122.1 icmp_seq=4 Destination Host Unreachable
--- 192.168.122.99 ping statistics ---
4 packets transmitted, 0 received, +4 errors, 100% packet loss, time 66ms


Additional info:
Checked another auto job of rhel8.0.0, nothing wrong.
And we cannot manually reproduce this with libvirt-5.0.0-8.module+el8+3201+fd6ac632.x86_64, as follow:
[root@hp-dl320eg8-10 ~]# virsh domifaddr gls
 Name       MAC address          Protocol     Address
-------------------------------------------------------------------------------
 vnet0      52:54:77:77:77:77    ipv4         192.168.122.99/24

[root@hp-dl320eg8-10 ~]# ping -c 4 192.168.122.99
PING 192.168.122.99 (192.168.122.99) 56(84) bytes of data.
64 bytes from 192.168.122.99: icmp_seq=1 ttl=64 time=0.169 ms
64 bytes from 192.168.122.99: icmp_seq=2 ttl=64 time=0.208 ms
64 bytes from 192.168.122.99: icmp_seq=3 ttl=64 time=0.182 ms
64 bytes from 192.168.122.99: icmp_seq=4 ttl=64 time=0.177 ms

--- 192.168.122.99 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 97ms
rtt min/avg/max/mdev = 0.169/0.184/0.208/0.014 ms
[root@hp-dl320eg8-10 ~]# virsh net-destroy default; virsh net-start default; service libvirtd restart
Network default destroyed

Network default started

Redirecting to /bin/systemctl restart libvirtd.service
[root@hp-dl320eg8-10 ~]# ping -c 4 192.168.122.99
PING 192.168.122.99 (192.168.122.99) 56(84) bytes of data.
64 bytes from 192.168.122.99: icmp_seq=1 ttl=64 time=0.288 ms
64 bytes from 192.168.122.99: icmp_seq=2 ttl=64 time=0.155 ms
64 bytes from 192.168.122.99: icmp_seq=3 ttl=64 time=0.182 ms
64 bytes from 192.168.122.99: icmp_seq=4 ttl=64 time=0.163 ms

--- 192.168.122.99 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 58ms
rtt min/avg/max/mdev = 0.155/0.197/0.288/0.053 ms


Expected result:
After destroy/start network and restart libvirtd, the vm should back online.