Comment 18 for bug 1789659

Pre update test:
$ sudo ./test-lp1789659.sh
+ concurrency=40
+ duration=60
+ guests=4
+ uvt-simplestreams-libvirt sync --source http://cloud-images.ubuntu.com/daily arch=amd64 release=bionic label=daily
+ date +%F %T
+ starttime=2018-09-10 10:16:58
+ set +x
+ sleep 60s
uvt-kvm: error: libvirt: storage volume 'b1.qcow' exists already
+ date +%F %T
+ endtime=2018-09-10 10:17:58
+ pkill -P 5261
+ seq 1 4
+ uvt-kvm destroy b1
+ uvt-kvm destroy b2
+ uvt-kvm destroy b3
+ /bin/true
+ uvt-kvm destroy b4
+ /bin/true
+ journalctl -u libvirtd --since 2018-09-10 10:16:58 --until 2018-09-10 10:17:58
+ grep Hash operation
Sep 10 10:16:58 node-horsea libvirtd[3115]: 2018-09-10 10:16:58.914+0000: 3277: error : virHashForEach:597 : Hash operation not allowed during iteration
Sep 10 10:16:59 node-horsea libvirtd[3115]: 2018-09-10 10:16:59.326+0000: 3278: error : virHashForEach:597 : Hash operation not allowed during iteration
[...] ~80 of them

Update:
$ sudo apt install libvirt-clients libvirt-daemon libvirt-daemon-driver-storage-rbd libvirt-daemon-system libvirt0
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  linux-headers-4.15.0-32 linux-headers-4.15.0-32-generic linux-image-4.15.0-32-generic linux-modules-4.15.0-32-generic linux-modules-extra-4.15.0-32-generic
Use 'sudo apt autoremove' to remove them.
Suggested packages:
  libvirt-daemon-driver-storage-gluster libvirt-daemon-driver-storage-sheepdog libvirt-daemon-driver-storage-zfs numad radvd auditd systemtap nfs-common zfsutils pm-utils
The following packages will be upgraded:
  libvirt-clients libvirt-daemon libvirt-daemon-driver-storage-rbd libvirt-daemon-system libvirt0
5 upgraded, 0 newly installed, 0 to remove and 7 not upgraded.
Need to get 4.115 kB of archives.
After this operation, 4.096 B disk space will be freed.
Get:1 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libvirt-daemon-system amd64 4.0.0-1ubuntu8.5 [80,7 kB]
Get:2 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libvirt-clients amd64 4.0.0-1ubuntu8.5 [595 kB]
Get:3 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libvirt-daemon-driver-storage-rbd amd64 4.0.0-1ubuntu8.5 [15,4 kB]
Get:4 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libvirt-daemon amd64 4.0.0-1ubuntu8.5 [2.173 kB]
Get:5 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libvirt0 amd64 4.0.0-1ubuntu8.5 [1.251 kB]
Fetched 4.115 kB in 1s (4.609 kB/s)
Preconfiguring packages ...
(Reading database ... 197154 files and directories currently installed.)
Preparing to unpack .../libvirt-daemon-system_4.0.0-1ubuntu8.5_amd64.deb ...
Unpacking libvirt-daemon-system (4.0.0-1ubuntu8.5) over (4.0.0-1ubuntu8.4) ...
Preparing to unpack .../libvirt-clients_4.0.0-1ubuntu8.5_amd64.deb ...
Unpacking libvirt-clients (4.0.0-1ubuntu8.5) over (4.0.0-1ubuntu8.4) ...
Preparing to unpack .../libvirt-daemon-driver-storage-rbd_4.0.0-1ubuntu8.5_amd64.deb ...
Unpacking libvirt-daemon-driver-storage-rbd (4.0.0-1ubuntu8.5) over (4.0.0-1ubuntu8.4) ...
Preparing to unpack .../libvirt-daemon_4.0.0-1ubuntu8.5_amd64.deb ...
Unpacking libvirt-daemon (4.0.0-1ubuntu8.5) over (4.0.0-1ubuntu8.4) ...
Preparing to unpack .../libvirt0_4.0.0-1ubuntu8.5_amd64.deb ...
Unpacking libvirt0:amd64 (4.0.0-1ubuntu8.5) over (4.0.0-1ubuntu8.4) ...
Processing triggers for ureadahead (0.100.0-20) ...
Setting up libvirt0:amd64 (4.0.0-1ubuntu8.5) ...
Setting up libvirt-daemon (4.0.0-1ubuntu8.5) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Processing triggers for systemd (237-3ubuntu10.3) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Setting up libvirt-clients (4.0.0-1ubuntu8.5) ...
Setting up libvirt-daemon-system (4.0.0-1ubuntu8.5) ...
Installing new version of config file /etc/apparmor.d/usr.sbin.libvirtd ...
virtlockd.service is a disabled or a static unit, not starting it.
Setting up libvirt-daemon dnsmasq configuration.
Setting up libvirt-daemon-driver-storage-rbd (4.0.0-1ubuntu8.5) ...

Post Update test:
$ sudo ./test-lp1789659.sh
+ concurrency=40
+ duration=60
+ guests=4
+ uvt-simplestreams-libvirt sync --source http://cloud-images.ubuntu.com/daily arch=amd64 release=bionic label=daily
+ date +%F %T
+ starttime=2018-09-10 10:19:52
+ set +x
+ sleep 60s
+ date +%F %T
+ endtime=2018-09-10 10:20:52
+ pkill -P 4122
+ seq 1 4
+ uvt-kvm destroy b1
+ uvt-kvm destroy b2
+ uvt-kvm destroy b3
+ uvt-kvm destroy b4
+ /bin/true
+ journalctl -u libvirtd --since 2018-09-10 10:19:52 --until 2018-09-10 10:20:52
+ grep Hash operation
+ /bin/true

=> No trigger of the issue anymore.
Setting verification done