Comment 12 for bug 1882521

Ignore the less interesting comment#11, the more "interesting" bit from the libvirtd.log is here:

libvirt asks QEMU to execute 'device_del' (i.e. to detach the device from the guest):

---
2020-09-03 19:58:35.441+0000: 65331: info : qemuMonitorSend:993 : QEMU_MONITOR_SEND_MSG: mon=0x7f021c0b9c70 msg={"execute":"device_del","arguments":{"id":"virtio-disk1"},"id":"libvirt-399"}
 fd=-1
---

But the reply from QEMU is failure to detach the device:

---
2020-09-03 19:58:35.443+0000: 65328: info : qemuMonitorJSONIOProcessLine:239 : QEMU_MONITOR_RECV_REPLY: mon=0x7f021c0b9c70 reply={"id": "libvirt-399", "error": {"class": "DeviceNotFound", "d
esc": "Device 'virtio-disk1' not found"}}

[...]

93e20 name=instance-0000007a)
2020-09-03 19:58:35.443+0000: 65331: debug : qemuDomainDeleteDevice:128 : Detaching of device virtio-disk1 failed and no event arrived
---

I learn the above "... no event arrived" means QEMU didn't tell libvirt which device was deleted.

I still don't have a robust answer to the root cause yet.