Thanks Christian,

I'll confirm that we see error from [2] with that PPA shortly.

In the meantime I've removed the device detach retry logic from OpenStack Nova and now always see two DEVICE_DELETED events raised by QEMU after a single device_del request from libvirt:

http://paste.openstack.org/show/798637/

# zgrep 'debug.*"event": "DEVICE_DELETED"' libvirtd_log.txt.gz 
2020-10-01 21:37:33.180+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588253, "microseconds": 179881}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:37:33.242+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588253, "microseconds": 242565}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 21:40:17.062+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588417, "microseconds": 62704}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:40:17.114+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588417, "microseconds": 113888}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 21:40:20.911+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588420, "microseconds": 911560}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:40:20.985+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588420, "microseconds": 985753}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 21:42:53.528+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588573, "microseconds": 528330}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/net1/virtio-backend"}}]
2020-10-01 21:42:53.583+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588573, "microseconds": 583063}, "event": "DEVICE_DELETED", "data": {"device": "net1", "path": "/machine/peripheral/net1"}}]

2020-10-01 21:44:21.156+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588661, "microseconds": 155903}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/net1/virtio-backend"}}]
2020-10-01 21:44:21.214+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588661, "microseconds": 213714}, "event": "DEVICE_DELETED", "data": {"device": "net1", "path": "/machine/peripheral/net1"}}]

2020-10-01 21:45:55.422+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588755, "microseconds": 422238}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/net1/virtio-backend"}}]
2020-10-01 21:45:55.479+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588755, "microseconds": 479250}, "event": "DEVICE_DELETED", "data": {"device": "net1", "path": "/machine/peripheral/net1"}}]

2020-10-01 21:46:09.001+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588769, "microseconds": 970}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/net1/virtio-backend"}}]
2020-10-01 21:46:09.059+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588769, "microseconds": 58799}, "event": "DEVICE_DELETED", "data": {"device": "net1", "path": "/machine/peripheral/net1"}}]

2020-10-01 21:48:05.182+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588885, "microseconds": 182382}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:48:05.246+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588885, "microseconds": 246077}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 21:48:08.211+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588888, "microseconds": 211386}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/net1/virtio-backend"}}]
2020-10-01 21:48:08.269+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601588888, "microseconds": 269371}, "event": "DEVICE_DELETED", "data": {"device": "net1", "path": "/machine/peripheral/net1"}}]

2020-10-01 21:51:58.384+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589118, "microseconds": 384455}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:51:58.443+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589118, "microseconds": 442848}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 21:52:02.482+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589122, "microseconds": 361461}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk2/virtio-backend"}}]
2020-10-01 21:52:02.482+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589122, "microseconds": 427718}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk2", "path": "/machine/peripheral/virtio-disk2"}}]

2020-10-01 21:52:18.258+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589138, "microseconds": 258652}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:52:18.326+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589138, "microseconds": 325449}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 21:52:43.585+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589163, "microseconds": 585656}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:52:43.656+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589163, "microseconds": 656097}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 21:53:00.216+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589180, "microseconds": 216080}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:53:00.277+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589180, "microseconds": 276944}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 21:53:18.426+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589198, "microseconds": 425877}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:53:18.477+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589198, "microseconds": 477615}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 21:53:35.651+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589215, "microseconds": 252907}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 21:53:35.652+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589215, "microseconds": 304900}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 22:02:58.751+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589778, "microseconds": 751743}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 22:02:58.782+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589778, "microseconds": 782611}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 22:03:02.982+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589782, "microseconds": 982181}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 22:03:03.045+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589783, "microseconds": 45393}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 22:04:05.845+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589845, "microseconds": 845577}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 22:04:05.907+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589845, "microseconds": 907294}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 22:04:08.004+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589848, "microseconds": 4374}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 22:04:08.066+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589848, "microseconds": 66444}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 22:05:52.990+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589952, "microseconds": 990549}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 22:05:53.015+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601589953, "microseconds": 14845}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 22:07:37.477+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601590057, "microseconds": 477326}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 22:07:37.544+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601590057, "microseconds": 544586}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

2020-10-01 22:08:15.655+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601590095, "microseconds": 655117}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/virtio-disk1/virtio-backend"}}]
2020-10-01 22:08:15.717+0000: 55842: debug : qemuMonitorJSONIOProcessLine:220 : Line [{"timestamp": {"seconds": 1601590095, "microseconds": 716847}, "event": "DEVICE_DELETED", "data": {"device": "virtio-disk1", "path": "/machine/peripheral/virtio-disk1"}}]

I'll close this bug out as invalid once I've tested with the PPA and confirmed that we hit the new check.