Description of problem:

When cinder-volume uses ceph backend and has debug log and json format log enabled, any backup gets stuck in creating status

~~~
(overcloud) [stack@undercloud-0 ~]$ cinder backup-create b9aeba71-0e10-449a-a755-b1b541002488 --name backup2
+-----------+--------------------------------------+
| Property  | Value                                |
+-----------+--------------------------------------+
| id        | 7419ef7e-f18a-4ab4-95ad-a8632d1647a6 |
| name      | backup2                              |
| volume_id | b9aeba71-0e10-449a-a755-b1b541002488 |
+-----------+--------------------------------------+
(overcloud) [stack@undercloud-0 ~]$ cinder backup-show 7419ef7e-f18a-4ab4-95ad-a8632d1647a6
+-----------------------+--------------------------------------+
| Property              | Value                                |
+-----------------------+--------------------------------------+
| availability_zone     | nova                                 |
| container             | None                                 |
| created_at            | 2020-12-08T01:48:15.000000           |
| data_timestamp        | 2020-12-08T01:48:15.000000           |
| description           | None                                 |
| fail_reason           | None                                 |
| has_dependent_backups | False                                |
| id                    | 7419ef7e-f18a-4ab4-95ad-a8632d1647a6 |
| is_incremental        | False                                |
| name                  | backup2                              |
| object_count          | 0                                    |
| size                  | 1                                    |
| snapshot_id           | None                                 |
| status                | creating                             |
| updated_at            | 2020-12-08T01:48:15.000000           |
| volume_id             | b9aeba71-0e10-449a-a755-b1b541002488 |
+-----------------------+--------------------------------------+
(overcloud) [stack@undercloud-0 ~]$ 
~~~

I don't see any errors in cinder-backup.log or stdout from the cinder-backup container.
I observe the following 2 lines in the bottom of cinder-backup.log
~~~
{"message": "==> connect_volume: call \"{'self': <os_brick.initiator.connectors.rbd.RBDConnector object at 0x7fcd90061550>, 'connection_properties': {'name': 'volumes/volume-b9aeba71-0e10-449a-a755-b1b541002488', 'hosts': ['172.17.3.61', '172.17.3.70', '172.17.3.125'], 'ports': ['6789', '6789', '6789'], 'cluster_name': 'ceph', 'auth_enabled': True, 'auth_username': 'openstack', 'secret_type': 'ceph', 'secret_uuid': '***', 'volume_id': 'b9aeba71-0e10-449a-a755-b1b541002488', 'discard': True, 'keyring': None, 'qos_specs': None, 'access_mode': 'rw', 'encrypted': False}}\"", "asctime": "2020-12-08 01:48:17", "name": "os_brick.initiator.connectors.rbd", "msg": "==> %(func)s: call %(all_args)r", "args": {"func": "connect_volume", "all_args": "{'self': <os_brick.initiator.connectors.rbd.RBDConnector object at 0x7fcd90061550>, 'connection_properties': {'name': 'volumes/volume-b9aeba71-0e10-449a-a755-b1b541002488', 'hosts': ['172.17.3.61', '172.17.3.70', '172.17.3.125'], 'ports': ['6789', '6789', '6789'], 'cluster_name': 'ceph', 'auth_enabled': True, 'auth_username': 'openstack', 'secret_type': 'ceph', 'secret_uuid': '***', 'volume_id': 'b9aeba71-0e10-449a-a755-b1b541002488', 'discard': True, 'keyring': None, 'qos_specs': None, 'access_mode': 'rw', 'encrypted': False}}"}, "levelname": "DEBUG", "levelno": 10, "pathname": "/usr/lib/python3.6/site-packages/os_brick/utils.py", "filename": "utils.py", "module": "utils", "lineno": 146, "funcname": "trace_logging_wrapper", "created": 1607392097.3840482, "msecs": 384.0482234954834, "relative_created": 63425.718784332275, "thread": 140520887643328, "thread_name": "MainThread", "process_name": "MainProcess", "process": 43, "traceback": null, "hostname": "controller-1", "error_summary": "", "context": {"user_name": null, "project_name": "admin", "domain_name": null, "user_domain_name": null, "project_domain_name": null, "user": "b2cfabfa6bc74a9ba0ed91687d280cb3", "tenant": "15b7011587484d6e802741cdbc11dba2", "system_scope": null, "project": "15b7011587484d6e802741cdbc11dba2", "domain": null, "user_domain": "default", "project_domain": "default", "is_admin": true, "read_only": false, "show_deleted": false, "auth_token": "***", "request_id": "req-b525298b-20a6-46c4-863a-94889ccd6034", "global_request_id": "req-681ddf06-8068-4193-8dff-e16b65ed8cd3", "resource_uuid": null, "roles": ["reader", "admin", "member"], "user_identity": "b2cfabfa6bc74a9ba0ed91687d280cb3 15b7011587484d6e802741cdbc11dba2 - default default", "is_admin_project": true, "user_id": "b2cfabfa6bc74a9ba0ed91687d280cb3", "project_id": "15b7011587484d6e802741cdbc11dba2", "domain_id": null, "read_deleted": "no", "remote_address": "172.17.1.20", "timestamp": "2020-12-08T01:48:15.396657+00:00", "quota_class": null, "service_catalog": [{"type": "identity", "name": "keystone", "endpoints": [{"region": "regionOne", "publicURL": "https://10.0.0.101:13000", "adminURL": "http://192.168.24.30:35357", "internalURL": "http://172.17.1.41:5000"}]}, {"type": "image", "name": "glance", "endpoints": [{"region": "regionOne", "adminURL": "http://172.17.1.41:9292", "publicURL": "https://10.0.0.101:13292", "internalURL": "http://172.17.1.41:9292"}]}, {"type": "compute", "name": "nova", "endpoints": [{"region": "regionOne", "adminURL": "http://172.17.1.41:8774/v2.1", "internalURL": "http://172.17.1.41:8774/v2.1", "publicURL": "https://10.0.0.101:13774/v2.1"}]}, {"type": "object-store", "name": "swift", "endpoints": [{"region": "regionOne", "internalURL": "http://172.17.3.41:8080/swift/v1/AUTH_15b7011587484d6e802741cdbc11dba2", "publicURL": "https://10.0.0.101:13808/swift/v1/AUTH_15b7011587484d6e802741cdbc11dba2", "adminURL": "http://172.17.3.41:8080/swift/v1/AUTH_15b7011587484d6e802741cdbc11dba2"}]}]}, "extra": {"project": "15b7011587484d6e802741cdbc11dba2", "version": "unknown"}}
{"message": "opening connection to ceph cluster (timeout=-1).", "asctime": "2020-12-08 01:48:17", "name": "os_brick.initiator.linuxrbd", "msg": "opening connection to ceph cluster (timeout=%s).", "args": [-1], "levelname": "DEBUG", "levelno": 10, "pathname": "/usr/lib/python3.6/site-packages/os_brick/initiator/linuxrbd.py", "filename": "linuxrbd.py", "module": "linuxrbd", "lineno": 70, "funcname": "connect", "created": 1607392097.385284, "msecs": 385.2839469909668, "relative_created": 63426.95450782776, "thread": 140520887643328, "thread_name": "MainThread", "process_name": "MainProcess", "process": 43, "traceback": null, "hostname": "controller-1", "error_summary": "", "context": {"user_name": null, "project_name": "admin", "domain_name": null, "user_domain_name": null, "project_domain_name": null, "user": "b2cfabfa6bc74a9ba0ed91687d280cb3", "tenant": "15b7011587484d6e802741cdbc11dba2", "system_scope": null, "project": "15b7011587484d6e802741cdbc11dba2", "domain": null, "user_domain": "default", "project_domain": "default", "is_admin": true, "read_only": false, "show_deleted": false, "auth_token": "***", "request_id": "req-b525298b-20a6-46c4-863a-94889ccd6034", "global_request_id": "req-681ddf06-8068-4193-8dff-e16b65ed8cd3", "resource_uuid": null, "roles": ["reader", "admin", "member"], "user_identity": "b2cfabfa6bc74a9ba0ed91687d280cb3 15b7011587484d6e802741cdbc11dba2 - default default", "is_admin_project": true, "user_id": "b2cfabfa6bc74a9ba0ed91687d280cb3", "project_id": "15b7011587484d6e802741cdbc11dba2", "domain_id": null, "read_deleted": "no", "remote_address": "172.17.1.20", "timestamp": "2020-12-08T01:48:15.396657+00:00", "quota_class": null, "service_catalog": [{"type": "identity", "name": "keystone", "endpoints": [{"region": "regionOne", "publicURL": "https://10.0.0.101:13000", "adminURL": "http://192.168.24.30:35357", "internalURL": "http://172.17.1.41:5000"}]}, {"type": "image", "name": "glance", "endpoints": [{"region": "regionOne", "adminURL": "http://172.17.1.41:9292", "publicURL": "https://10.0.0.101:13292", "internalURL": "http://172.17.1.41:9292"}]}, {"type": "compute", "name": "nova", "endpoints": [{"region": "regionOne", "adminURL": "http://172.17.1.41:8774/v2.1", "internalURL": "http://172.17.1.41:8774/v2.1", "publicURL": "https://10.0.0.101:13774/v2.1"}]}, {"type": "object-store", "name": "swift", "endpoints": [{"region": "regionOne", "internalURL": "http://172.17.3.41:8080/swift/v1/AUTH_15b7011587484d6e802741cdbc11dba2", "publicURL": "https://10.0.0.101:13808/swift/v1/AUTH_15b7011587484d6e802741cdbc11dba2", "adminURL": "http://172.17.3.41:8080/swift/v1/AUTH_15b7011587484d6e802741cdbc11dba2"}]}]}, "extra": {"project": "15b7011587484d6e802741cdbc11dba2", "version": "unknown"}}
~~~


Version-Release number of selected component (if applicable):
I reproduced the issue with RHOSP16.1.2 .

How reproducible:
Always

Steps to Reproduce:
1. Deploy overcloud with ceph-backup enabled

2. Enable debug and json format log of cinder-backup

/var/lib/config-data/puppet-generated/cinder/etc/cinder/cinder.conf
~~~
[DEFAULT]
...
debug=True
...
use_json = true
~~~

3. Create volume backup
$ cinder backup-create <voume id> --name <backup name>

Actual results:
The created backup gets stuck in creating status

Expected results:
The backup is created and become active

Additional info: