unmap failed: (16) Device or resource busy

WARNING:root:Packer.pack finished i0e3bf3c0d2944dcc8568f0870b2ec5c1
...
concurrent.futures.process._RemoteTraceback:
"""
Traceback (most recent call last):
  File "/usr/lib/python3.7/concurrent/futures/process.py", line 232, in _process_worker
    r = call_item.fn(*call_item.args, **call_item.kwargs)
  File "bench/bench.py", line 391, in write_and_pack
    packer.pack(image, objects)
  File "bench/bench.py", line 454, in pack
    self.storage_ro.image_remap_ro(image)
  File "bench/bench.py", line 97, in image_remap_ro
    self.image_unmap(image)
  File "bench/bench.py", line 101, in image_unmap
    self.rbd.device.unmap(f"{self.name}/{image}", _ok_code=(0, 22))
  File "/root/bench/.direnv/python-3.7.3/lib/python3.7/site-packages/sh.py", line 1566, in __call__
    return RunningCommand(cmd, call_args, stdin, stdout, stderr)
  File "/root/bench/.direnv/python-3.7.3/lib/python3.7/site-packages/sh.py", line 822, in __init__
    self.wait()
  File "/root/bench/.direnv/python-3.7.3/lib/python3.7/site-packages/sh.py", line 879, in wait
    self.handle_command_exit_code(exit_code)
  File "/root/bench/.direnv/python-3.7.3/lib/python3.7/site-packages/sh.py", line 905, in handle_command_exit_code
    raise exc
sh.ErrorReturnCode_16:

  RAN: /usr/bin/sudo rbd --pool=ro device unmap ro/i0e3bf3c0d2944dcc8568f0870b2ec5c1

  STDOUT:


  STDERR:
rbd: sysfs write failed
rbd: unmap failed: (16) Device or resource busy

"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "bench/bench.py", line 827, in <module>
    sys.exit(asyncio.run(Application().main(sys.argv[1:])))
  File "/usr/lib/python3.7/asyncio/runners.py", line 43, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.7/asyncio/base_events.py", line 584, in run_until_complete
    return future.result()
  File "bench/bench.py", line 820, in main
    await bench.main()
  File "bench/bench.py", line 674, in main
    await rw
  File "bench/bench.py", line 641, in rw_loop
    (image, objects, size) = task.result()
sh.ErrorReturnCode_16:

  RAN: /usr/bin/sudo rbd --pool=ro device unmap ro/i0e3bf3c0d2944dcc8568f0870b2ec5c1

  STDOUT:


  STDERR:
rbd: sysfs write failed
rbd: unmap failed: (16) Device or resource busy