Ocassional OSError: [Errno 16] Device or resource busy when deleting CPU set

[MabezDev]

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My shutdown qemu hook:

# undo the isolation
vfio-isolate cpuset-delete /host.slice
vfio-isolate cpuset-delete /emu.slice
vfio-isolate cpuset-delete /machine.slice

# undo
vfio-isolate restore /tmp/undo_irq
vfio-isolate restore /tmp/undo_gov

Full stack trace:

Traceback (most recent call last):
  File "/home/mabez/programs/vfio-isolate/bin/vfio-isolate", line 33, in <module>
    sys.exit(load_entry_point('vfio-isolate==0.3.1', 'console_scripts', 'vfio-isolate')())
  File "/home/mabez/programs/vfio-isolate/lib/python3.9/site-packages/vfio_isolate/cli.py", line 182, in run_cli
    executor.run()
  File "/home/mabez/programs/vfio-isolate/lib/python3.9/site-packages/vfio_isolate/cli.py", line 175, in run
    e.action.execute(e.params)
  File "/home/mabez/programs/vfio-isolate/lib/python3.9/site-packages/vfio_isolate/action/cpuset_delete.py", line 16, in execute
    cpu_set.remove()
  File "/home/mabez/programs/vfio-isolate/lib/python3.9/site-packages/vfio_isolate/cpuset.py", line 54, in remove
    os.rmdir(self.__path())
OSError: [Errno 16] Device or resource busy: '/sys/fs/cgroup/cpuset/host.slice'

This happens very rarely, but enough to annoy me into reporting it :D