> Could you please provide name and value of the setxattr() call? I bet it's trying to setxattr 'security.selinux' extended file attribute.

(Pdb) bt full
  /usr/lib64/python3.7/pdb.py(1701)main()
-> pdb._runscript(mainpyfile)
  /usr/lib64/python3.7/pdb.py(1570)_runscript()
-> self.run(statement)
  /usr/lib64/python3.7/bdb.py(585)run()
-> exec(cmd, globals, locals)
  <string>(1)<module>()->None
  /tmp/test.py(6)<module>()->None
-> copy2('/tmp/some_file', '/relabel_bug/failure')
  /usr/lib64/python3.7/shutil.py(267)copy2()
-> copystat(src, dst, follow_symlinks=follow_symlinks)
  /usr/lib64/python3.7/shutil.py(209)copystat()
-> _copyxattr(src, dst, follow_symlinks=follow)
> /usr/lib64/python3.7/shutil.py(165)_copyxattr()
-> os.setxattr(dst, name, value, follow_symlinks=follow_symlinks)
(Pdb) p dst
'/relabel_bug/failure'
(Pdb) p name
'security.selinux'
(Pdb) p value
b'system_u:object_r:fusefs_t:s0\x00'
(Pdb)