eBPF command 'mdflush' shows Traceback when exited

Issue

• eBPF command mdflush shows Traceback when exited

[root@host tools]# ./mdflush
Tracing md flush requests... Hit Ctrl-C to end.
TIME     PID    COMM             DEVICE
15:09:47 8115   dd               md0
^CTraceback (most recent call last):
  File "./mdflush", line 81, in <module>
    b.perf_buffer_poll()
  File "/usr/lib/python3.6/site-packages/bcc/__init__.py", line 1216, in perf_buffer_poll
    lib.perf_reader_poll(len(readers), readers, timeout)
KeyboardInterrupt