[BUG] perf probe can't insert return kprobe

[Jiri Olsa <jolsa@redhat.com>]

hi,
I couldn't use following perf command to insert return probe:

  # perf probe -a fork_exit=do_fork%return
  Added new event:
  Failed to write event: Invalid argument
    Error: Failed to add events.


I'm pretty sure I used this command before, so seems like
it's broken. I can still use debugfs tracing interface to
do that:
  # echo 'r:do_fork_entry do_fork' > kprobe_events

I used Arnaldo's latest perf/core and FC20 kernel:

  # uname -a
  Linux krava 3.17.7-200.fc20.x86_64 #1 SMP Wed Dec 17 03:35:33 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
  # ./perf version
  perf version 3.18.g6a7d78


thanks,
jirka