gdb unable to read python frame information

[Wesley]

Hi guys,
  My env: centos 6.5 64 bit; gdb 7.1; python 2.6.6

I wanna use gdb to attach my running python scripts.
Successfully import libpython in gdb, but seems all py operations failed to read python information.

Here is the snippet:
(gdb) python
>import libpython
>end
(gdb) py-bt
#3 (unable to read python frame information)
#5 (unable to read python frame information)
#7 (unable to read python frame information)
#9 (unable to read python frame information)
#18 (unable to read python frame information)
#22 (unable to read python frame information)
#26 (unable to read python frame information)
#28 (unable to read python frame information)
#29 (unable to read python frame information)
#38 (unable to read python frame information)
#39 (unable to read python frame information)
#40 (unable to read python frame information)
#42 (unable to read python frame information)
#44 (unable to read python frame information)
#45 (unable to read python frame information)
#47 (unable to read python frame information)
#49 (unable to read python frame information)
#51 (unable to read python frame information)
#55 (unable to read python frame information)
#62 (unable to read python frame information)
#64 (unable to read python frame information)
#76 (unable to read python frame information)
#88 (unable to read python frame information)
#100 (unable to read python frame information)
(gdb) py-locals
Unable to read information on python frame
(gdb) 

Is there anything wrong?
Thanks.
Wesley