Verified with versions:
# rpm -q libvirt
libvirt-0.9.10-21.el6_3.2.x86_64
Following the steps in bug 822373 Description.
300 times loop attach/detach all successfully.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
http://rhn.redhat.com/errata/RHBA-2012-1095.html