I verify this bug by the following steps:
(1) Create a PV domain
(2) Reboot it
(3) Repeat 2.
After I reboot the guest for 11 times, and find no more any crash. Seems the problem is not exist now. So this bug is verified with the xen-3.0.3-94.el5_4.1
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.
http://rhn.redhat.com/errata/RHSA-2009-1472.html