This bugzilla has Keywords: Regression.  

Since no regressions are allowed between releases, 
it is also being proposed as a blocker for this release.  

Please resolve ASAP.

Created attachment 324805 [details]
Posted patch to rhel4.8

Committed in 78.22.EL . RPMS are available at http://people.redhat.com/vgoyal/rhel4/

I have verified this bug on dell-pe2900-02.rhts.bos.redhat.com.
First, with 2.6.9-78.ElxenU and "vif= [ 'type=ioemu' ]", the RHEL4-U7
guest will crash:
...
                Welcome to Red Hat Enterprise Linux AS
                Press 'I' to enter interactive startup.
Cannot access the Hardware Clock via any known method.
Use the --debug option to see the details of our search for an access method.
Setting clock  (localtime): Wed Apr 22 07:22:27 EDT 2009 [  OK  ]
Starting udev:  [  OK  ]
Initializing hardware...  storage----------- [cut here ] --------- [please bite here ] ---------
Kernel BUG at dev:3006
invalid operand: 0000 [1] SMP 
CPU 0 
Modules linked in: xennet dm_snapshot dm_zero dm_mirror ext3 jbd dm_mod xenblk sd_mod scsi_mod
Pid: 7, comm: xenwatch Not tainted 2.6.9-78.ELxenU
RIP: e030:[<ffffffff80242d63>] <ffffffff80242d63>{free_netdev+30}
RSP: e02b:ffffff8000ab7e20  EFLAGS: 00010293
RAX: 0000000000000002 RBX: 00000000fffffffe RCX: 0000000100ab6000
RDX: ffffff8000ab6000 RSI: 0000000000000000 RDI: ffffff801e980000
RBP: fffffffffffffffe R08: ffffff8000ab6000 R09: 0000000300000000
R10: 0000000300000000 R11: 0000000000000002 R12: ffffff801e980380
R13: ffffff801e981d30 R14: ffffff80019e9e00 R15: ffffffff80146108
FS:  0000002a95573b00(0000) GS:ffffffff80428200(0000) knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000
Process xenwatch (pid: 7, threadinfo ffffff8000ab6000, task ffffff8000a837f0)
Stack: ffffffffa009a44c ffffff801f19add7 ffffff801e980000 ffffff801e980380 
       ffffff80019e9e00 00000000fffffffc ffffff8000011da8 0000000100000001 
       ffffff801f187500 ffffffff80358060 
Call Trace:<ffffffffa009a44c>{:xennet:backend_changed+2215} <ffffffff80146108>{keventd_create_kthread+0} 
       <ffffffff8022797d>{xenwatch_handle_callback+21} <ffffffff80227b2d>{xenwatch_thread+381} 
       <ffffffff8012ea2c>{autoremove_wake_function+0} <ffffffff8012ea2c>{autoremove_wake_function+0} 
       <ffffffff802279b0>{xenwatch_thread+0} <ffffffff801460df>{kthread+200} 
       <ffffffff8010e196>{child_rip+8} <ffffffff80146108>{keventd_create_kthread+0} 
       <ffffffff80146017>{kthread+0} <ffffffff8010e18e>{child_rip+0} 
       

Code: 0f 0b 7e d4 2a 80 ff ff ff ff be 0b c7 87 10 02 00 00 05 00 
RIP <ffffffff80242d63>{free_netdev+30} RSP <ffffff8000ab7e20>
 <0>Kernel panic - not syncing: Oops

And with 2.6.9-88.ELxenU, the guest works fine.
Will change the status to "VERIFIED". Thanks!

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-2009-1024.html