Description of problem:
The F7 xen kernel in Dom0 throws the following into the syslog in every 
minute:

BUG: at kernel/irq/manage.c:33 synchronize_irq()

Call Trace:
 <IRQ>  [<ffffffff802aab70>] synchronize_irq+0x52/0x68
 [<ffffffff881855cd>] :3c59x:vortex_timer+0x69/0x380
 [<ffffffff80260038>] _spin_unlock_irq+0x9/0x2f
 [<ffffffff88185564>] :3c59x:vortex_timer+0x0/0x380
 [<ffffffff8028ba2b>] run_timer_softirq+0x138/0x1ac
 [<ffffffff80211a31>] __do_softirq+0x77/0x102
 [<ffffffff8025bd1c>] call_softirq+0x1c/0x300
 [<ffffffff802697ce>] do_softirq+0x56/0xd2
 [<ffffffff80269974>] do_IRQ+0x12a/0x148
 [<ffffffff8038713e>] evtchn_do_upcall+0xac/0x12d
 [<ffffffff8025b7fe>] do_hypervisor_callback+0x1e/0x30
 <EOI>  [<ffffffff802063aa>] hypercall_page+0x3aa/0x1000
 [<ffffffff802063aa>] hypercall_page+0x3aa/0x1000
 [<ffffffff8825d05a>] :ipmi_si:port_inb+0x0/0xf
 [<ffffffff8026ad55>] raw_safe_halt+0xa7/0xcb
 [<ffffffff80268241>] xen_idle+0x49/0x81
 [<ffffffff80247b78>] cpu_idle+0xb7/0xda
 [<ffffffff805a57ca>] start_kernel+0x2aa/0x2af
 [<ffffffff805a511f>] _sinittext+0x11f/0x125


Version-Release number of selected component (if applicable):
2.6.20-2931 and 2936

How reproducible:

Just install F7 xen kernel to a IBM x3400 with an extra 3Com 905 (PCI ID: 
10b7:9200). I suspect from the backtrace that the problem is in the 3com 
driver. Also there's a similar report on the xen mailing list: 
http://lists.xensource.com/archives/html/xen-users/2007-09/msg00620.html

Steps to Reproduce:
1. Use a 3Com905 network card on x86_64 Dom0
2. Watch the syslog messages in every minute
3.
  
Actual results:
Lot of kernel BUG messages

Expected results:
No BUG messages

Additional info:
Previous (before the 2931 version) kernels didn't have this bug. Actually it 
doesn't seem this to cause any other problem, the machine had more than one 
month uptime when I cached this in syslog.