i386 IPI panic

Hi,
I got a panic on a box which got a SMP kernel yesterday evening (it worked
fine with a  UP kernel for months):
panic: TLP IPI rendezvous failed (mask 1)

Here is the stack trace (although I suspect it's not usefull):
pmap_tlp_shootdown
pmap_do_remove
pmap_remove
ubc_alloc
ffs_write
vn_write
dofilewrite
sys_write

I have similar boxes running SMP without problems, including one with
a similar workload. The only special thing this one has is that it has
some serial port activity (apcupsd running on one of the motherboard ports,
8 serial console connected to a eight ports PUC device, some of them getting
verbose logs).
I've seen in the config file that com needs a special option on i386 SMP,
could it be that the serial driver blocks *all* interrupts (including IPI
ones) for too long ?

-- 
Manuel Bouyer <[email protected]>
     NetBSD: 26 ans d'experience feront toujours la difference
--