autovacuum locks

Folks,

I got a system here (8.3.7), that is locked up. Few queries waiting
for autovacuum aquired locks on a table or two.
But it looks like autovacuum is also waiting for some semaphore:

#0 0x00f07410 in __kernel_vsyscall ()
#1 0x00252d2b in semop () from /lib/libc.so.6
#2 0x081ca1ce in PGSemaphoreLock ()
#3 0x081f590e in ProcWaitForSignal ()
#4 0x081e8dea in LockBufferForCleanup ()
#5 0x08160e68 in ?? ()
#6 0x08161482 in lazy_vacuum_rel ()
#7 0x081603b5 in ?? ()
#8 0x081605c4 in vacuum ()
#9 0x081cd154 in ?? ()
#10 0x081cd7f1 in ?? ()
#11 0x081cd911 in StartAutoVacWorker ()
#12 0x081d6d47 in ?? ()
#13 <signal handler called>
#14 0x00f07410 in __kernel_vsyscall ()
#15 0x00249fcd in ___newselect_nocancel () from /lib/libc.so.6
#16 0x081d3964 in ?? ()
#17 0x081d5105 in PostmasterMain ()
#18 0x0818be60 in main ()

There's still other transcations going on , and working fine - but two
tables seem to be cut out by autovacuum, and other queries stuck
waiting for autovacuum to finish.

Any ideas ?
Is there a possible fix up the 8.3 stream, that would target that ? (I
need leverage to upgrade to 8.3.18, and if that's the case - happy
days).

--
GJ