Hung postmaster (8.3.9)

Need some help.

My PostgreSQL 8.3.6 and now 8.3.9 postmaster is hanging.
No idea why, been running like a top for a year.
Can't do "select version()", even hung after system reboot.
SIGINT/QUIT/TERM have no effect, only SIGKILL can stop it.

This is Linux 2.6.18-92.1.22.el5 SMP x86_64

Here's the log after restarting from SIGKILL:

2010-02-27 20:11:10.426 CST [23134] LOG: database system was interrupted; last known up at 2010-02-27 20:08:46 CST
2010-02-27 20:11:10.426 CST [23134] DEBUG: checkpoint record is at 8BC/63F5FC0
2010-02-27 20:11:10.426 CST [23134] DEBUG: redo record is at 8BC/63F5FC0; shutdown TRUE
2010-02-27 20:11:10.426 CST [23134] DEBUG: next transaction ID: 0/488483782; next OID: 1619873999
2010-02-27 20:11:10.426 CST [23134] DEBUG: next MultiXactId: 130401682; next MultiXactOffset: 830996786
2010-02-27 20:11:10.426 CST [23134] LOG: database system was not properly shut down; automatic recovery in progress
2010-02-27 20:11:10.497 CST [23134] LOG: record with zero length at 8BC/63F6020
2010-02-27 20:11:10.497 CST [23134] LOG: redo is not required
2010-02-27 20:11:10.503 CST [23134] LOG: checkpoint starting: shutdown immediate
2010-02-27 20:11:10.581 CST [23134] LOG: checkpoint complete: wrote 0 buffers (0.0%); 0 transaction log file(s) added, 0 removed, 0 recycled; write=0.045 s, sync=0.000 s, total=0.083 s
2010-02-27 20:11:10.587 CST [23134] DEBUG: transaction ID wrap limit is 2435542396, limited by database "ohsdba"
2010-02-27 20:11:10.589 CST [23134] DEBUG: proc_exit(0)
2010-02-27 20:11:10.589 CST [23134] DEBUG: shmem_exit(0)
2010-02-27 20:11:10.592 CST [23134] DEBUG: exit(0)

Here's the backtrace:

$ gdb `which postgres`
GNU gdb Fedora (6.8-37.el5)
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu"...
(gdb) attach 3776
Attaching to program: /opt/pgsql/installs/postgresql-8.3.9/bin/postgres, process 3776
Reading symbols from /lib64/libcrypt.so.1...done.
Loaded symbols for /lib64/libcrypt.so.1
Reading symbols from /lib64/libdl.so.2...done.
Loaded symbols for /lib64/libdl.so.2
Reading symbols from /lib64/libm.so.6...done.
Loaded symbols for /lib64/libm.so.6
Reading symbols from /lib64/libc.so.6...done.
Loaded symbols for /lib64/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Reading symbols from /lib64/libnss_files.so.2...done.
Loaded symbols for /lib64/libnss_files.so.2
0x000000346f8c43a0 in __read_nocancel () from /lib64/libc.so.6
(gdb) p debug_query_string
$1 = 0x0
(gdb) bt
#0 0x000000346f8c43a0 in __read_nocancel () from /lib64/libc.so.6
#1 0x000000346f86c747 in _IO_new_file_underflow () from /lib64/libc.so.6
#2 0x000000346f86d10e in _IO_default_uflow_internal () from /lib64/libc.so.6
#3 0x000000346f8689cb in getc () from /lib64/libc.so.6
#4 0x0000000000531ee8 in next_token (fp=0x5b90f20, buf=0x7fff59bef330 "", bufsz=4096) at hba.c:128
#5 0x0000000000532233 in tokenize_file (filename=0x5b8f3f0 "global", file=0x5b90f20, lines=0x7fff59bef5c8,
line_nums=0x7fff59bef5c0) at hba.c:232
#6 0x00000000005322e9 in tokenize_file (filename=0x5b8f3d0 "global/pg_auth", file=0x5b90ce0, lines=0x98b168, line_nums=0x98b170)
at hba.c:358
#7 0x00000000005327ff in load_role () at hba.c:959
#8 0x000000000057f300 in reaper (postgres_signal_arg=<value optimized out>) at postmaster.c:2145
#9 <signal handler called>
#10 0x000000346f8cb323 in __select_nocancel () from /lib64/libc.so.6
#11 0x000000000057cc33 in ServerLoop () at postmaster.c:1236
#12 0x000000000057dfdf in PostmasterMain (argc=6, argv=0x5b73fe0) at postmaster.c:1031
#13 0x00000000005373de in main (argc=6, argv=<value optimized out>) at main.c:188
(gdb) quit
The program is running. Quit anyway (and detach it)? (y or n) y
Detaching from program: /opt/pgsql/installs/postgresql-8.3.9/bin/postgres, process 3776

Thanks in advance for any help.

Ed