RELENG_6 frequent crashes

[Vlad GALU]

     Unfortunately this is the third time I report this. This panic
occurs every 2 to 6 days. So far I've never managed to go over a
week's uptime. Between crashes I've periodically updated to the latest
RELENG_6. Here's the full backtrace:

-- cut here --
(kgdb) bt fu
#0  doadump () at pcpu.h:165
No locals.
#1  0xc0582b84 in boot (howto=260) at ../../../kern/kern_shutdown.c:409
        first_buf_printf = 1
#2  0xc0583117 in panic (
    fmt=0xc0751ab1 "vm_page_unwire: invalid wire count: %d")
    at ../../../kern/kern_shutdown.c:565
        bootopt = 260
        newpanic = 0
        buf = "vm_page_unwire: invalid wire count: 0", '\0' <repeats 218 times>
#3  0xc06c4c00 in vm_page_unwire (m=0xc2669220, activate=0)
    at ../../../vm/vm_page.c:1197
No locals.
#4  0xc05d4d75 in vfs_vmio_release (bp=0xda610da8)
    at ../../../kern/vfs_bio.c:1470
        i = 3
        m = 0xc2669220
#5  0xc05d8509 in getnewbuf (slpflag=0, slptimeo=0, size=16384, maxsize=16384)
    at ../../../kern/vfs_bio.c:1779
        addr = 3663760120
        bp = (struct buf *) 0xda610da8
        nbp = (struct buf *) 0xda497348
        defrag = 0
        nqindex = 1
        flushingbufs = 0
#6  0xc05d890e in getblk (vp=0xca945220, blkno=9273, size=16384, slpflag=0,
    slptimeo=0, flags=0) at ../../../kern/vfs_bio.c:2486
        bsize = 16384
        maxsize = 0
        vmio = 1
        offset = 151928832
        bp = (struct buf *) 0x4000
        bo = (struct bufobj *) 0xca9452e0
#7  0xc067faf6 in ffs_balloc_ufs2 (vp=0xca945220,
startoffset=Unhandled dwarf expression opcode 0x93
)
    at ../../../ufs/ffs/ffs_balloc.c:817
        ip = (struct inode *) 0xca8eb8c4
        dp = (struct ufs2_dinode *) 0xca21fd00
        lbn = 9273
        lastlbn = 11187
        fs = (struct fs *) 0xc8622000
        bp = (struct buf *) 0xda608af8
        nbp = (struct buf *) 0xc05dea5f
        ump = (struct ufsmount *) 0xc8396a00
        indirs = {{in_lbn = -2061, in_off = 1, in_exists = 0}, {
    in_lbn = -2061, in_off = 3, in_exists = 0}, {in_lbn = -8204,
    in_off = 1069, in_exists = 0}, {in_lbn = 8589934591, in_off = 0,
    in_exists = 0}, {in_lbn = -1828101238395240448, in_off = -1067988038,
    in_exists = -969433728}}
        nb = Unhandled dwarf expression opcode 0x93
(kgdb)
-- and here --

My kernel looks like this:
-- cut here --
machine         i386
cpu             I686_CPU
ident           ANONYMOUS
maxusers        0
options         HZ=100
options         INCLUDE_CONFIG_FILE
makeoptions     DEBUG=-g
options         SCHED_4BSD
options         COMPAT_FREEBSD5
options         KTRACE
options         _KPOSIX_PRIORITY_SCHEDULING
options         PREEMPTION
options         ADAPTIVE_GIANT
options         DDB
options         KDB
options         KDB_UNATTENDED
options         BLKDEV_IOSIZE=8192
options         DFLDSIZ="(128UL*1024*1024)"
options         MAXDSIZ="(1024UL*1024*1024)"
options         MAXSSIZ="(384UL*1024*1024)"
options         SYSVSHM
options         SHMMAXPGS=4096
options         SHMMAX="(SHMMAXPGS*PAGE_SIZE)+1"
options         SHMALL="(SHMMAXPGS*PAGE_SIZE)+1"
options         SYSVMSG
options         SYSVSEM
options         HWPMC_HOOKS
options         INET
options         INET6
options         IPSTEALTH
options         TCP_DROP_SYNFIN
options         ZERO_COPY_SOCKETS
options         ACCEPT_FILTER_DATA
options         ACCEPT_FILTER_HTTP
options         FFS
options         SOFTUPDATES
options         UFS_DIRHASH
options         CD9660
options         PSEUDOFS
options         PROCFS
options         FDESCFS
options         NULLFS
options         MD_ROOT
options         MAC
options         MAC_PARTITION
options         MAC_SEEOTHERUIDS
device          npx
device          apic
device          acpi
device          pmtimer
device          atkbdc
device          atkbd
device          psm
device          vga
device          sc
device          sio
device          speaker
device          fdc
device          hwpmc
device          isa
device          pci
device          ata
device          atadisk
device          atapicd
options         ATA_STATIC_ID
device          scbus
device          da
device          pass
device          atapicam
device          cd
device          miibus
device          fxp
device          em
device          usb
device          uhci
device          ohci
device          ehci
device          uhid
device          ukbd
device          ums
device          umass
device          ulpt
device          ucom
device          uplcom
device          md
device          loop
device          mem
device          io
device          random
device          ether
device          vlan
device          gif
device          gre
device          tun
device          tap
device          disc
device          bpf
device          pf
device          pflog
device          pty
device          snp
-- and here --

    VFS is tuned to
vfs.read_max=16
vfs.ufs.dirhash_mem=1048576
vfs.ufs.dirhash_maxmem=67108864

     What else can I do to help narrow down the origin of these crashes ?

-- 
If it's there, and you can see it, it's real.
If it's not there, and you can see it, it's virtual.
If it's there, and you can't see it, it's transparent.
If it's not there, and you can't see it, you erased it.