panic: Journal overflow

This is a i386 current SMP box as of Apr 14 or 15. Got
a panic with geom journal.

panic: Journal overflow (joffset=3246704015360 active=3246705852416 inactive=324
cpuid = 2
KDB: stack backtrace:
db_trace_self_wrapper(c06b3e2c,e5321944,c04fc86e,c06c70c8,2,...) at db_trace_sel
kdb_backtrace(c06c70c8,2,c06ad0d2,e5321950,5,...) at kdb_backtrace+0x2f
panic(c06ad0d2,eea3b800,2f3,eebfc000,2f3,...) at panic+0x11f
g_journal_check_overflow(c4fc5c00,cb030a00,eb,95428000,eb,...) at g_journal_chec
g_journal_flush(c4fc5c00,0,eb,95428000,eb,...) at g_journal_flush+0x60d
g_journal_add_current(c4fc5c00,c9cb0948,ca8e818c,c4fc5c00,e5321cbc,...) at g_jou
g_journal_release_delayed(c4fc5c00,0,ca8e818c,c4fdadc0,2,...) at g_journal_relea
g_journal_flush_send(c4fc5c00,c8521c60,205d0000,1b2,205d4000,...) at g_journal_f
g_journal_worker(c4fc5c00,e5321d38,0,0,0,...) at g_journal_worker+0x7f7
fork_exit(c04b5813,c4fc5c00,e5321d38) at fork_exit+0x83
fork_trampoline() at fork_trampoline+0x8
--- trap 0, eip = 0, esp = 0xe5321d70, ebp = 0 ---

Sorry, that I don't have core dump available. Will set up next time.
After the panic, the system hangs at single user prompt:

Trying to mount root from ufs:/dev/da0s1a
WARNING: / was not properly dismounted
Loading configuration files.
kernel dumps on /dev/da0s1b
Entropy harvesting: interrupts ethernet point_to_point kickstart.
swapon: adding /dev/da0s1b as swap device
Starting file system checks:
/dev/da0s1a: 1704 files, 56880 used, 196935 free (631 frags, 24538 blocks, 0.2%
Can't stat /dev/concat/data.journal: No such file or directory
/dev/da0s1f: 237 files, 1208 used, 11877856 free (64 frags, 1484724 blocks, 0.0%
GEOM_JOURNAL: Journal concat/data consistent.
/dev/da0s1e: UNREF FILE I=548536  OWNER=root MODE=100644
/dev/da0s1e: SIZE=717466 MTIME=Apr  4 07:58 2007  (CLEARED)
/dev/da0s1e: FREE BLK COUNT(S) WRONG IN SUPERBLK (SALVAGED)
/dev/da0s1e: SUMMARY INFORMATION BAD (SALVAGED)
/dev/da0s1e: BLK(S) MISSING IN BIT MAPS (SALVAGED)
/dev/da0s1e: 190105 files, 763850 used, 2281197 free (36557 frags, 280580 blocks
/dev/da0s1d: 17507 files, 40158 used, 972857 free (641 frags, 121527 blocks, 0.1
THE FOLLOWING FILE SYSTEM HAD AN UNEXPECTED INCONSISTENCY:
        ufs: /dev/concat/data.journal (/data)
Unknown error; help!
AEnter full pathname of shell or RETURN for /bin/sh:
# mount -a
WARNING: R/W mount of /backup denied.  Filesystem is not clean - run fsck
mount: /dev/concat/data.journal : Operation not permitted
# fsck_ffs -p /dev/concat/data.journal

I need to issue 'fsck_ffs -p' myself... any idea about why this happens?

The geom journal setup:

Geom name: gjournal 68372861
ID: 68372861
Providers:
1. Name: concat/data.journal
   Mediasize: 3246137539072 (3.0T)
   Sectorsize: 512
   Mode: r1w1e1
Consumers:
1. Name: concat/data
   Mediasize: 3247211281408 (3.0T)
   Sectorsize: 512
   Mode: r1w1e1
   Jend: 3247211280896
   Jstart: 3246137539072
   Role: Data,Journal

The gconcat consists two scsi disk (actually, it's raid) da0 and da1.
Oh no, it panics with journal overflow again while writing this message :(

The data.journal is shared by nfs, and there are two boxes that are
doing a tar writing operation on this partition.

Regards,
Rong-En Fan