Constant crashes on x86_64 with UFS

[Jan Lentfer]

On the VM that I provide for Justin to make bulk builds I am getting 
constant panics after I enabled swapcache.

#14 0xffffffff8035d01f in panic (fmt=0xffffffff80685d46 "ffs_realloccg: 
bad blockno") at /usr/src/sys/kern/kern_shutdown.c:785
#15 0xffffffff804fec9c in ffs_realloccg (ip=0xffffffe00096e698, 
lbprev=<value optimized out>, bpref=8, osize=4096, nsize=5120,
    cred=0xffffffe000886900, bpp=0xffffffe02e4157f0) at 
/usr/src/sys/vfs/ufs/ffs_alloc.c:230
#16 0xffffffff804ff338 in ffs_balloc (ap=0xffffffe02e415838) at 
/usr/src/sys/vfs/ufs/ffs_balloc.c:183
#17 0xffffffff803cece0 in vop_balloc (ops=0xffffffe007fcea80, 
vp=0xffffffe02e58b400, startoffset=<value optimized out>, size=<value 
optimized out>,
    cred=<value optimized out>, flags=<value optimized out>, 
bpp=0xffffffe02e415918) at /usr/src/sys/kern/vfs_vopops.c:936
#18 0xffffffff8050abba in ffs_write (ap=0xffffffe02e415958) at 
/usr/src/sys/vfs/ufs/ufs_readwrite.c:348
#19 0xffffffff803cf738 in vop_write (ops=0xffffffe007fcea80, 
vp=0xffffffe02e58b400, uio=<value optimized out>, ioflag=<value 
optimized out>,
    cred=<value optimized out>) at /usr/src/sys/kern/vfs_vopops.c:427
#20 0xffffffff803cdb7b in vn_write (fp=0xffffffe00ab7d4a8, 
uio=0xffffffe02e415ad8, cred=0xffffffe000886900, flags=<value optimized 
out>)
    at /usr/src/sys/kern/vfs_vnops.c:724
#21 0xffffffff803871ef in dofilewrite (fd=6, auio=0xffffffe02e415ad8, 
flags=0, res=0xffffffe02e415b48) at /usr/src/sys/sys/file2.h:72

Kernel is
DragonFly df64pkgbuilder.lan.net 2.9-DEVELOPMENT DragonFly 
v2.9.0.116.ge61a8-DEVELOPMENT #0: Fri Nov  5 06:38:41 CET 2010 
root at df64pkgbuilder.lan.net:/usr/obj/usr/src/sys/X86_64_GENERIC  x86_64

Anyone seen this before?

Jan