(kgdb) bt
#0  doadump () at ../../../kern/kern_shutdown.c:240
#1  0xc04f2bc8 in boot (howto=260) at ../../../kern/kern_shutdown.c:372
#2  0xc04f2f57 in panic () at ../../../kern/kern_shutdown.c:550
#3  0xc0538241 in bremfreel (bp=0xd8f0aab8) at ../../../kern/vfs_bio.c:647
#4  0xc0538115 in bremfree (bp=0x0) at ../../../kern/vfs_bio.c:629
#5  0xc053bd4e in getblk (vp=0xcca14104, blkno=7, size=16384, slpflag=0, slptimeo=0, flags=0)
    at ../../../kern/vfs_bio.c:2468
#6  0xc0538312 in breadn (vp=0xcca14104, blkno=0, size=0, rablkno=0x0, rabsize=0x0, cnt=0, cred=0x0, bpp=0x0)
    at ../../../kern/vfs_bio.c:700
#7  0xc05382bc in bread (vp=0x0, blkno=0, size=0, cred=0x0, bpp=0x0) at ../../../kern/vfs_bio.c:682
#8  0xc05bc352 in ffs_balloc_ufs2 (vp=0xcca14104, startoffset=0, size=5856, cred=0xc25bbe00, flags=65536, 
    bpp=0xea0367b4) at ../../../ufs/ffs/ffs_balloc.c:601
#9  0xc05d30c7 in ffs_write (ap=0xea0367ec) at ../../../ufs/ffs/ffs_vnops.c:698
#10 0xc05dc874 in dqsync (vp=0xccc84b2c, dq=0xcd11a1c0) at vnode_if.h:432
#11 0xc05dc1b0 in qsync (mp=0xcc935800) at ../../../ufs/ufs/ufs_quota.c:775
#12 0xc05d18fd in ffs_sync (mp=0xcc935800, waitfor=2, cred=0xc25b0f00, td=0xc06a48a0)
    at ../../../ufs/ffs/ffs_vfsops.c:1204
#13 0xc054e61e in sync (td=0xc06a48a0, uap=0x0) at ../../../kern/vfs_syscalls.c:141
#14 0xc04f2760 in boot (howto=256) at ../../../kern/kern_shutdown.c:281
#15 0xc04f2f57 in panic () at ../../../kern/kern_shutdown.c:550
#16 0xc05391f1 in bundirty (bp=0xd90341f0) at ../../../kern/vfs_bio.c:1122
#17 0xc0539d1e in brelse (bp=0xd90341f0) at ../../../kern/vfs_bio.c:1441
#18 0xc05915a8 in nfs_writebp (bp=0xd90341f0, force=1, td=0xccd77640) at ../../../nfsclient/nfs_vnops.c:2990
#19 0xc0581bc3 in nfs_bwrite (bp=0x0) at machine/pcpu.h:156
#20 0xc053be11 in getblk (vp=0xccd54c30, blkno=1, size=8192, slpflag=0, slptimeo=0, flags=0)
    at ../../../kern/vfs_bio.c:2536
#21 0xc0583c24 in nfs_getcacheblk (vp=0xccd54c30, bn=1, size=8192, td=0xccd77640)
    at ../../../nfsclient/nfs_bio.c:1064
#22 0xc0583780 in nfs_write (ap=0x0) at ../../../nfsclient/nfs_bio.c:874
#23 0xc0557393 in vn_write (fp=0xcc997f68, uio=0xea036c80, active_cred=0xcdbc9700, flags=0, td=0xccd77640)
    at vnode_if.h:432
#24 0xc05198fb in dofilewrite (td=0xccd77640, fp=0xcc997f68, fd=0, buf=0x879a000, nbyte=0, offset=0, flags=0)
    at ../../../sys/file.h:249
#25 0xc051972e in write (td=0xccd77640, uap=0xea036d14) at ../../../kern/sys_generic.c:331
#26 0xc062a3e0 in syscall (frame=
      {tf_fs = 47, tf_es = 47, tf_ds = 47, tf_edi = 142188544, tf_esi = 3, tf_ebp = -1077944360, tf_isp = -368874124, tf_ebx = 673177888, tf_edx = 4096, tf_ecx = 12, tf_eax = 4, tf_trapno = 22, tf_err = 2, tf_eip = 672674095, tf_cs = 31, tf_eflags = 531, tf_esp = -1077944420, tf_ss = 47}) at ../../../i386/i386/trap.c:1010
#27 0xc061b21d in Xint0x80_syscall () at {standard input}:136