Just got this from post-UBC kernel while rebuilding its pre-UBC userland. The frames
#0 .. #11 are panic: softdep_lock: locking against myself from vfs_shutdown(). Any
ideas, coredump is available.

#12 0xc014b7e1 in panic () at /sys/kern/subr_prf.c:240
#13 0xc0240c2b in softdep_pageiodone (bp=0xc07aab60) at /sys/ufs/ffs/ffs_softdep.c:5022
#14 0xc016fd64 in genfs_putpages (v=0xcf65555c) at /sys/miscfs/genfs/genfs_vnops.c:1048
#15 0xc0267be3 in uvn_put (uobj=0xcf918288, pps=0xcf655624, npages=2, flags=35)
    at /sys/sys/vnode_if.h:1597
#16 0xc0263dd5 in uvm_pager_put (uobj=0xcf918288, pg=0xc04b7480, ppsp_ptr=0xcf65561c, 
    npages=0xcf655620, flags=35, start=49152, stop=57344) at /sys/uvm/uvm_pager.c:490
#17 0xc0267787 in uvn_flush (uobj=0xcf918288, start=49152, stop=57344, flags=3)
    at /sys/uvm/uvm_vnode.c:601
#18 0xc02509e1 in ufs_balloc_range (vp=0xcf918288, off=49152, len=8192, cred=0xc0824384, flags=3)
    at /sys/ufs/ufs/ufs_inode.c:281
#19 0xc02439ec in ffs_write (v=0xcf655c58) at /sys/ufs/ufs/ufs_readwrite.c:287
#20 0xc01f8878 in nfsrv_write (nfsd=0xc0824300, slp=0xc0754a00, procp=0xcf518e58, mrq=0xcf655df0)
    at /sys/sys/vnode_if.h:386
can not access 0x804b3a0, invalid translation (invalid PDE)
can not access 0x804b3a0, invalid translation (invalid PDE)
can not access 0x804b3a0, invalid translation (invalid PDE)
can not access 0x804b3a0, invalid translation (invalid PDE)
#21 0xc0212447 in nfssvc_nfsd (nsd=0xcf655e50, argp=0x804b3a0 <Address 0x804b3a0 out of bounds>, 
    p=0xcf518e58) at /sys/nfs/nfs_syscalls.c:632
#22 0xc0211bab in sys_nfssvc (p=0xcf518e58, v=0xcf655f88, retval=0xcf655f80)
    at /sys/nfs/nfs_syscalls.c:329
#23 0xc02751ec in syscall (frame={tf_es = 31, tf_ds = 31, tf_edi = -1077945024, tf_esi = 0, 
      tf_ebp = -1077945012, tf_ebx = 0, tf_edx = 1208924096, tf_ecx = 0, tf_eax = 155, 
      tf_trapno = 3, tf_err = 2, tf_eip = 1208619427, tf_cs = 23, tf_eflags = 642, 
      tf_esp = -1077945348, tf_ss = 31, tf_vm86_es = 0, tf_vm86_ds = 0, tf_vm86_fs = 0, 
      tf_vm86_gs = 0}) at /sys/arch/i386/i386/trap.c:734
#24 0xc0100f31 in syscall1 ()
can not access 0xbfbfdd4c, invalid translation (invalid PDE)
can not access 0xbfbfdd4c, invalid translation (invalid PDE)
Cannot access memory at address 0xbfbfdd4c.

-- 
Juergen Hannken-Illjes - hannken@eis.cs.tu-bs.de - TU Braunschweig (Germany)