panic copying ext2fs -> raidframe 1 ffsv2

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

On a -current/amd64 box of 16 Jul 2013, I just mounted some

 f:   1992060   8000370 Linux Ext2      0     0        # (Cyl.   7936*-   9913*)

partitions (using mount_ext2fs, not fuse), and started a copy (cp -a)to
a raid 1
file system: /dev/rraid3a
cylgrp  dynamic inodes  FFSv2   sblock  FFSv2   fslevel 5
flags   wapbl 

Went for a coffee, and came back to find a not very informative panic:

(gdb) bt
#0  0xffffffff804e462e in cpu_reboot (howto=260, bootstr=<optimized out>)
    at ../../../../arch/amd64/amd64/machdep.c:701
#1  0xffffffff80696ced in vpanic (fmt=0xffffffff809f9f75 "trap", 
    ap=0xfffffe8115fc63c0) at ../../../../kern/subr_prf.c:284
#2  0xffffffff80696da1 in panic (fmt=<unavailable>)
    at ../../../../kern/subr_prf.c:200
#3  0xffffffff806e1ad8 in trap (frame=0xfffffe8115fc64e0)
    at ../../../../arch/amd64/amd64/trap.c:294
#4  0xffffffff8010100e in alltraps ()
#5  0xfffffe8115fc6610 in ?? ()
#6  0xfffffe8115fc666f in ?? ()
#7  0x0000000000000006 in ?? ()
#8  0x0000000000000000 in ?? ()

(this is a DEBUG DIAGNOSTIC LOCKDEBUG UVMHIST kernel)

Any thoughts about the filesystems / ways of getting better backtraces?

Cheers,

Patrick