Kernel Dump when accessing second drive

[Dylan Reinhold <dylan@xxxxxxxxxxxxxxxx>]

I added a second drive, to copy ~100GB's to my machine, but the kernel 
panics when I try and rsync the data.
The second drive is formated ext2 and mounted as readonly.

Here is the backtrace from the kernel dump.

# kgdb kern.0 vmcore.0
GNU gdb (GDB) 7.0
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i386-dragonfly".
For bug reporting instructions, please see:
<http://bugs.dragonflybsd.org/>...
Reading symbols from /var/crash/kern.0...done.

Unread portion of the kernel message buffer:
ad6: FAILURE - device detached
subdisk6: detached
ad6: detached


Fatal trap 12: page fault while in kernel mode
fault virtual address   = 0xa4
fault code              = supervisor write, page not present
instruction pointer     = 0x8:0xc02fec0e
stack pointer           = 0x10:0xca593c78
frame pointer           = 0x10:0xca593c90
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = Idle
current thread          = pri 46 (CRIT)

kernel: type 12 trap, code=2
panic: from debugger


Fatal trap 3: breakpoint instruction fault while in kernel mode
instruction pointer     = 0x8:0xc05445f0
stack pointer           = 0x10:0xca593a88
frame pointer           = 0x10:0xca593a90
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, IOPL = 0
current process         = Idle
current thread          = pri 78 (CRIT)

panic: from debugger
Uptime: 7m59s
Physical memory: 503 MB
Dumping 101 MB: 86 70 54 38 22 6

Reading symbols from /boot/modules/acpi.ko...done.
Loaded symbols for /boot/modules/acpi.ko
Reading symbols from /boot/modules/ext2fs.ko...done.
Loaded symbols for /boot/modules/ext2fs.ko
_get_mycpu (di=0xc06bba20) at ./machine/thread.h:83
83          __asm ("movl %%fs:globaldata,%0" : "=r" (gd) : 
"m"(__mycpu__dummy));
(kgdb) bt
#0  _get_mycpu (di=0xc06bba20) at ./machine/thread.h:83
#1  md_dumpsys (di=0xc06bba20) at 
/usr/src/sys/platform/pc32/i386/dump_machdep.c:264
#2  0xc0317852 in dumpsys () at /usr/src/sys/kern/kern_shutdown.c:838
#3  0xc0317dcd in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:387
#4  0xc0317ef3 in panic (fmt=0xc05a067e "from debugger") at 
/usr/src/sys/kern/kern_shutdown.c:744
#5  0xc01765a5 in db_panic (addr=-1070601202, have_addr=0, count=1, 
modif=0xca593af0 "")
    at /usr/src/sys/ddb/db_command.c:448
#6  0xc0176c1a in db_command () at /usr/src/sys/ddb/db_command.c:344
#7  db_command_loop () at /usr/src/sys/ddb/db_command.c:470
#8  0xc017921c in db_trap (type=12, code=2) at /usr/src/sys/ddb/db_trap.c:71
#9  0xc054475c in kdb_trap (type=12, code=2, regs=0xca593c30) at 
/usr/src/sys/platform/pc32/i386/db_interface.c:152
#10 0xc05562c0 in trap_fatal (frame=0xca593c30, eva=<value optimized 
out>) at /usr/src/sys/platform/pc32/i386/trap.c:1120
#11 0xc0556422 in trap_pfault (frame=0xca593c30, usermode=0, eva=164) at 
/usr/src/sys/platform/pc32/i386/trap.c:1026
#12 0xc05568f4 in trap (frame=0xca593c30) at 
/usr/src/sys/platform/pc32/i386/trap.c:713
#13 0xc0545b37 in calltrap () at 
/usr/src/sys/platform/pc32/i386/exception.s:785
#14 0xc02fec0e in getmicrouptime (tvp=0xa4) at 
/usr/src/sys/kern/kern_clock.c:972
#15 0xc032ef84 in devstat_end_transaction (ds=0x18, bytes=0, 
tag_type=DEVSTAT_TAG_SIMPLE, flags=DEVSTAT_READ)
    at /usr/src/sys/kern/subr_devstat.c:189
#16 0xc032f0ac in devstat_end_transaction_buf (ds=0x18, bp=0xc1f6f5d0) 
at /usr/src/sys/kern/subr_devstat.c:248
#17 0xc01bb669 in ad_done (request=0xc1d6f7e8) at 
/usr/src/sys/dev/disk/nata/ata-disk.c:368
#18 0xc01c0f5c in ata_completed (context=0xc1d6f7e8, dummy=1) at 
/usr/src/sys/dev/disk/nata/ata-queue.c:516
#19 0xc03388cb in taskqueue_run (queue=0xc1bc2010, lock_held=0) at 
/usr/src/sys/kern/subr_taskqueue.c:271
#20 0xc033894c in taskqueue_swi_run (arg=0x0, frame=0x0) at 
/usr/src/sys/kern/subr_taskqueue.c:299
#21 0xc02f8dec in ithread_handler (arg=0x45) at 
/usr/src/sys/kern/kern_intr.c:817
#22 0xc031f306 in lwkt_deschedule_self (td=Cannot access memory at 
address 0x8
) at /usr/src/sys/kern/lwkt_thread.c:248
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
(kgdb)