Panic upon plugging an USB flash drive into the machine

[Rumko]

I have several USB ports on my chassis, out of which 2 are not connected to the
mainboard ... I plugged an USB drive in one of the ports, there was nothing
in /var/log/messages, so I figured that port was not connected. After that I
unplugged the USB drive and plugged it into another port, upon which a panic
occured. Dump is located at leaf:~rumko/crash/usb/{kernel,vmcore}.0

# kgdb kernel.0 vmcore.0

Unread portion of the kernel message buffer:


GNU gdb 6.7.1
Copyright (C) 2007 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".
(kgdb) bt
#0  dumpsys () at ./machine/thread.h:83
#1  0xc02874e9 in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:376
#2  0xc02877ae in panic (fmt=0xc05007b0 "%s")
at /usr/src/sys/kern/kern_shutdown.c:801
#3  0xc04b4a59 in trap_fatal (frame=0xdc985c00, eva=<value optimized out>)
at /usr/src/sys/platform/pc32/i386/trap.c:1111
#4  0xc04b4b93 in trap_pfault (frame=0xdc985c00, usermode=0, eva=33554706)
at /usr/src/sys/platform/pc32/i386/trap.c:1012
#5  0xc04b51b1 in trap (frame=0xdc985c00)
at /usr/src/sys/platform/pc32/i386/trap.c:692
#6  0xc04a2ee7 in calltrap ()
at /usr/src/sys/platform/pc32/i386/exception.s:785
#7  0xc042d258 in usb_allocmem (bus=0xdc952cc0, size=4, align=0, p=0xc5c2c9fc)
at /usr/src/sys/bus/usb/usb_mem.c:249
#8  0xc0421f2d in ehci_allocm (bus=0xdc952cc0, dma=0xc5c2c9fc, size=4)
at /usr/src/sys/bus/usb/ehci.c:1017
#9  0xc042ba1e in usbd_transfer (xfer=0xc5c2c9c0)
at /usr/src/sys/bus/usb/usbdi.c:299
#10 0xc042bc10 in usbd_sync_transfer (xfer=0xc5c2c9c0)
at /usr/src/sys/bus/usb/usbdi.c:343
#11 0xc042bc70 in usbd_do_request_flags_pipe (dev=0xd8fcdec0, pipe=0xc5b86e98,
req=0xdc985d24, data=0xc5cfc5e4, flags=0, actlen=0x0, timeout=5000)
    at /usr/src/sys/bus/usb/usbdi.c:954
#12 0xc042bde7 in usbd_do_request_flags (dev=0xd8fcdec0, req=0xdc985d24,
data=0xc5cfc5e4, flags=0, actlen=0x0, timo=5000)
    at /usr/src/sys/bus/usb/usbdi.c:927
#13 0xc042be03 in usbd_do_request (dev=0xd8fcdec0, req=0xdc985d24,
data=0xc5cfc5e4) at /usr/src/sys/bus/usb/usbdi.c:919
#14 0xc042c5bb in usbd_get_port_status (dev=0xd8fcdec0, port=10, ps=0xc5cfc5e4)
at /usr/src/sys/bus/usb/usbdi_util.c:165
#15 0xc04304e3 in uhub_explore (dev=0xd8fcdec0)
at /usr/src/sys/bus/usb/uhub.c:390
#16 0xc042a9d6 in usb_discover (self=<value optimized out>)
at /usr/src/sys/bus/usb/usb.c:743
#17 0xc042adbe in usb_event_thread (arg=0xc5b86df8)
at /usr/src/sys/bus/usb/usb.c:454
#18 0xc027ac23 in suspend_kproc (td=Cannot access memory at address 0x8
) at /usr/src/sys/kern/kern_kthread.c:158
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
-- 
Regards,
Rumko