Panic unloading if_ath

I am seeing this on the relatively regular basis if I am trying to
unload if_ath. System is CURRENT as of September 20th and Atheros part
is 

ath0: <Atheros 5212> mem 0xedf00000-0xedf0ffff irq 17 at device 0.0 on
pci3

Unfortunately, I do not have 100% reliable way to reproduce it, but
approximate scenario is as follows:
-- Network becomes unresponsive
-- I am setting roaming to DEVICE (I should make it a habit of doing it
right after boot, because this setting is not picked up from rc.conf,
but occasionally I forget).
-- when the step above does not work, I try to kldunload if_ath.

Network interface is configured with the static address using
wpa_supplicant with two networks with the same priority visible at the
same time.

If there is any additional information, I can provide, please, let me
know.

Unread portion of the kernel message buffer:
<5>ath0: link state changed to DOWN
kernel trap 12 with interrupts disabled


Fatal trap 12: page fault while in kernel mode
cpuid = 1; apic id = 01
fault virtual address   = 0x188
fault code              = supervisor read, page not present
instruction pointer     = 0x20:0xc04ff0a5
stack pointer           = 0x28:0xe38859d8
frame pointer           = 0x28:0xe38859f0
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = resume, IOPL = 0
current process         = 908 (wpa_supplicant)
trap number             = 12
panic: page fault
cpuid = 1
Uptime: 22h34m46s
Physical memory: 2030 MB
Dumping 213 MB: 198 182 166 150 134 118 102 86 70 54 38 22 6

#0  doadump () at pcpu.h:195
195     pcpu.h: No such file or directory.
        in pcpu.h
(kgdb) bt
#0  doadump () at pcpu.h:195
#1  0xc050b1b7 in boot (howto=260)
at /usr/src/sys/kern/kern_shutdown.c:409
#2  0xc050b4ab in panic (fmt=Variable "fmt" is not available.
) at /usr/src/sys/kern/kern_shutdown.c:563
#3  0xc06c8293 in trap_fatal (frame=0xe3885998, eva=392)
    at /usr/src/sys/i386/i386/trap.c:872
#4  0xc06c8bd1 in trap (frame=0xe3885998)
at /usr/src/sys/i386/i386/trap.c:277
#5  0xc06aee8b in calltrap () at /usr/src/sys/i386/i386/exception.s:139
#6  0xc04ff0a5 in _mtx_lock_sleep (m=0xc4e4e10c, tid=3301954624,
opts=0, 
    file=0xc5642f2c "/usr/src/sys/modules/ath/../../dev/ath/if_ath.c", 
    line=2215) at /usr/src/sys/kern/kern_mutex.c:360
#7  0xc04ff4d2 in _mtx_lock_flags (m=0xc4e4e10c, opts=0, 
    file=0xc5642f2c "/usr/src/sys/modules/ath/../../dev/ath/if_ath.c", 
    line=2215) at /usr/src/sys/kern/kern_mutex.c:186
#8  0xc56398d1 in ?? ()
#9  0xc4e4e10c in ?? ()
#10 0x00000000 in ?? ()
#11 0xc5642f2c in ?? ()
#12 0x000008a7 in ?? ()
#13 0xe3885a38 in ?? ()
#14 0xc0865408 in ?? ()
#15 0xc565d22c in ?? ()
#16 0x00000014 in ?? ()
#17 0xca5e80e0 in ?? ()
#18 0xe3885b28 in ?? ()
#19 0xc086ff4f in ?? ()
#20 0xc565d22c in ?? ()
#21 0xc565e4a4 in ?? ()
#22 0x00000007 in ?? ()
#23 0xc0513b96 in mi_switch (flags=Variable "flags" is not available.
) at /usr/src/sys/kern/kern_synch.c:442
Previous frame inner to this frame (corrupt stack?)
(kgdb) bt
#0  doadump () at pcpu.h:195
#1  0xc050b1b7 in boot (howto=260)
at /usr/src/sys/kern/kern_shutdown.c:409
#2  0xc050b4ab in panic (fmt=Variable "fmt" is not available.
) at /usr/src/sys/kern/kern_shutdown.c:563
#3  0xc06c8293 in trap_fatal (frame=0xe3885998, eva=392)
    at /usr/src/sys/i386/i386/trap.c:872
#4  0xc06c8bd1 in trap (frame=0xe3885998)
at /usr/src/sys/i386/i386/trap.c:277
#5  0xc06aee8b in calltrap () at /usr/src/sys/i386/i386/exception.s:139
#6  0xc04ff0a5 in _mtx_lock_sleep (m=0xc4e4e10c, tid=3301954624,
opts=0, 
    file=0xc5642f2c "/usr/src/sys/modules/ath/../../dev/ath/if_ath.c", 
    line=2215) at /usr/src/sys/kern/kern_mutex.c:360
#7  0xc04ff4d2 in _mtx_lock_flags (m=0xc4e4e10c, opts=0, 
    file=0xc5642f2c "/usr/src/sys/modules/ath/../../dev/ath/if_ath.c", 
    line=2215) at /usr/src/sys/kern/kern_mutex.c:186
#8  0xc56398d1 in ?? ()
#9  0xc4e4e10c in ?? ()
#10 0x00000000 in ?? ()
#11 0xc5642f2c in ?? ()
#12 0x000008a7 in ?? ()
#13 0xe3885a38 in ?? ()
#14 0xc0865408 in ?? ()
#15 0xc565d22c in ?? ()
#16 0x00000014 in ?? ()
#17 0xca5e80e0 in ?? ()
#18 0xe3885b28 in ?? ()
#19 0xc086ff4f in ?? ()
#20 0xc565d22c in ?? ()
#21 0xc565e4a4 in ?? ()
#22 0x00000007 in ?? ()
#23 0xc0513b96 in mi_switch (flags=Variable "flags" is not available.
) at /usr/src/sys/kern/kern_synch.c:442
(kgdb) 

-- 
Alexandre "Sunny" Kovalenko