How to Fix Kernel Panic When Lock Held During Page Fault for Command-Line Loaded bce Module?

I'm building the "bce" driver as a module and loading/unloading
it from the command-line to do some work on the driver.  A recent
change to the driver on -CURRENT (v1.25) has introduced the 
following kernel panic:

------------------------------------------------------------------

===[root] /usr/src/sys/modules/bce # make load
/sbin/kldload -v /usr/src/sys/modules/bce/if_bce.ko
bce0: <Broadcom NetXtreme II BCM5708 1000Base-T (B1), v0.9.6> mem
0xdc000000-0xddffffff irq 16 at device 0.0 on pci2
bce0: ASIC ID 0x57081010; Revision (B1); PCI-X 64-bit 133MHz
bce0: Ethernet address: 00:10:18:15:f3:e0
bce0: [ITHREAD]
Kernel page fault with the following non-sleepable locks held:
exclusive sleep mutex bce0 (network driver) r = 0 (0xffffffff8133e068)
locked _at_ /usr/src/sys/modules/bce/../../dev/bce/if_bce.c:774
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
kdb_backtrace() at kdb_backtrace+0x37
witness_warn() at witness_warn+0x2c1
trap() at trap+0x13f
calltrap() at calltrap+0x8
--- trap 0xc, rip = 0xffffffffb07a79c3, rsp = 0xffffffffb079d840, rbp =
0xffffffffb079d860 ---
bce_ifmedia_upd_locked() at bce_ifmedia_upd_locked+0x23
bce_mgmt_init_locked() at bce_mgmt_init_locked+0x99
bce_attach() at bce_attach+0x90f
device_attach() at device_attach+0x5a
device_probe_and_attach() at device_probe_and_attach+0xfe
pci_driver_added() at pci_driver_added+0xf3
devclass_add_driver() at devclass_add_driver+0xfb
driver_module_handler() at driver_module_handler+0x8e
module_register_init() at module_register_init+0x99
linker_file_sysinit() at linker_file_sysinit+0xaf
linker_load_file() at linker_load_file+0x134
linker_load_module() at linker_load_module+0x110
kern_kldload() at kern_kldload+0xb9
kldload() at kldload+0x68
syscall() at syscall+0x307
Xfast_syscall() at Xfast_syscall+0xab
--- syscall (304, FreeBSD ELF64, kldload), rip = 0x80068d24c, rsp =
0x7fffffffeb78, rbp = 0x7fffffffebf0 ---


Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0x38
fault code              = supervisor read data, page not present
instruction pointer     = 0x8:0xffffffffb07a79c3
stack pointer           = 0x10:0xffffffffb079d840
frame pointer           = 0x10:0xffffffffb079d860
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 672 (kldload)
[thread pid 672 tid 100071 ]
Stopped at      bce_ifmedia_upd_locked+0x23:    cmpl    $0,0x38(%rax)

------------------------------------------------------------------

The important lines being:

Kernel page fault with the following non-sleepable locks held:
exclusive sleep mutex bce0 (network driver) r = 0 (0xffffffff8133e068)
locked _at_ /usr/src/sys/modules/bce/../../dev/bce/if_bce.c:774

Why does this problem only occur when loading a module from the 
command-line and what's the right way to fix it?

David Christensen