Panic on mount with write-locked USB media (umass)

I have recently been using a USB memory stick. It's a generic device
which only identifies itself as "<USB Flash Drive 1.89> Removable Direct
Access SCSI-2 Device". Works fine.

Then I plugged it in with the write lock switch on and tried to mount
it.  "mount_msdosfs: /dev/da0s1: Permission denied" Hey! I'm root! This
is supposed to work. Sounds like the partitioning and GEOM foot shooting
thread. Oh, well, but this really could be handled better.

I can mount it just fine as long as I do so as read-only, so it's just
annoying. It's what happens if I get stubborn and try to mount it again
without the '-r':
Fatal trap 12: page fault while in kernel mode
fault virtual address   = 0x0
fault code              = supervisor read, page not present
instruction pointer     = 0x8:0xc04b5be3
stack pointer           = 0x10:0xd5668c1c
frame pointer           = 0x10:0xd5668c2c
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         = 48 (syncer)
[thread pid 48 tid 100049 ]
Stopped at      g_io_request+0x13:      pushl   0(%esi)
db> tr
Tracing pid 48 td 0xc19c5960
g_io_request(c2546bdc,c218f3c0,a00000a4,cbf02a80,d5668c5c) at g_io_request+0x13
g_vfs_strategy(c2849850,cbf02a80) at g_vfs_strategy+0x49)
bufwrite(cbf02a80) at bufwrite+0xf4
bawrite(cbf02a80,) at bawrite+0x13
vop_stdfsync(d5668cd0,c284978c,d5668cac,c0660388,d5668cd0) at vop_stdfsync+0x186
devfs_fsync(d5668cd0) at devfs_fsync+0x23
VOP_FSYNC_APV(c06be280,d5668cd0) at VOP_FSYNC_APV+0x38
sync_vnode(c2849850,c19c5960) at sync_vnode+0x14a
sched_sync(0,d5668d48) at shed_sync+0x24d
fork_exit(c054ff4,0,d5668d48) at fork_exit+0x74
fork_trampoline() at fork_trampoline+0x8
--- trap 0x1, eip = 0, esp = 0xd5668d7c, ebp = 0 ---

I can reproduce this at will.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman_at_es.net			Phone: +1 510 486-8634