Turning off USB drives causes panics

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Hi!

I was backing up to an external USB drive:

umass1 at uhub4 port 4 configuration 1 interface 0
umass1: vendor 0x05e3 USB Storage, rev 2.00/97.27, addr 7
umass1: using SCSI over Bulk-Only
scsibus1 at umass1: 2 targets, 5 luns per target
sd0: GPT GUID: some-guid
dk10 at sd0: some name

when I accidentally cut power to the drive, which lead to a panic:

kernel diagnostic assertion "vp == vp->v_specnode->sn_dev->sd_bdevvp" failed: 
file "/archive/foreign/src/sys/miscfs/specfs/spec_vnops.c", line 1015 

panic in dmesg is nigh unreadable (mixed with "SPL NOT LOWERED ON
TRAP EXIT"), but contains at least the following:

genfs_do_io
genfs_gop_write
genfs_do_putpages
VOP_PUTPAGES
ffs_write
VOP_WRITE
vn_write
dofilewrite
sys_write
syscall

I know it's not smart to turn off the disk while writing to it :)

Is there a way to make NetBSD not panic for something like that,
though?
 Thomas