ata_dmasetup: transfer active on this device!

Bumped into this panic on a kernel from Oct 4 running on my notebook. 
Unfortunately, I don't have a good trace because I didn't have access to a
serial console, or a debugging kernel :-(.  It might well already be
fixed, but I figured I'd post about it just in case.  Basically, I was
shutting down my notebook, and did a "shutdown -p NOW".  During the
shutdown, the system panicked. 

panic: ata_dmasetup: transfer active on this device!
...
ata_dmastart+0x26
ata_pci_dmastart+0x29
ata_transaction+0x999
ata_start+0x1c9
ata_completed+0x230
taskqueue_run+...

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert_at_fledge.watson.org      Network Associates Laboratories