ehci panic

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

With NetBSD-current/amd64 of yesterday's CVS, I can reproducibly panic ehci
by reading from /dev/video0. (As it's a laptop with no serial card, the
backtrace is abbreviated)

panic: kernel diagnostic assertion "mutex_owned(&sc->sc_lock)" failed: file 
"../../../../dev/usb/ehci.c", line 2895
cpu1: Begin traceback...
kern_assert()
ehci_device_isoc_start()
usbd_transfer()
uvideo_start_transfer()
videoread()
cdev_read()
spec_read()
VOP_READ()
vn_read()
dofileread()
sys_read()
syscall()

sync dumps core, but savecore doesn't find it...

assertion is at start of ehci_alloc_itd() which is called from
ehci_device_isoc_start()

ehci0 at pci0 dev 26 function 0: Intel 6 Series USB (rev. 0x04)
ehci0: interrupting at ioapic0 pin 16
ehci0: EHCI version 1.0
usb0 at ehci0: USB revision 2.0
uhub0 at usb0: Intel EHCI root hub, class 9/0, rev 2.00/1.00, addr 1
uhub0: 3 ports with 3 removable, self powered
uhub2 at uhub0 port 1: vendor 0x8087 product 0x0024, class 9/0, rev 2.00/0.00, 
addr 2
uhub2: single transaction translator
uhub2: 6 ports with 6 removable, self powered
uvideo0 at uhub2 port 5 configuration 1 interface 0: XZB2Q05X 2SF001, rev 
2.00/12.13, addr 4
video0 at uvideo0: XZB2Q05X 2SF001, rev 2.00/12.13, addr 4

Any idea where to look?

Cheers,

Patrick