Hi Alan, all,

I added an extra check to the videodev.c's video_ioctl, to check vfl is
valid before dereferencing. (See attached patch).

The sequence to trigger the oops appears to be:

1. Open philips usb webcam device (any usb video device with ioctls ?).
2. Wait for (fairly rare) USB EMI issue to be flagged by hub.c.
3. usb.c appears to force a disconnect immediately after #2.
4. pwc module warns about a disconnect while open.
5. Next call to video_ioctl with handle from #1 causes oops.

I added a check to video_icotl to ensure video_device[] isn't NULL
before trying to call the ioctl method, and it returns EINVAL in that
case.

I'm not very familiar with the locking of usb/usb-uhci in this EMI case,
but both host drivers oops in the same way.  It would seem the open file
handle needs to be disassociated too somehow - or at least 'defered'
until the video camera is re-enabled after the EMI event.

Best regards,

Mark

PS. I've recently changed the physical layout of the machine, and it
seems the new cabling layout causes these occasional EMI issues.

-- 
Mark Cooke <mpc@star.sr.bham.ac.uk>