The anti user-DoS mechanism in the USB serial 'visor' driver can fail in
the following way:

visor_open: priv->outstanding_urbs = 0
visor_write: ++priv->outstanding_urbs
visor_close:
visor_open: priv->outstanding_urbs = 0
visor_write_bulk_callback: --priv->outstanding_urbs

So priv->outstanding_urbs ends up as (unsigned long)(-1).  Not good!

I haven't seen this happen with the visor driver as I don't have the
hardware, but I have seen it while testing a patch to implement the same
functionality in the ftdi_sio driver (patch not yet submitted).

The fix is pretty simple: don't reinitialize outstanding_urbs in
visor_open.  (Again, I haven't tested the fix in visor, but I have
tested it in ftdi_sio.)
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>