Bug 4715

Distribution: I got the sources from
http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.11.11.tar.bz2 


Hardware Environment: Pentium-M/Motherboard:DFI-ACP-G5M100-N
rev1/Modem:Intracom's netmod ver5.0 firmware 3.83

Software Environment: Debian custom based on potato
Problem Description: I try to set-up ppp using a ACM usb ISDN modem. It start ok
but If I (usb unplug/modem losses power/modem losses link) the kernel crashes.

Steps to reproduce:
Compile kernel with USB ACM support
create dir /dev/usb/acm
mknod /dev/usb/acm/ttyACM0 c 166 0
put in /etc/inittab
mgetty /dev/usb/acm/ttyACM0
plugin the modem 
initq or reboot
System comes up  
It will be able to answer calls.
Now...
Unplug the usb cable from Modem and the kernel will crash.
Unplug the Main Power from the Modem and the kernel will crash.
Unplug the telephone line from the Modem and the kernel will crash.