kern/39793: crash on umass disconnect

[hramrach%centrum.cz@localhost]

>Number:         39793
>Category:       kern
>Synopsis:       crash on umass disconnect
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Oct 24 10:25:00 +0000 2008
>Originator:     Michal Suchanek
>Release:        4.0.1
>Organization:
>Environment:
i386
>Description:
I tried to install NetBSD on an USB drive connected to a miniMac.

During installation the kernel panicked in some usb driver memory allocation 
routine.

I tried to install Linux instead, and it turned out the device is flaky and 
disconnects after some time of heavy IO and irregular(such as during system 
install).

I did not try to reproduce the bug but I recall NetBSD having trouble with 
umass devices disconnected while in use.
>How-To-Repeat:
mount an umass device and disconnect it
>Fix: