Bug 18315

Short program causes system to lock-up completely ( no response to any 
keys, can't telnet to it, harddrive light doesn't go off even though 
there's no audible activity, num-lock key doesn't toggle its light).

The program just repeatedly captures an image and writes it to disk,
all in a SIGALRM handler.  If the spacing between the SIGALARM's is made
to be such that the disk writes run together (hard drive light on
continuously), the system locks solid after a few seconds.

This happened with release 3.3 also, I've never tried 3.4.
I have tried it on both a bt848 and a bt878 and have gotten lockups
on both (release 3.3 with bt848 and release 4.0 with bt878).

Note that just repeatedly capturing and reading the buffer 
(and not writing to file), or just repeatedly writing the capture
buffer to file (after only capturing once, initially), does not lead
to a hang.  You have to capture and write repeatedly (close together)
to get the hang.

How-To-Repeat: Assuming you have a bt848/bt878 installed:
Contact me at sch@aristotle.net and I'll send you "lockup.c",
(or tell me where I should have posted it!).
cc -o lockup lockup.c
(save any work and "sync")
./lockup &
wait for the hang