Experimental ttwwakeup() panic patch

[Doug White]

Hey folks,

I've taken a crack at working around the ttwwakeup() panic thats been
reported now and again.  My early analysis, based on debugging output from
rwatson, is that a defunct struct tty gets reused without cleaning out the
associated (stale) knote structures, and the ttwwakeup() at the end of
sioopen() jumps off into space when it finds them.

This patch is against RELENG_5 but the logic should apply to -CURRENT,
although the patch likely won't as ttymalloc() is organized differently
there.

I did some basic testing on my UP box and didn't see any abberant behavior
afterwards. However I can't reproduce the panic in question, so if you're
good at triggering the panic give this a spin.

http://people.freebsd.org/~dwhite/tty.c.20050503.patch

-- 
Doug White                    |  FreeBSD: The Power to Serve
dwhite at gumbysoft.com          |  www.FreeBSD.org