From owner-freebsd-current  Tue Dec  3  7:35:52 2002
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From: "Long, Scott" <Scott_Long@adaptec.com>
To: "'Chuck Robey'" <chuckr@chuckr.org>,
	Manfred Antar <null@pozo.com>
Cc: kalts@estpak.ee, FreeBSD-current <current@FreeBSD.ORG>
Subject: RE: console problem
Date: Tue, 3 Dec 2002 10:35:37 -0500 
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> It's not the fact that I have an extra, unused on-board video 
> (checked).
> Also, when the video output stops, the console still works 
> fine for input
> (keyboard never stops working normally).  Also, I can 
> successfully start X
> just fine.  It's just the vty's output that is stopped (all 
> vtys, alt-Fn
> has no effect on output, only input).  It's not wiped, just no further
> changes.  I tried issuing a vidcontrol; before lockup, color 
> change works
> fine, after, no effect.
> 
> It's acting as if the mapping in memory to the video buffer 
> has changed.
> 

The problem is that the syscons driver stops updating the 
display because it's timeout call to scrn_timeout() gets
lost and/or never re-armed.  The causes could be one or
more of the following:

1) a race in the syscons code that determines whether or not
to re-arm the periodic timeout.
2)  a race in the callout code that results in random timeouts
getting lost.  Since syscons timeout happens 10 times a second,
it has a high chance of being affected.
3) breakage in softclock, resulting in timeouts not being
triggered at all.  I highly doubt this one since the rest of the
machine works fine.

Note that while it happens easily on SMP machines, I was able to
trigger it last night on a UP box in the form of the syscons bell
getting turned on but not off.

My SMP box died while trying to debug this and I haven't been able to
get access to another one yet.  If anyone is interested in looking
at it, /sys/dev/syscons/syscons.c:scrn_timeout() is a good place
to start.

Scott

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