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Date: Tue, 19 Oct 2004 17:53:07 -0400 (EDT)
From: Robert Watson <rwatson@freebsd.org>
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To: John Baldwin <jhb@freebsd.org>
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cc: Julian Elischer <julian@elischer.org>
Subject: Re: Preemption-related bug in propagate_priority(): it's OK to hold
	Giant but not be running
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On Tue, 19 Oct 2004, John Baldwin wrote:

> > it would be relatively simple to put those 'discarded' threads onto a
> > single list in the kernel
> > and 'c' could put them back on the run queue :-)
> 
> That's a really nasty hack.  I almost wonder if we shouldn't just bump
> the priority of the thread that panics way up instead, or maybe use a
> dedicated thread for handling panics or something. 

I have to admit I was somewhat surprised to see that a thread was
preempted during a panic.  I had sort of assumed that as we panicked we
disabled interrupts, since the I/O for the debugger is polled, etc.

Speaking of which, I've seen a number of bug reports that suggest our
polled debugger I/O interfaces for the low level console are not
implemented properly by syscons (and maybe also sio), resulting in
unnecessary debugging complications (running wakeup() while in DDB and so
on).

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Principal Research Scientist, McAfee Research