Re: Preemption-related bug in propagate_priority(): it's OK to hold Giant but not be running

From: Robert Watson (rwatson_at_freebsd.org)
Date: 10/19/04

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    Date: Tue, 19 Oct 2004 17:53:07 -0400 (EDT)
To: John Baldwin <jhb@freebsd.org>

    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

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