Re: 2.6.14-rc4-rt1 - enable IRQ-off tracing causes kernel to fault at boot

From: Ingo Molnar
Date: Thu Oct 13 2005 - 22:56:10 EST

* Mark Knecht <markknecht@xxxxxxxxx> wrote:

> Ingo & Steve,
> Thank you for your great instructions that even a guitar player
> could basically follow. After about an hour of messing around I did
> manage to capture the crash. The console file is attached.
> NOTE: The first time I booted the kernel it got to the crash point and
> the machine rebooted. The second time it booted I got the trace. Both
> boots are in the capture file.

thanks, this log is much more informative. No smoking gun though, but it
seems something fundamental (probably lowlevel x64 code) has been broken
by -rt1.

Do the crashes go away if you take the -rc3-rt13 version of
arch/x86_64/kernel/entry.S and copy it over into the -rc4-rt1 tree?
[this undoes a particular set of CONFIG_CRITICAL_IRQSOFF_TIMING fixes
from the x64 code, which i did during -rc3-rt13 => -rc4-rt1]

(Note that doing this will re-introduce tracing bugs, which can result
in false-positive latency readings - but it should fix any related
lowlevel bug in the assembly code.)

if this indeed solves the crash then i'd suggest to restore the -rt1
version of entry.S, and i'd suggest to disable CRITICAL_IRQSOFF_TIMING
until i fix it. You should be able to get pretty good latency tracing
info even without CRITICAL_IRQSOFF_TIMING.

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