Re: 2.6.3 Heisenbug in unwind.c

From: David Mosberger <>
Date: 2004-02-25 01:29:45
>>>>> On Tue, 24 Feb 2004 23:05:37 +1100, Keith Owens <> said:

  Keith> I am seeing a Heisenbug in the 2.6.3 kernel unwind code.  The
  Keith> symptoms are that the backtrace terminates early, usually
  Keith> failing to unwind past an interrupt frame.

I haven't seen that in quite some time.

  Keith> Andreas, this _may_ be what you are seeing.

  Keith> Changing the config options (sn2->dig) makes backtrace work
  Keith> again.  Turning on UNW_DEBUG to debug the unwinder makes
  Keith> backtrace work again :(.  Adding 30 dummy functions (which
  Keith> only call printk and are never called themselves) to unwind.c
  Keith> makes the backtrace work again.

  Keith> That last one really worries me.  All it does is shift the
  Keith> position of the real unwind code within the kernel without
  Keith> changing the unwind code itself.  Looks like an uninitialised
  Keith> pointer somewhere.

  Keith> gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-24) GNU
  Keith> assembler version (ia64-unknown-linux-gnu) using
  Keith> BFD version 20030523

It doesn't sound like a timing-related bug though, which is good news.
If you could reproduce the problem with Ski, that would almosts certainly
make it possible to root-cause it relatively quickly.

It might also be worthwhile to see if gcc 3.3.3 or 3.4 makes any difference.

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Received on Tue Feb 24 09:30:37 2004

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