Re: [stable] Regression in 2.6.32.2: segfault on halt

[Mike Galbraith <efault@gmx.de>]

On Sun, 2009-12-20 at 14:27 +0100, Holger Hoffstätte wrote:

> Took me some time (still learning git - I usually use hg) but I just
> managed to fix it by reverting not the bisected revision (won't compile
> any longer), but the follow-up "cleanup & fix":
> 
> >From 35c1ee3e78766d5666f418af638def9c67e63ecb Mon Sep 17 00:00:00 2001
> From: Mike Galbraith <efault@gmx.de>
> Date: Tue, 10 Nov 2009 03:50:02 +0100
> Subject: [PATCH] sched: Fix and clean up rate-limit newidle code
> 
> commit eae0c9dfb534cb3449888b9601228efa6480fdb5 upstream.
> 
> Commit 1b9508f, "Rate-limit newidle" has been confirmed to fix
> the netperf UDP loopback regression reported by Alex Shi.
> 
> This is a cleanup and a fix:
> 
>  - moved to a more out of the way spot
> 
>  - fix to ensure that balancing doesn't try to balance
>    runqueues which haven't gone online yet, which can
>    mess up CPU enumeration during boot.
> 
> Reported-by: Alex Shi <alex.shi@intel.com>
> Reported-by: Zhang, Yanmin <yanmin_zhang@linux.intel.com>
> Signed-off-by: Mike Galbraith <efault@gmx.de>
> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> LKML-Reference: <1257821402.5648.17.camel@marge.simson.net>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
> 
> aka:
> http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.32.y.git;a=commit;h=35c1ee3e78766d5666f418af638def9c67e63ecb
> 
> Reverting this from a clean 32.2 tree results in a kernel with newidle
> fix, but still working halt/reboot. The only difference between this and
> the bisected one is the additional change in cpumask handling.
> 
> That was more fun than expected :)

Egad.  Reverting the cpumask bit alone cures the problem?

	-Mike