linux-kernel - Re: 2.6.25-rc: complete lockup on boot/start of X (bisected)

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Date:	Sun, 2 Mar 2008 20:47:53 +0100
From:	Marcin Slusarz <marcin.slusarz@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: 2.6.25-rc: complete lockup on boot/start of X (bisected)

On Sun, Mar 02, 2008 at 08:11:11PM +0100, Peter Zijlstra wrote:
> 
> On Sun, 2008-03-02 at 20:00 +0100, Marcin Slusarz wrote:
> > Hi
> > Since early 2.6.25 days I'm having strange lockup on boot. As it happens
> > rarely (in ~10% of boots), I couldn't bisect it. No kernel panic, SysRq
> > didn't work, so I couldn't provide any useful informations to LK community.
> > I hoped someone else would fix it... :)
> > 
> > It's rc3 so I decided to narrow it down myself. I enabled netconsole 
> > to see whether some other informations are printed before lockup.
> > It didn't help, but I noticed that lockup happens much more frequenly! (~50%)
> > So I bisected it down to:
> > 
> > 8f4d37ec073c17e2d4aa8851df5837d798606d6f is first bad commit
> > commit 8f4d37ec073c17e2d4aa8851df5837d798606d6f
> > Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Date:   Fri Jan 25 21:08:29 2008 +0100
> > 
> >     sched: high-res preemption tick
> > 
> >     Use HR-timers (when available) to deliver an accurate preemption tick.
> > 
> >     The regular scheduler tick that runs at 1/HZ can be too coarse when nice
> >     level are used. The fairness system will still keep the cpu utilisation 'fair'
> >     by then delaying the task that got an excessive amount of CPU time but try to
> >     minimize this by delivering preemption points spot-on.
> > 
> >     The average frequency of this extra interrupt is sched_latency / nr_latency.
> >     Which need not be higher than 1/HZ, its just that the distribution within the
> >     sched_latency period is important.
> > 
> >     Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> >     Signed-off-by: Ingo Molnar <mingo@...e.hu>
> > 
> > :040000 040000 ab225228500f7a19d5ad20ca12ca3fc8ff5f5ad1 f1742e1d225a72aecea9d6961ed989b5943d31d8 M      arch
> > :040000 040000 25d85e4ef7a71b0cc76801a2526ebeb4dce180fe ae61510186b4fad708ef0211ac169decba16d4e5 M      include
> > :040000 040000 9247cec7dd506c648ac027c17e5a07145aa41b26 950832cc1dc4d30923f593ecec883a06b45d62e9 M      kernel
> > 
> > I can't revert it on top of rc3 because of conflicts.
> 
> This should do, I guess. Weird though, I haven't had trouble with this
> patch in a long long while. Nor I suppose has Ingo's QA setup.
Ok. It did the trick. But it's temporary fix, right?
 
> Will try if I can reproduce using your .config.
I think this lockup might depend on use of dhcp and/or parallel
starting of services...

> ---
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index b73ee9e..02cbf34 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -741,7 +741,7 @@ const_debug unsigned int sysctl_sched_features =
>  		SCHED_FEAT_NEW_FAIR_SLEEPERS	* 1 |
>  		SCHED_FEAT_WAKEUP_PREEMPT	* 1 |
>  		SCHED_FEAT_START_DEBIT		* 1 |
> -		SCHED_FEAT_HRTICK		* 1 |
> +		SCHED_FEAT_HRTICK		* 0 |
>  		SCHED_FEAT_DOUBLE_TICK		* 0;
>  
>  #define sched_feat(x) (sysctl_sched_features & SCHED_FEAT_##x)
> 
> 
> 
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