linux-kernel - Re: 2.6.21-rc7-mm2 hangs in boot (netconsole)

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Message-Id: <20070501091538.c14b1cf9.randy.dunlap@oracle.com>
Date:	Tue, 1 May 2007 09:15:38 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.21-rc7-mm2 hangs in boot (netconsole)

On Mon, 30 Apr 2007 22:38:59 -0700 Andrew Morton wrote:

> On Tue, 1 May 2007 08:24:56 +0200 Andi Kleen <ak@...e.de> wrote:
> 
> > > The bug is in firstfloor only, and the fix (if present) will be there too.
> > > 
> > > <checks>
> > > 
> > > Nope,
> > > 
> > > ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/sched-clock-share
> > > 
> > > is identical to
> > > 
> > > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.21-rc7/2.6.21-rc7-mm2/broken-out/x86_64-mm-sched-clock-share.patch
> > 
> > Or perhaps the deadlock is in the cpufrequency handler. Does it happen without CONFIG_CPUFREQ
> > too?
> > 
> > [cpufreq handler calls ktime_get which might take xtime lock for reading] 
> > 
> 
> Sounds right.  That's what was happening to me for a while.
> 
> Randy, it'd be interesting to try:
> 
> --- a/arch/x86_64/kernel/tsc.c~a
> +++ a/arch/x86_64/kernel/tsc.c
> @@ -84,8 +84,8 @@ static int time_cpufreq_notifier(struct 
>  		cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
>  
>  		tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
> -		if (!(freq->flags & CPUFREQ_CONST_LOOPS))
> -			mark_tsc_unstable("cpufreq changes");
> +//		if (!(freq->flags & CPUFREQ_CONST_LOOPS))
> +//			mark_tsc_unstable("cpufreq changes");
>  	}
>  
>  	return 0;
> _

I don't have CPU_FREQ enabled, so that didn't change anything.


> and if that "fixes" it, disable netconsole and do
> 
> --- a/arch/x86_64/kernel/tsc.c~a
> +++ a/arch/x86_64/kernel/tsc.c
> @@ -85,7 +85,7 @@ static int time_cpufreq_notifier(struct 
>  
>  		tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
>  		if (!(freq->flags & CPUFREQ_CONST_LOOPS))
> -			mark_tsc_unstable("cpufreq changes");
> +			dump_stack();
>  	}
>  
>  	return 0;


---
~Randy
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