linux-kernel - Re: 2.6.32.21 - uptime related crashes?

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Message-ID: <20110721125008.GF11246@pcnci.linuxbox.cz>
Date:	Thu, 21 Jul 2011 14:50:08 +0200
From:	Nikola Ciprich <nikola.ciprich@...uxbox.cz>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, john stultz <johnstul@...ibm.com>,
	Willy Tarreau <w@....eu>,
	MINOURA Makoto <minoura@...inux.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Faidon Liambotis <paravoid@...ian.org>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	seto.hidetoshi@...fujitsu.com,
	Hervé Commowick <hcommowick@...sec.fr>,
	Rand@...per.es, Nikola Ciprich <nikola.ciprich@...uxbox.cz>
Subject: Re: 2.6.32.21 - uptime related crashes?

Hi,
thanks for the patch! I'll put this on our testing boxes...
Are You going to push this upstream so we can ask Greg to push this to -stable?
or do You plan to wait for more complex patch?
n.


On Thu, Jul 21, 2011 at 02:24:58PM +0200, Peter Zijlstra wrote:
> On Thu, 2011-07-21 at 09:22 +0200, Ingo Molnar wrote:
> > 
> > Ping, what's going on with this bug? Systems are crashing so we need 
> > a quick fix ASAP ... 
> 
> Something as simple as the below ought to cure things for now. Once we
> get __cycles_2_ns() fixed up we can enable it again.
> 
> (patch against -tip, .32 code is different but equally simple to fix)
> 
> ---
> Subject: x86, intel: Don't mark sched_clock() as stable
> 
> Because the x86 sched_clock() implementation wraps at 54 bits and the
> scheduler code assumes it wraps at the full 64bits we can get into
> trouble after 208 days (~7 months) of uptime. 
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  arch/x86/kernel/cpu/intel.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index ed6086e..c8dc48b 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -91,8 +91,15 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
>  	if (c->x86_power & (1 << 8)) {
>  		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
>  		set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
> +		/*
> +		 * Unfortunately our __cycles_2_ns() implementation makes
> +		 * the raw sched_clock() interface wrap at 54-bits, which
> +		 * makes it unsuitable for direct use, so disable this
> +		 * for now.
> +		 *
>  		if (!check_tsc_unstable())
>  			sched_clock_stable = 1;
> +		 */
>  	}
>  
>  	/*
> 
> 

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