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From: "Petr Vandrovec" <VANDROVE@vc.cvut.cz>
Organization: CC CTU Prague
To: Tim Schmielau <tim@physik3.uni-rostock.de>
Date: Thu, 1 Nov 2001 09:02:44 MET-1
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Subject: Re: [Patch] Re: Nasty suprise with uptime
CC: <linux-kernel@vger.kernel.org>, J Sloan <jjs@lexus.com>,
        adilger@turbolabs.com
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On  1 Nov 01 at 1:52, Tim Schmielau wrote:

> +   static unsigned long jiffies_hi = 0;
> +   static unsigned long jiffies_last = INITIAL_JIFFIES;
> +   unsigned long jiffies_tmp;
> +
> +   jiffies_tmp = jiffies;   /* avoid races */
> +   if (jiffies_tmp < jiffies_last)   /* We have a wrap */
> +       jiffies_hi++;
> +   jiffies_last = jiffies_tmp;

There is very small race - if two processes will call get_jiffies64()
at same time, they can both happen to test jiffies_tmp < jiffies_last
with old jiffies_last - incrementing jiffies_hi twice :-( This race
window is only few microseconds every 497 days, but if we want
correct kernel... 
                                            Best regards,
                                                Petr Vandrovec
                                                vandrove@vc.cvut.cz
                                                
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