Messages in this thread | | | Date | Wed, 31 Oct 2001 11:40:02 -0700 | From | Andreas Dilger <> | Subject | Re: [Patch] Re: Nasty suprise with uptime |
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On Oct 31, 2001 19:16 +0100, Tim Schmielau wrote: > The idea was that all drivers that use the 32 bit jiffies counter have to > be aware of the wraparound anyways, and won't see a difference.
Agreed. I also like the change that you initialize jiffies to a pre-wrap value, so the jiffies wrap bugs can more easily be found/fixed.
> The race only happens for 64 bit accesses to jiffies, but hey, without > the patch these values come out wrong _every_ time, so I believed a > tiny window for a single wrong display of uptime every 497.1 days to be > acceptable.
I would say that the race is so rare that it should not be handled, especially since it adds extra code in the timer interrupt.
> + /* We need to make sure jiffies_high does not change while > + * reading jiffies and jiffies_high */ > + do { > + jiffies_high_tmp = jiffies_high_shadow; > + barrier(); > + jiffies_tmp = jiffies; > + barrier(); > + } while (jiffies_high != jiffies_high_tmp);
Maybe this could be condensed into a macro/inline, so that people don't screw it up (and it looks cleaner). Like get_jiffies64() or so, for those few places that really care about the full value and can't stand a miniscule chance of a race (i.e. uptime output is not a candidate).
Cheers, Andreas -- Andreas Dilger http://sourceforge.net/projects/ext2resize/ http://www-mddsp.enel.ucalgary.ca/People/adilger/
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