Messages in this thread | | | Subject | Re: [PATH -mm -v2] Fix a race condtion of oops_in_progress | From | Huang Ying <> | Date | Tue, 11 Nov 2008 09:05:18 +0800 |
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On Mon, 2008-11-10 at 15:35 +0800, KOSAKI Motohiro wrote: > > > > As far as I know, barriers don't cause changes to be visible on other > > > > CPUs faster too. It just guarantees corresponding operations after will > > > > not get executed until that before have finished. And, I don't think we > > > > need make changes to be visible on other CPUs faster. > > > > > > You're correct that barrier() has no impact on other CPUs. wmb() and rmb() do. > > > If we don't need to make changes visible any faster, what's the point in using > > > atomic_set()? It's not any less racy. atomic_inc() and atomic_dec() would be > > > less racy, but you're not using those. > > > > In default bust_spinlocks() implementation in lib/bust_spinlocks.c, > > atomic_inc() and atomic_dec_and_test() is used. Which is used by x86 > > too. In some other architecture, atomic_set() is used to replace > > "oops_in_progress = <xxx>". So this patch fixes architectures which use > > default bust_spinlocks(), other architectures can be fixed by > > corresponding architecture developers. > > I think Chris is right. > So, I reccomend to read Documentation/memory-barriers.txt > > Almost architecture gurantee atomic_inc cause barrier implicitly. > but not _all_ architecture.
Yes. atomic_inc() doesn't imply barrier on all architecture. But we should not add barriers before all atomic_inc(), just ones needed. Can you figure out which ones in the patch should has barrier added?
Best Regards, Huang Ying
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