Re: [patch 2] mm: speculative get_page

Nick Piggin
2005-06-28T23:43:31Z

Christoph Lameter wrote:
> On Wed, 29 Jun 2005, Nick Piggin wrote:
>
>
>>But nit picking aside, is it true that we need a load barrier before
>>unlock? (store barrier I agree with) The ppc64 changeset in question
>>indicates yes, but I can't quite work out why. There are noises in the
>>archives about this, but I didn't pinpoint a conclusion...
>
>
> A spinlock may be used to read a consistent set of variables. If load
> operations would be moved below the spin_unlock then one may get values
> that have been updated after another process acquired the spinlock.
>
>

Of course, thanks. I was only thinking of the case where loads
were moved from the unlocked into the locked section.

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