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.

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