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From: Christoph Lameter <clameter@sgi.com>
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
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On Mon, 10 Sep 2007, Paul E. McKenney wrote:

> The one exception to this being the case where process-level code is
> communicating to an interrupt handler running on that same CPU -- on
> all CPUs that I am aware of, a given CPU always sees its own writes
> in order.

Yes but that is due to the code path effectively continuing in the 
interrupt handler. The cpu makes sure that op codes being executed always 
see memory in a consistent way. The basic ordering problem with out of 
order writes is therefore coming from other processors concurrently 
executing code and holding variables in registers that are modified 
elsewhere. The only solution that I know of are one or the other form of 
barrier.