On Fri, 2 Apr 2010, Linus Torvalds wrote:
quoted text
> 
> All that matters is that the above kind of while loop must work. The 
> architecture needs to do whatever it needs to do to make it work. End of 
> discussion. If on ARM6 that means "smp_mb()", then that's an ARM6 
> implementation issue.

Put another way: from a kernel standpoint, cpu_relax() in _no_ way implies 
a memory barrier. That has always been true, and that continues to be 
true.

But Linux does expect that if some other CPU modifies a memory location, 
then we _will_ see that modification eventually. If the CPU needs help to 
do so, then cpu_relax() needs to do that. Again - this has nothing to do 
with memory barriers. It's just a basic requirement.

				Linus
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