[PATCH 13/18] arm64: cmpxchg: avoid memory barrier on comparison failure

[Peter Zijlstra]

On Mon, Jul 13, 2015 at 10:25:14AM +0100, Will Deacon wrote:
> cmpxchg doesn't require memory barrier semantics when the value
> comparison fails, so make the barrier conditional on success.

So this isn't actually a documented condition.

I would very much like a fwe extra words on this, that you've indeed
audited cmpxchg() users and preferably even a Documentation/ update to
match.