[RFC 2/2] rcu: Remove ->dynticks_nmi_nesting from struct rcu_dynticks

[Byungchul Park]

Hello folks,

I'm careful in saying that ->dynticks_nmi_nesting can be removed but I
think it's possible since the only thing we are interested in with
regard to ->dynticks_nesting or ->dynticks_nmi_nesting is whether rcu is
idle or not.

And I'm also afraid if the assumption is correct for every archs which I
based on, that is, an assignment operation on a single aligned word is
atomic in terms of instruction.

Thoughs?

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