Re: [RFC PATCH 1/4] asm-generic: cmpxchg: implement dummycmpxchg64_relaxed operation

[Linus Torvalds]

On Thu, Sep 26, 2013 at 8:13 AM, Will Deacon <will.deacon@xxxxxxx> wrote:
>
> This patch implements a dummy implementation for asm-generic, falling
> back to the usual cmpxchg64 code.

I don't like the "let's add dummy operations for everybody who doesn't
care" when it is this specialized.

I'd much rather just add a single

   #ifndef cmpxchg64_relaxed
   # define cmpxchg64_relaxed cmpxchg64
   #endif

to the LOCKREF code, and then ARM (and others) can define it as they wish.

And *if* anybody else ever realizes that they want this outside of the
lockref code, let's look at doing that then. Right now I don't know of
any users, and I'd be leery of people using this willy-nilly, because
very few people really understand memory ordering.

               Linus
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