Re: [PATCH 3/4] x86,asm: Re-work smp_store_mb()

From: Linus Torvalds
Date: Tue Oct 27 2015 - 17:34:06 EST

On Wed, Oct 28, 2015 at 4:53 AM, Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote:
> Note that this might affect callers that could/would rely on the
> atomicity semantics, but there are no guarantees of that for
> smp_store_mb() mentioned anywhere, plus most archs use this anyway.
> Thus we continue to be consistent with the memory-barriers.txt file,
> and more importantly, maintain the semantics of the smp_ nature.

So I dislike this patch, mostly because it now makes it obvious that
smp_store_mb() seems to be totally pointless. Every single
implementation is now apparently WRITE_ONCE+smp_mb(), and there are
what, five users of it, so why not then open-code it?

But more importantly, is the "WRITE_ONCE()" even necessary? If there
are no atomicity guarantees, then why bother with WRTE_ONCE() either?

So with this patch, the whole thing becomes pointless, I feel. (Ok, so
it may have been pointless before too, but at least before this patch
it generated special code, now it doesn't). So why carry it along at

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