linux-kernel - Re: f68f031d ("Documentation: atomic_t.txt: Explain ordering provided by smp_mb__{before,after}

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Date:   Fri, 3 May 2019 12:19:21 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        <linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>
Subject: Re: f68f031d ("Documentation: atomic_t.txt: Explain ordering provided
 by smp_mb__{before,after}_atomic()")

On Fri, 3 May 2019, Peter Zijlstra wrote:

> On Fri, May 03, 2019 at 07:53:26AM -0700, Paul E. McKenney wrote:
> > Hello, Alan,
> > 
> > Just following up on the -rcu commit below.  I believe that it needs
> > some adjustment given Peter Zijlstra's addition of "memory" to the x86
> > non-value-returning atomics, but thought I should double-check.
> 
> Right; I should get back to that thread...

The real question, still outstanding, is whether smp_mb__before_atomic 
orders anything following the RMW instruction (and similarly, whether 
smp_mb__after_atomic orders anything preceding the RMW instruction).

The other changes in that patch (i.e., the second and third hunks) are 
okay in any case, because they just flesh out an explanation that is 
already present in the text.

Alan