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

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Message-ID: <Pine.LNX.4.44L0.1905031252060.1437-100000@iolanthe.rowland.org>
Date:   Fri, 3 May 2019 12:52:39 -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 12:19:21PM -0400, Alan Stern wrote:
> > 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).
> 
> Yes -- that was very much the intent, and only (some) x86 ops and (some)
> MIPS config have issues with that.

Okay, then I better update the patch.

Alan