linux-kernel - Re: [PATCH] tools/memory-model: Document herd7 (internal) representation

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Date: Mon, 27 May 2024 09:37:40 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Andrea Parri <parri.andrea@...il.com>
Cc: Hernan Ponce de Leon <hernan.poncedeleon@...weicloud.com>,
  will@...nel.org, peterz@...radead.org, boqun.feng@...il.com,
  npiggin@...il.com, dhowells@...hat.com, j.alglave@....ac.uk,
  luc.maranget@...ia.fr, paulmck@...nel.org, akiyks@...il.com,
  dlustig@...dia.com, joel@...lfernandes.org, linux-kernel@...r.kernel.org,
  linux-arch@...r.kernel.org, jonas.oberhauser@...weicloud.com
Subject: Re: [PATCH] tools/memory-model: Document herd7 (internal)
 representation

On Mon, May 27, 2024 at 03:28:00PM +0200, Andrea Parri wrote:
> > > +    |                smp_store_mb | W[once] ->po F[mb]                        |
> > 
> > I expect this one to be hard-coded in herd7 source code, but I cannot find
> > it. Can you give me a pointer?
> 
> smp_store_mb() is currently mapped to { __store{once}(X,V); __fence{mb}; } in
> the .def file, so it's semantically equivalent to "WRITE_ONCE(); smp_mb();".

Why don't we use this approach for all the value-returning full-barrier 
RMW operations?  That would immediately solve the issue of the 
special-purpose code in herd7, leaving only the matter of how to 
annotate failed RMW operations.

Alan