linux-kernel - Re: [PATCH] memory-model: fix cheat sheet typo

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Message-ID: <20180411163157.GQ4082@hirez.programming.kicks-ass.net>
Date:   Wed, 11 Apr 2018 18:31:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Will Deacon <will.deacon@....com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Akira Yokosawa <akiyks@...il.com>
Subject: Re: [PATCH] memory-model: fix cheat sheet typo

On Wed, Apr 11, 2018 at 09:19:56AM -0700, Paul E. McKenney wrote:

> > 
> >                                    Prior Operation   Subsequent Operation
> >                                    ---------------   ---------------------
> >                                    R  W  RMW  SV     R  W  DR  DW  RMW  SV
> >                                    -  -  ---  --     -  -  --  --  ---  --

> > smp_store_mb()                     Y  Y    Y   Y      Y  Y   Y   Y   Y   Y

I'm not sure about that, the generic version of that reads:

include/asm-generic/barrier.h:#define __smp_store_mb(var, value)  do { WRITE_ONCE(var, value); __smp_mb(); } while (0)

Which doesn't not have an smp_mb() before, so it doesn't actually order
prior; or I'm failing to read the table wrong.