Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 12 Dec 2018 13:04:44 -0500 (EST)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     "Paul E. McKenney" <paulmck@linux.ibm.com>
cc:     David Goldblatt <davidtgoldblatt@gmail.com>,
        <mathieu.desnoyers@efficios.com>,
        Florian Weimer <fweimer@redhat.com>, <triegel@redhat.com>,
        <libc-alpha@sourceware.org>, <andrea.parri@amarulasolutions.com>,
        <will.deacon@arm.com>, <peterz@infradead.org>,
        <boqun.feng@gmail.com>, <npiggin@gmail.com>, <dhowells@redhat.com>,
        <j.alglave@ucl.ac.uk>, <luc.maranget@inria.fr>, <akiyks@gmail.com>,
        <dlustig@nvidia.com>, <linux-arch@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Linux: Implement membarrier function
In-Reply-To: <20181212170706.GA17397@linux.ibm.com>
Message-ID: <Pine.LNX.4.44L0.1812121302270.1543-100000@iolanthe.rowland.org>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, 12 Dec 2018, Paul E. McKenney wrote:

> > > > Or am I still missing something here?
> > > 
> > > You tell me...
> > 
> > I think I am on board.  ;-)
> 
> And more to the point, here is a three-process variant showing a cycle
> that is permitted:
> 
> 
>          P0      P1      P2
>          Wa=2    Wb=2    Wc=2
>          mb0s
>                  [mb01]  [mb02]
>          mb0e
>          Rb=0    Rc=0    Ra=0
> 
> As can be seen by reordering it as follows:
> 
>          P0      P1      P2
>                          Ra=0
>          Wa=2
>          mb0s
>                  [mb01]
>                  Rc=0
>                          Wc=2
>                          [mb02]
>          mb0e
>          Rb=0
>                  Wb=2
> 
> Make sense?

You got it!

Alan