linux-kernel - Re: [PATCH] Linux: Implement membarrier function

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Date:   Wed, 12 Dec 2018 13:04:44 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
cc:     David Goldblatt <davidtgoldblatt@...il.com>,
        <mathieu.desnoyers@...icios.com>,
        Florian Weimer <fweimer@...hat.com>, <triegel@...hat.com>,
        <libc-alpha@...rceware.org>, <andrea.parri@...rulasolutions.com>,
        <will.deacon@....com>, <peterz@...radead.org>,
        <boqun.feng@...il.com>, <npiggin@...il.com>, <dhowells@...hat.com>,
        <j.alglave@....ac.uk>, <luc.maranget@...ia.fr>, <akiyks@...il.com>,
        <dlustig@...dia.com>, <linux-arch@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Linux: Implement membarrier function

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