linux-kernel - Re: [PATCH RFC LKMM 1/7] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire

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Date:   Mon, 3 Sep 2018 20:28:05 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Will Deacon <will.deacon@....com>,
        Andrea Parri <parri.andrea@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, peterz@...radead.org, boqun.feng@...il.com,
        npiggin@...il.com, dhowells@...hat.com, j.alglave@....ac.uk,
        luc.maranget@...ia.fr, akiyks@...il.com
Subject: Re: [PATCH RFC LKMM 1/7] tools/memory-model: Add extra ordering for
 locks and remove it for ordinary release/acquire

On Mon, Sep 03, 2018 at 01:52:07PM -0400, Alan Stern wrote:
> On Mon, 3 Sep 2018, Andrea Parri wrote:
> 
> > In Cat speak,
> > 
> > diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat
> > index 59b5cbe6b6240..fd9c0831adf0a 100644
> > --- a/tools/memory-model/linux-kernel.cat
> > +++ b/tools/memory-model/linux-kernel.cat
> > @@ -38,7 +38,7 @@ let strong-fence = mb | gp
> >  (* Release Acquire *)
> >  let acq-po = [Acquire] ; po ; [M]
> >  let po-rel = [M] ; po ; [Release]
> > -let rfi-rel-acq = [Release] ; rfi ; [Acquire]
> > +let po-rel-rf-acq-po = po ; [Release] ; rf ; [Acquire] ; po
> >  
> >  (**********************************)
> >  (* Fundamental coherence ordering *)
> > @@ -60,13 +60,13 @@ let dep = addr | data
> >  let rwdep = (dep | ctrl) ; [W]
> >  let overwrite = co | fr
> >  let to-w = rwdep | (overwrite & int)
> > -let to-r = addr | (dep ; rfi) | rfi-rel-acq
> > +let to-r = addr | (dep ; rfi)
> >  let fence = strong-fence | wmb | po-rel | rmb | acq-po
> > -let ppo = to-r | to-w | fence
> > +let ppo = to-r | to-w | fence | (po-rel-rf-acq-po & int)
> >  
> >  (* Propagation: Ordering from release operations and strong fences. *)
> >  let A-cumul(r) = rfe? ; r
> > -let cumul-fence = A-cumul(strong-fence | po-rel) | wmb
> > +let cumul-fence = A-cumul(strong-fence | po-rel) | wmb | po-rel-rf-acq-po
> >  let prop = (overwrite & ext)? ; cumul-fence* ; rfe?
> >  
> >  (*
> 
> I thought the goal you were aiming for was a patch making
> atomic-acquire/ordinary-release be RCtso (along with lock/unlock),
> while leaving ordinary-acquire/ordinary-release to remain RCpc.  

Such a patch would belong to the second approach (the "two distinct
release-acquire" approach from my previous email).


> Clearly that is not what this patch does.

I meant the above ;-)  to illustrate yet another approach (not that
it makes me happy, as should be clear from previous posts ;-).

  Andrea


> 
> Alan
>