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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Message-ID: <Pine.LNX.4.44L0.1809031346300.1940-100000@netrider.rowland.org>
Date:   Mon, 3 Sep 2018 13:52:07 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
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, 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.  
Clearly that is not what this patch does.

Alan