linux-kernel - Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire

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Date:   Thu, 12 Jul 2018 23:13:48 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        LKMM Maintainers -- Akira Yokosawa <akiyks@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Nicholas Piggin <npiggin@...il.com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and
 remove it for ordinary release/acquire

On Thu, Jul 12, 2018 at 04:43:46PM -0400, Alan Stern wrote:
> On Thu, 12 Jul 2018, Andrea Parri wrote:
> 
> > > It seems reasonable to ask people to learn that locks have stronger
> > > ordering guarantees than RMW atomics do.  Maybe not the greatest
> > > situation in the world, but one I think we could live with.
> > 
> > Yeah, this was one of my main objections.
> 
> Does this mean you don't think you could live with it?

Well, I *could* leave with it and with RCtso locks, ;-) but I'd rather not.

Assuming that I will not be able to resist this RCtso trend, ;-) would the
below (completely untested) work?

  let rmw = rmw | lk-rmw   (* from lock.cat *)
  let po-unlock-rf-lock-po = po ; [Release] ; rf ; [domain(rmw)] ; po
  [the rest of your patch + the updates to the doc. I suggested in v2 ;-)]

   Andrea