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

From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will.deacon@arm.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Daniel Lustig <dlustig@nvidia.com>,
	David Howells <dhowells@redhat.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	Nicholas Piggin <npiggin@gmail.com>,
	Kernel development list <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire
Date: Thu, 12 Jul 2018 23:13:48 +0200	[thread overview]
Message-ID: <20180712211348.GA5308@andrea> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1807121637050.1306-100000@iolanthe.rowland.org>

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