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Date:   Mon, 16 Sep 2019 11:25:07 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Boqun Feng <boqun.feng@gmail.com>
cc:     LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
        Andrea Parri <parri.andrea@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>,
        "Paul E. McKenney" <paulmck@linux.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Will Deacon <will@kernel.org>,
        Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: Documentation for plain accesses and data races
In-Reply-To: <20190916115254.GB29216@tardis>
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On Mon, 16 Sep 2019, Boqun Feng wrote:

> > In other words, we can define ->vis as:
> > 
> > 	let vis = prop ; ((strong-fence ; [Marked] ; xbstar) | (xbstar & int))
> > 
> 
> Hmm.. so the problem with this approach is that the (xbstar & int) part
> doesn't satisfy the requirement of visibility... i.e.
> 
> 	X ->prop Z ->(xbstar & int) Y
> 
> may not guarantee when Y executes, X is already propagated to Y's CPU.

Yes, it doesn't guarantee this.  But the reason it doesn't guarantee 
this is because of the prop.  The (xbstar & int) part is okay.  In 
other words, if

	Z ->(xbstar & int) Y

then it is certainly true that any store propagating to Z's CPU before 
Z executes also propagates to Y's CPU (which is the same one) before Y 
executes.

Alan