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
Date: Mon, 16 Sep 2019 11:22:18 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1909161119160.1489-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20190916051753.GA29216@tardis>
On Mon, 16 Sep 2019, Boqun Feng wrote:
> > executes if Y is a store.) This is expressed by the visibility
> > relation (vis), where X ->vis Y is defined to hold if there is an
> > intermediate event Z such that:
> >
> > X is connected to Z by a possibly empty sequence of
> > cumul-fence links followed by an optional rfe link (if none of
> > these links are present, X and Z are the same event),
> >
>
> I wonder whehter we could add an optional ->coe or ->fre between X and
> the possibly empty sequence of cumul-fence, smiliar to the definition
> of ->prop. This makes sense because if we have
>
> X ->coe X' (and X' in on CPU C)
>
> , X must be already propagated to C before X' executed, according to our
> operation model:
>
> "... In particular, it must arrange for the store to be co-later than
> (i.e., to overwrite) any other store to the same location which has
> already propagated to CPU C."
You have misinterpreted the text. The operational model says that if X
propagates to CPU C before X' executes then X ->coe X'. It does _not_
say that if X ->coe X' then X propagates to CPU C before X' executes.
> In other words, we can define ->vis as:
>
> let vis = prop ; ((strong-fence ; [Marked] ; xbstar) | (xbstar & int))
>
> , and for this document, reference the "prop" section in
> explanation.txt. This could make the model simple (both for description
> and explanation), and one better thing is that we won't need commit in
> Paul's dev branch:
>
> c683f2c807d2 "tools/memory-model: Fix data race detection for unordered store and load"
>
> , and data race rules will look more symmetrical ;-)
>
> Thoughts? Or am I missing something subtle here?
See above.
Alan
next prev parent reply other threads:[~2019-09-16 15:22 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-06 18:11 Documentation for plain accesses and data races Alan Stern
2019-09-12 22:01 ` Paul E. McKenney
2019-09-13 15:21 ` Alan Stern
2019-09-13 23:17 ` Paul E. McKenney
2019-09-13 19:13 ` Alan Stern
2019-09-15 23:13 ` Paul E. McKenney
2019-09-16 5:17 ` Boqun Feng
2019-09-16 11:52 ` Boqun Feng
2019-09-16 15:25 ` Alan Stern
2019-09-16 15:22 ` Alan Stern [this message]
2019-09-16 16:42 ` Boqun Feng
2019-09-27 8:59 ` Andrea Parri
2019-09-27 14:22 ` Alan Stern
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