linux-kernel - Re: [PATCH v3] tools/memory-model/Documentation: Fix "conflict" definition

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Date:   Mon, 2 Mar 2020 10:44:33 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Marco Elver <elver@...gle.com>, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, parri.andrea@...il.com,
        will@...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, dlustig@...dia.com,
        joel@...lfernandes.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH v3] tools/memory-model/Documentation: Fix "conflict"
 definition

On Mon, Mar 02, 2020 at 12:56:59PM -0500, Alan Stern wrote:
> On Mon, 2 Mar 2020, Marco Elver wrote:
> 
> > The definition of "conflict" should not include the type of access nor
> > whether the accesses are concurrent or not, which this patch addresses.
> > The definition of "data race" remains unchanged.
> > 
> > The definition of "conflict" as we know it and is cited by various
> > papers on memory consistency models appeared in [1]: "Two accesses to
> > the same variable conflict if at least one is a write; two operations
> > conflict if they execute conflicting accesses."
> > 
> > The LKMM as well as the C11 memory model are adaptations of
> > data-race-free, which are based on the work in [2]. Necessarily, we need
> > both conflicting data operations (plain) and synchronization operations
> > (marked). For example, C11's definition is based on [3], which defines a
> > "data race" as: "Two memory operations conflict if they access the same
> > memory location, and at least one of them is a store, atomic store, or
> > atomic read-modify-write operation. In a sequentially consistent
> > execution, two memory operations from different threads form a type 1
> > data race if they conflict, at least one of them is a data operation,
> > and they are adjacent in <T (i.e., they may be executed concurrently)."
> > 
> > [1] D. Shasha, M. Snir, "Efficient and Correct Execution of Parallel
> >     Programs that Share Memory", 1988.
> > 	URL: http://snir.cs.illinois.edu/listed/J21.pdf
> > 
> > [2] S. Adve, "Designing Memory Consistency Models for Shared-Memory
> >     Multiprocessors", 1993.
> > 	URL: http://sadve.cs.illinois.edu/Publications/thesis.pdf
> > 
> > [3] H.-J. Boehm, S. Adve, "Foundations of the C++ Concurrency Memory
> >     Model", 2008.
> > 	URL: https://www.hpl.hp.com/techreports/2008/HPL-2008-56.pdf
> > 
> > Signed-off-by: Marco Elver <elver@...gle.com>
> > Co-developed-by: Alan Stern <stern@...land.harvard.edu>
> > Signed-off-by: Alan Stern <stern@...land.harvard.edu>
> > ---
> > v3:
> > * Apply Alan's suggestion.
> > * s/two race candidates/race candidates/
> 
> Looks good!

Applied, thank you both!

							Thanx, Paul