linux-kernel - Re: [PATCH v3] tools/memory-model: Weaken ctrl dependency definition in explanation.txt

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Message-ID: <YxN4s+ZcPiV7u5XG@rowland.harvard.edu>
Date:   Sat, 3 Sep 2022 11:54:27 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Paul Heidekrüger <Paul.Heidekrueger@...tum.de>
Cc:     Andrea Parri <parri.andrea@...il.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Marco Elver <elver@...gle.com>,
        Charalampos Mainas <charalampos.mainas@...il.com>,
        Pramod Bhatotia <pramod.bhatotia@...tum.de>,
        Soham Chakraborty <s.s.chakraborty@...elft.nl>,
        Martin Fink <martin.fink@...tum.de>
Subject: Re: [PATCH v3] tools/memory-model: Weaken ctrl dependency definition
 in explanation.txt

On Sat, Sep 03, 2022 at 01:41:34PM +0200, Paul Heidekrüger wrote:
> On 3. Sep 2022, at 03:27, Alan Stern <stern@...land.harvard.edu> wrote:
> 
> > On Fri, Sep 02, 2022 at 09:13:40PM +0000, Paul Heidekrüger wrote:
> >> +Finally, a read event X and another memory access event Y are linked by
> >> +a control dependency if Y syntactically lies within an arm of an if
> >> +statement and X affects the evaluation of the if condition via a data or
> >> +address dependency (or similarly for a switch statement).  Simple
> >> +example:
> >> 
> >> 	int x, y;
> 
> Hang on, shouldn't this read "a write event" instead of "another memory
> access event"? Control dependencies only provide ordering from READ_ONCE to
> WRITE_ONCE, not from READ_ONCE to (READ | WRITE)_ONCE?
> 
> Or am I missing something?

Whoops, you're right.  Somehow I missed that.  Go ahead and change it; 
you can keep by S-O-B.

Alan