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

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Date:   Fri, 13 Jul 2018 19:58:25 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     andrea.parri@...rulasolutions.com,
        Will Deacon <will.deacon@....com>,
        Daniel Lustig <dlustig@...dia.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Akira Yokosawa <akiyks@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Nick Piggin <npiggin@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and
 remove it for ordinary release/acquire

On Fri, Jul 13, 2018 at 6:51 PM Alan Stern <stern@...land.harvard.edu> wrote:
>
> The point being that the scenarios under discussion in this thread all
> fall most definitely into the "Non-standard usage; you'd better know
> exactly what you're doing" category.

Well, yes and no.

The thing is, people expected unlock+lock to give a memory ordering.
It happened in RCU, and it's happened before elsewhere.

So it *is* the "pure locking" thing that ends up confusing people.
Yes, you have some other access that then cares about the memory
ordering, but this is a fairly natural expectation to have
(considering that we've had the same issue before).

              Linus