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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 13 Jul 2018 19:58:25 -0700
Message-ID: <CA+55aFwKpkU5C23OYt1HCiD3X5bJHVh1jz5G2dSnF1+kVrOCTA@mail.gmail.com>
Subject: Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and
 remove it for ordinary release/acquire
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     andrea.parri@amarulasolutions.com,
        Will Deacon <will.deacon@arm.com>,
        Daniel Lustig <dlustig@nvidia.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Akira Yokosawa <akiyks@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        David Howells <dhowells@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        Nick Piggin <npiggin@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Jul 13, 2018 at 6:51 PM Alan Stern <stern@rowland.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