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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 17 Jul 2018 13:13:51 -0700
Message-ID: <CA+55aFyLp7DMp4jgJjV_Dj_KvMD--umZkqCDKBPbzH+sOZu24g@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:     Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Peter Zijlstra <peterz@infradead.org>,
        andrea.parri@amarulasolutions.com,
        Will Deacon <will.deacon@arm.com>,
        Akira Yokosawa <akiyks@gmail.com>,
        Boqun Feng <boqun.feng@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>,
        Nick Piggin <npiggin@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, Jul 17, 2018 at 12:37 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> Why not?  Instructions are allowed to migrate _into_ critical sections,
> just not _out_ of them.  So a store preceding the start of a spinlocked
> region can migrate in and be executed after a load that is inside the
> region.

Hmm, yes of course. But the isync instruction description I found also
talks about the previous instructions being "completed".

But yeah, that obviously can mean just "in the store buffer", not
actually ordered.

           Linus