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

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Message-ID: <CA+55aFyLp7DMp4jgJjV_Dj_KvMD--umZkqCDKBPbzH+sOZu24g@mail.gmail.com>
Date:   Tue, 17 Jul 2018 13:13:51 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Peter Zijlstra <peterz@...radead.org>,
        andrea.parri@...rulasolutions.com,
        Will Deacon <will.deacon@....com>,
        Akira Yokosawa <akiyks@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Lustig <dlustig@...dia.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 Tue, Jul 17, 2018 at 12:37 PM Alan Stern <stern@...land.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