linux-kernel - Re: [PATCH 01/13] compiler.h: Split {READ,WRITE}

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Message-ID: <CAK8P3a0f=WvSQSBQ4t0FmEkcFE_mC3oARxaeTviTSkSa-D2qhg@mail.gmail.com>
Date:   Fri, 8 Nov 2019 20:57:14 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Will Deacon <will@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Yunjae Lee <lyj7694@...il.com>,
        SeongJae Park <sj38.park@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Matt Turner <mattst88@...il.com>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Richard Henderson <rth@...ddle.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Joe Perches <joe@...ches.com>,
        Boqun Feng <boqun.feng@...il.com>,
        alpha <linux-alpha@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [PATCH 01/13] compiler.h: Split {READ,WRITE}_ONCE definitions out
 into rwonce.h

On Fri, Nov 8, 2019 at 6:01 PM Will Deacon <will@...nel.org> wrote:
>
> In preparation for allowing architectures to define their own
> implementation of the 'READ_ONCE()' macro, move the generic
> '{READ,WRITE}_ONCE()' definitions out of the unwieldy 'linux/compiler.h'
> and into a new 'rwonce.h' header under 'asm-generic'.

Adding Christian Bornträger to Cc, he originally added the
READ_ONCE()/WRITE_ONCE()
code.

I wonder if it would be appropriate now to revert back to a much simpler version
of these helpers for any modern compiler. As I understand, only gcc-4.6 and
gcc4.7 actually need the song-and-dance version with the union and switch/case,
while for others, we can might be able back to a macro doing a volatile access.

     Arnd