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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Fri, 10 Jan 2020 20:46:44 +0100
Message-ID: <CAK8P3a1UzSOHdihbzOn5CZZfo1kvCdj7BAzdQE=PgYS9GBF4Hw@mail.gmail.com>
Subject: Re: [RFC PATCH 0/8] Rework READ_ONCE() to improve codegen
To:     Will Deacon <will@kernel.org>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Segher Boessenkool <segher@kernel.crashing.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
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On Fri, Jan 10, 2020 at 5:56 PM Will Deacon <will@kernel.org> wrote:
>
> I have more patches in this area because I'm trying to move all the
> read_barrier_depends() magic into arch/alpha/, but I'm holding off until
> we agree on this part first.

Isn't the read_barrier_depends() the only reason for actually needing
the temporary local variable that must not be volatile?

If you make alpha provide its own READ_ONCE() as the first
step, it would seem that the rest of the series gets much easier
as the others can go back to the simple statement from your

#define __READ_ONCE(x)  (*(volatile __unqual_scalar_typeof(x) *)&(x))

      Arnd