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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 10 Jan 2020 12:14:45 -0800
Message-ID: <CAHk-=wggv_LmrL85Ez0TLcAku8iz05VZmJxDGo=2aP2VvQtrsA@mail.gmail.com>
Subject: Re: [RFC PATCH 0/8] Rework READ_ONCE() to improve codegen
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Will Deacon <will@kernel.org>,
        "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>,
        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 11:47 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> 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

Hmm.. The union still would cause that "take the address of a volatile
thing on the stack" problem, wouldn't it? And that was what caused
most of the issues.

I think the _real_ issue is how KASAN forces that odd pair of inline
functions in order to have the annotations on the accesses.

                Linus