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Date:   Wed, 6 May 2020 14:33:33 +0100
From:   Will Deacon <will@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>
Subject: Re: [patch V4 part 1 06/36] compiler: Simple READ/WRITE_ONCE()
 implementations
Message-ID: <20200506133333.GK8043@willie-the-truck>
References: <20200505131602.633487962@linutronix.de>
 <20200505134058.651504242@linutronix.de>
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On Tue, May 05, 2020 at 03:16:08PM +0200, Thomas Gleixner wrote:
> READ/WRITE_ONCE_NOCHECK() is required for atomics in code which cannot be
> instrumented like the x86 int3 text poke code. As READ/WRITE_ONCE() is
> undergoing a rewrite, provide __{READ,WRITE}_ONCE_SCALAR().
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  include/linux/compiler.h |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -313,6 +313,14 @@ unsigned long read_word_at_a_time(const
>  	__u.__val;					\
>  })
>  
> +#define __READ_ONCE_SCALAR(x)				\
> +	(*(const volatile typeof(x) *)&(x))
> +
> +#define __WRITE_ONCE_SCALAR(x, val)			\
> +do {							\
> +	*(volatile typeof(x) *)&(x) = val;		\
> +} while (0)

FWIW, these end up being called __READ_ONCE() and __WRITE_ONCE() after
the rewrite; the *_SCALAR() variants will call into kcsan_check_atomic_*().

If you go with that naming now, then any later conflict should fall out in
the wash.

Will