linux-kernel - Re: [patch V4 part 1 06/36] compiler: Simple READ/WRITE

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Date:   Wed, 6 May 2020 15:11:21 +0200
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V4 part 1 06/36] compiler: Simple READ/WRITE_ONCE()
 implementations



On 5/5/20 3:16 PM, 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@...radead.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>   include/linux/compiler.h |    8 ++++++++
>   1 file changed, 8 insertions(+)

Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.com>

alex.

> --- 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)
> +
>   /**
>    * data_race - mark an expression as containing intentional data races
>    *
>