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

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Message-ID: <20200506153639.GD5281@hirez.programming.kicks-ass.net>
Date:   Wed, 6 May 2020 17:36:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        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>
Subject: Re: [patch V4 part 1 06/36] compiler: Simple READ/WRITE_ONCE()
 implementations

On Wed, May 06, 2020 at 02:33:33PM +0100, Will Deacon wrote:
> 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@...radead.org>
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.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.

Ah excellent, clearly we had slightly different resoltions vs kcsan.
Thanks!