linux-kernel - Re: [PATCH] x86: use WRITE_ONCE/READ_ONCE in smp_store_release/smp_load

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Message-ID: <20150801165516.GB15407@nazgul.tnic>
Date:	Sat, 1 Aug 2015 18:55:16 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Andrey Konovalov <andreyknvl@...gle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	"David S. Miller" <davem@...emloft.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Alexander Duyck <alexander.h.duyck@...hat.com>,
	linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH] x86: use WRITE_ONCE/READ_ONCE in
 smp_store_release/smp_load_acquire

On Sat, Aug 01, 2015 at 06:45:34PM +0200, Andrey Konovalov wrote:
> Replace ACCESS_ONCE() macro in smp_store_release() and smp_load_acquire()
> from arch/x86/include/asm/barrier.h with WRITE_ONCE() and READ_ONCE() since
> ACCESS_ONCE does not work reliably on non-scalar types.
> 
> WRITE_ONCE() and READ_ONCE() were introduced in the commits 230fa253df63
> ("kernel: Provide READ_ONCE and ASSIGN_ONCE") and 43239cbe79fc ("kernel:
> Change ASSIGN_ONCE(val, x) to WRITE_ONCE(x, val)").

You actually forgot to CC the author. Let me add some more people to CC,
in addition.

> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  arch/x86/include/asm/barrier.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
> index e51a8f8..d2bcfbe 100644
> --- a/arch/x86/include/asm/barrier.h
> +++ b/arch/x86/include/asm/barrier.h
> @@ -57,12 +57,12 @@
>  do {									\
>  	compiletime_assert_atomic_type(*p);				\
>  	smp_mb();							\
> -	ACCESS_ONCE(*p) = (v);						\
> +	WRITE_ONCE(*p, v);						\
>  } while (0)
>  
>  #define smp_load_acquire(p)						\
>  ({									\
> -	typeof(*p) ___p1 = ACCESS_ONCE(*p);				\
> +	typeof(*p) ___p1 = READ_ONCE(*p);				\
>  	compiletime_assert_atomic_type(*p);				\
>  	smp_mb();							\
>  	___p1;								\
> @@ -74,12 +74,12 @@ do {									\
>  do {									\
>  	compiletime_assert_atomic_type(*p);				\
>  	barrier();							\
> -	ACCESS_ONCE(*p) = (v);						\
> +	WRITE_ONCE(*p, v);						\
>  } while (0)
>  
>  #define smp_load_acquire(p)						\
>  ({									\
> -	typeof(*p) ___p1 = ACCESS_ONCE(*p);				\
> +	typeof(*p) ___p1 = READ_ONCE(*p);				\
>  	compiletime_assert_atomic_type(*p);				\
>  	barrier();							\
>  	___p1;								\
> -- 
> 2.5.0.rc2.392.g76e840b
> 

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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