linux-kernel - Re: [PATCH 06/31] arch,arm: Convert smp_mb_

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Date:	Mon, 14 Apr 2014 17:19:06 +0100
From:	Will Deacon <will.deacon@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 06/31] arch,arm: Convert smp_mb__*

On Wed, Mar 19, 2014 at 06:47:35AM +0000, Peter Zijlstra wrote:
> ARM uses ll/sc primitives that do not imply barriers for all regular
> atomic ops, therefore smp_mb__{before,after} need be a full barrier.
> 
> Since ARM doesn't use asm-generic/barrier.h include the required
> definitions in its asm/barrier.h
> 
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>

  Acked-by: Will Deacon <will.deacon@....com>

Will

> ---
>  arch/arm/include/asm/atomic.h  |    5 -----
>  arch/arm/include/asm/barrier.h |    3 +++
>  arch/arm/include/asm/bitops.h  |    4 +---
>  3 files changed, 4 insertions(+), 8 deletions(-)
> 
> --- a/arch/arm/include/asm/atomic.h
> +++ b/arch/arm/include/asm/atomic.h
> @@ -211,11 +211,6 @@ static inline int __atomic_add_unless(at
>  
>  #define atomic_add_negative(i,v) (atomic_add_return(i, v) < 0)
>  
> -#define smp_mb__before_atomic_dec()	smp_mb()
> -#define smp_mb__after_atomic_dec()	smp_mb()
> -#define smp_mb__before_atomic_inc()	smp_mb()
> -#define smp_mb__after_atomic_inc()	smp_mb()
> -
>  #ifndef CONFIG_GENERIC_ATOMIC64
>  typedef struct {
>  	long long counter;
> --- a/arch/arm/include/asm/barrier.h
> +++ b/arch/arm/include/asm/barrier.h
> @@ -79,5 +79,8 @@ do {									\
>  
>  #define set_mb(var, value)	do { var = value; smp_mb(); } while (0)
>  
> +#define smp_mb__before_atomic()	smp_mb()
> +#define smp_mb__after_atomic()	smp_mb()
> +
>  #endif /* !__ASSEMBLY__ */
>  #endif /* __ASM_BARRIER_H */
> --- a/arch/arm/include/asm/bitops.h
> +++ b/arch/arm/include/asm/bitops.h
> @@ -25,9 +25,7 @@
>  
>  #include <linux/compiler.h>
>  #include <linux/irqflags.h>
> -
> -#define smp_mb__before_clear_bit()	smp_mb()
> -#define smp_mb__after_clear_bit()	smp_mb()
> +#include <asm/barrier.h>
>  
>  /*
>   * These functions are the basis of our bit ops.
> 
> 
> 
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