linux-kernel - Re: [PATCH 08/34] asm-generic: smp_store_mb should use smp

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Message-ID: <5946017.BCmPrpGMuh@wuerfel>
Date:	Wed, 30 Dec 2015 14:44:21 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	linux-arch@...r.kernel.org,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	virtualization@...ts.linux-foundation.org,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
Subject: Re: [PATCH 08/34] asm-generic: smp_store_mb should use smp_mb

On Wednesday 30 December 2015 15:24:47 Michael S. Tsirkin wrote:
> asm-generic variant of smp_store_mb() calls mb() which is stronger
> than implied by both the name and the documentation.
> 
> smp_store_mb is only used by core kernel code at the moment, so
> we know no one mis-uses it for an MMIO barrier.
> Make it call smp_mb consistently before some arch-specific
> code uses it as such by mistake.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  include/asm-generic/barrier.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
> index 538f8d1..987b2e0 100644
> --- a/include/asm-generic/barrier.h
> +++ b/include/asm-generic/barrier.h
> @@ -93,7 +93,7 @@
>  #endif	/* CONFIG_SMP */
>  
>  #ifndef smp_store_mb
> -#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); mb(); } while (0)
> +#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); smp_mb(); } while (0)
>  #endif
>  
>  #ifndef smp_mb__before_atomic
> 

The same patch is already in the tip tree scheduled for 4.5 as d5a73cadf3fd
("lcoking/barriers, arch: Use smp barriers in smp_store_release()").

I think you can drop your version.

	arnd

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