linux-kernel - Re: [PATCH 5/9] mips/gup: Replace ACCESS_ONCE with READ

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Message-ID: <20141204001116.GB25340@linux.vnet.ibm.com>
Date:	Wed, 3 Dec 2014 16:11:16 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH 5/9] mips/gup: Replace ACCESS_ONCE with READ_ONCE

On Wed, Dec 03, 2014 at 11:30:17PM +0100, Christian Borntraeger wrote:
> ACCESS_ONCE does not work reliably on non-scalar types. For
> example gcc 4.6 and 4.7 might remove the volatile tag for such
> accesses during the SRA (scalar replacement of aggregates) step
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)
> 
> Change the gup code to replace ACCESS_ONCE with READ_ONCE.
> 
> Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>

Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> ---
>  arch/mips/mm/gup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/mm/gup.c b/arch/mips/mm/gup.c
> index 06ce17c..8aa50e3 100644
> --- a/arch/mips/mm/gup.c
> +++ b/arch/mips/mm/gup.c
> @@ -30,7 +30,7 @@ retry:
> 
>  	return pte;
>  #else
> -	return ACCESS_ONCE(*ptep);
> +	return READ_ONCE(*ptep);
>  #endif
>  }
> 
> -- 
> 1.9.3
> 

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