linux-kernel - Re: [PATCH v2 RFC 1/3] documentation: Add needed ACCESS

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Message-ID: <20131122153908.GQ10022@twins.programming.kicks-ass.net>
Date:	Fri, 22 Nov 2013 16:39:08 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	darren@...art.com, fweisbec@...il.com, sbw@....edu
Subject: Re: [PATCH v2 RFC 1/3] documentation: Add needed ACCESS_ONCE() calls
 to memory-barriers.txt

On Thu, Nov 21, 2013 at 01:31:27PM -0800, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> 
> The Documentation/memory-barriers.txt file was written before the need
> for ACCESS_ONCE() was fully appreciated.  It therefore contains no
> ACCESS_ONCE() calls, which can be a problem when people lift examples
> from it.  This commit therefore adds ACCESS_ONCE() calls.
> 

Under the 'COMPILER BARRIER' section we state that:

"This is a general barrier - lesser varieties of compiler barrier do not
exist."

One could argue ACCESS_ONCE() is such a lesser barrier.
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