From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Lameter <clameter@sgi.com>
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
 architectures
Date: Fri, 24 Aug 2007 10:15:47 -0700 (PDT)
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Cc: Paul Mackerras <paulus@samba.org>,
	Satyam Sharma <satyam@infradead.org>,
	Stefan Richter <stefanr@s5r6.in-berlin.de>,
	Chris Snook <csnook@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arch@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	netdev@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
	ak@suse.de, heiko.carstens@de.ibm.com, davem@davemloft.net,
	schwidefsky@de.ibm.com, wensong@linux-vs.org, horms@verge.net.au,
	wjiang@resilience.com, cfriesen@nortel.com, zlynx@acm.org,
	rpjday@mindspring.com, jesper.juhl@gmail.com,
	segher@kernel.crashing.org,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Denys Vlasenko <vda.linux@googlemail.com>
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On Fri, 24 Aug 2007, Denys Vlasenko wrote:

> On Thursday 16 August 2007 00:22, Paul Mackerras wrote:
> > Satyam Sharma writes:
> > In the kernel we use atomic variables in precisely those situations
> > where a variable is potentially accessed concurrently by multiple
> > CPUs, and where each CPU needs to see updates done by other CPUs in a
> > timely fashion.  That is what they are for.  Therefore the compiler
> > must not cache values of atomic variables in registers; each
> > atomic_read must result in a load and each atomic_set must result in a
> > store.  Anything else will just lead to subtle bugs.
> 
> Amen.

A "timely" fashion? One cannot rely on something like that when coding. 
The visibility of updates is insured by barriers and not by some fuzzy 
notion of "timeliness".