linux-kernel - Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

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Message-ID: <46C5EDF9.3090507@nortel.com>
Date:	Fri, 17 Aug 2007 12:50:33 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Nick Piggin <piggin@...erone.com.au>,
	Satyam Sharma <satyam@...radead.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Paul Mackerras <paulus@...ba.org>,
	Christoph Lameter <clameter@....com>,
	Chris Snook <csnook@...hat.com>,
	Ilpo Jarvinen <ilpo.jarvinen@...sinki.fi>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, ak@...e.de,
	heiko.carstens@...ibm.com, David Miller <davem@...emloft.net>,
	schwidefsky@...ibm.com, wensong@...ux-vs.org, horms@...ge.net.au,
	wjiang@...ilience.com, zlynx@....org, rpjday@...dspring.com,
	jesper.juhl@...il.com, segher@...nel.crashing.org
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
 architectures

Linus Torvalds wrote:

>  - in other words, the *only* possible meaning for "volatile" is a purely 
>    single-CPU meaning. And if you only have a single CPU involved in the 
>    process, the "volatile" is by definition pointless (because even 
>    without a volatile, the compiler is required to make the C code appear 
>    consistent as far as a single CPU is concerned).

I assume you mean "except for IO-related code and 'random' values like 
jiffies" as you mention later on?  I assume other values set in 
interrupt handlers would count as "random" from a volatility perspective?

> So anybody who argues for "volatile" fixing bugs is fundamentally 
> incorrect. It does NO SUCH THING. By arguing that, such people only show 
> that you have no idea what they are talking about.

What about reading values modified in interrupt handlers, as in your 
"random" case?  Or is this a bug where the user of atomic_read() is 
invalidly expecting a read each time it is called?

Chris
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