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

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Message-Id: <1f265c14b28f2c5922059a130b1d8aa5@kernel.crashing.org>
Date:	Sat, 18 Aug 2007 00:14:30 +0200
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	paulmck@...ux.vnet.ibm.com, Christoph Lameter <clameter@....com>,
	Paul Mackerras <paulus@...ba.org>, heiko.carstens@...ibm.com,
	Stefan Richter <stefanr@...6.in-berlin.de>, horms@...ge.net.au,
	Satyam Sharma <satyam@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	rpjday@...dspring.com, netdev@...r.kernel.org, ak@...e.de,
	cfriesen@...tel.com, jesper.juhl@...il.com,
	linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, zlynx@....org,
	schwidefsky@...ibm.com, Chris Snook <csnook@...hat.com>,
	Herbert Xu <herbert@...dor.apana.org.au>, davem@...emloft.net,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	wensong@...ux-vs.org, wjiang@...ilience.com
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

> (and yes, it is perfectly legitimate to
> want a non-volatile read for a data type that you also want to do
> atomic RMW operations on)

...which is undefined behaviour in C (and GCC) when that data is
declared volatile, which is a good argument against implementing
atomics that way in itself.


Segher

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