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

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Date:	Fri, 17 Aug 2007 17:26:12 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Satyam Sharma <satyam@...radead.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul Mackerras <paulus@...ba.org>,
	Segher Boessenkool <segher@...nel.crashing.org>,
	heiko.carstens@...ibm.com, horms@...ge.net.au,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	rpjday@...dspring.com, ak@...e.de, netdev@...r.kernel.org,
	cfriesen@...tel.com, Andrew Morton <akpm@...ux-foundation.org>,
	jesper.juhl@...il.com, linux-arch@...r.kernel.org, zlynx@....org,
	clameter@....com, schwidefsky@...ibm.com,
	Chris Snook <csnook@...hat.com>,
	Herbert Xu <herbert.xu@...hat.com>, davem@...emloft.net,
	wensong@...ux-vs.org, wjiang@...ilience.com
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
 architectures

Satyam Sharma wrote:

> #define atomic_read_volatile(v)				\
> 	({						\
> 		forget((v)->counter);			\
> 		((v)->counter);				\
> 	})
> 
> where:

*vomit* :)

Not only do I hate the keyword volatile, but the barrier is only a
one-sided affair so its probable this is going to have slightly
different allowed reorderings than a real volatile access.

Also, why would you want to make these insane accessors for atomic_t
types? Just make sure everybody knows the basics of barriers, and they
can apply that knowledge to atomic_t and all other lockless memory
accesses as well.


> #define forget(a)	__asm__ __volatile__ ("" :"=m" (a) :"m" (a))

I like order(x) better, but it's not the most perfect name either.

-- 
SUSE Labs, Novell Inc.
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