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Date: Fri, 17 Aug 2007 17:26:12 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
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To: Satyam Sharma <satyam@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Paul Mackerras <paulus@samba.org>, Segher Boessenkool <segher@kernel.crashing.org>, heiko.carstens@de.ibm.com, horms@verge.net.au, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, rpjday@mindspring.com, ak@suse.de, netdev@vger.kernel.org, cfriesen@nortel.com, Andrew Morton <akpm@linux-foundation.org>, jesper.juhl@gmail.com, linux-arch@vger.kernel.org, zlynx@acm.org, clameter@sgi.com, schwidefsky@de.ibm.com, Chris Snook <csnook@redhat.com>, Herbert Xu <herbert.xu@redhat.com>, davem@davemloft.net, wensong@linux-vs.org, wjiang@resilience.com
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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.