linux-kernel - Re: [PATCH] make atomic_t volatile on all architectures

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Message-Id: <E1IJ424-0000d7-HK@be1.lrz>
Date:	Thu, 09 Aug 2007 11:10:16 +0200
From:	Bodo Eggert <7eggert@....de>
To:	Jerry Jiang <wjiang@...ilience.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Snook <csnook@...hat.com>, akpm@...ux-foundation.org,
	ak@...e.de, heiko.carstens@...ibm.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	schwidefsky@...ibm.com, wensong@...ux-vs.org, horms@...ge.net.au,
	cfriesen@...tel.com, zlynx@....org
Subject: Re: [PATCH] make atomic_t volatile on all architectures

Jerry Jiang <wjiang@...ilience.com> wrote:
> On Wed, 8 Aug 2007 21:18:25 -0700 (PDT)
>> On Wed, 8 Aug 2007, Chris Snook wrote:

>> > Some architectures currently do not declare the contents of an atomic_t to
>> > be
>> > volatile.  This causes confusion since atomic_read() might not actually
>> > read anything if an optimizing compiler re-uses a value stored in a
>> > register, which can break code that loops until something external changes
>> > the value of an atomic_t.
>> 
>> I'd be *much* happier with "atomic_read()" doing the "volatile" instead.
>> 
>> The fact is, volatile on data structures is a bug. It's a wart in the C
>> language. It shouldn't be used.
> 
> Why? It's a wart! Is it due to unclear C standard on volatile related point?
> 
> Why the *volatile-accesses-in-code* is acceptable, does C standard make it
> clear?

http://lwn.net/Articles/233482/
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