linux-kernel - Re: [PATCH 24/24] document volatile atomic

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Message-Id: <8f6bb8a9e4f2819a161d732bdb6c70c0@kernel.crashing.org>
Date:	Thu, 9 Aug 2007 17:59:29 +0200
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Chris Snook <csnook@...hat.com>
Cc:	wjiang@...ilience.com, wensong@...ux-vs.org,
	heiko.carstens@...ibm.com, linux-kernel@...r.kernel.org,
	ak@...e.de, cfriesen@...tel.com, netdev@...r.kernel.org,
	horms@...ge.net.au, akpm@...ux-foundation.org,
	linux-arch@...r.kernel.org, torvalds@...ux-foundation.org,
	schwidefsky@...ibm.com, davem@...emloft.net, zlynx@....org,
	rpjday@...dspring.com, jesper.juhl@...il.com
Subject: Re: [PATCH 24/24] document volatile atomic_read() behavior

> Historically this has been
> +accomplished by declaring the counter itself to be volatile, but the
> +ambiguity of the C standard on the semantics of volatile make this 
> practice
> +vulnerable to overly creative interpretation by compilers.

It's even worse when accessing through a volatile casted pointer;
see for example the recent(*) GCC bugs in that area.

(*) Well, not _all_ that recent.  No one should be using the 3.x
series anymore, right?

> Explicit
> +casting in atomic_read() ensures consistent behavior across 
> architectures
> +and compilers.

Even modulo compiler bugs, what makes you believe that?


Segher

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