linux-kernel - Re: [patch] Re: using long instead of atomic

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Date:	Mon, 3 Mar 2008 15:48:31 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Pavel Machek <pavel@....cz>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...l.org>,
	Zdenek Kabelac <zdenek.kabelac@...il.com>, davem@...emloft.net,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Pierre Ossman <drzeus-mmc@...eus.cx>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [patch] Re: using long instead of atomic_t when only set/read
 is required

> Ok, so linux actually atomicity of long?

No it doesn't. And even if it did you couldn't use long for this because
atomic_t also ensures the points operations complete are defined. You
might just about get away with volatile long * objects on x86 for simple
assignments but for anything else gcc can and will generate code to
update values whichever way it feels best - which includes turning

	long *x = a + b;

into

	*x = a;
	*x += b;

Alan
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