linux-kernel - Re: bit fields && data tearing

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Message-ID: <20140905203951.GA4053@omega>
Date:	Sat, 6 Sep 2014 08:39:51 +1200
From:	Michael Cree <mcree@...on.net.nz>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Marc Gauthier <marc@...ence.com>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Laight <David.Laight@...LAB.COM>,
	Jakub Jelinek <jakub@...hat.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Tony Luck <tony.luck@...el.com>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Miroslav Franc <mfranc@...hat.com>,
	Richard Henderson <rth@...ddle.net>,
	"linux-alpha@...r.kernel.org" <linux-alpha@...r.kernel.org>
Subject: Re: bit fields && data tearing

On Fri, Sep 05, 2014 at 04:14:48PM -0400, Peter Hurley wrote:
> Second, in the body of the document:
> 
> "The Linux kernel no longer supports pre-EV56 Alpha CPUs, because these
> older CPUs _do not provide_ atomic one-byte and two-byte loads and stores."

Let's be clear here, the pre-EV56 Alpha CPUs do provide an atomic
one-byte and two-byte load and store; it's just that one must use
locked load and store sequences to achieve atomicity.  The point,
I think, is that the pre-EV56 Alpha CPUs provide non-atomic one-byte
and two-byte load and stores as the norm, and that is the problem.

Cheers
Michael.
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