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Date: Fri, 5 Sep 2014 22:48:34 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: bit fields && data tearing
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Cc: Jakub Jelinek <jakub@redhat.com>,
 "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
 Tony Luck <tony.luck@intel.com>,
 "linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
 Peter Hurley <peter@hurleysoftware.com>, Michael Cree <mcree@orcon.net.nz>,
 "linux-alpha@vger.kernel.org" <linux-alpha@vger.kernel.org>,
 Oleg Nesterov <oleg@redhat.com>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 Marc Gauthier <marc@cadence.com>, Paul Mackerras <paulus@samba.org>,
 "H. Peter Anvin" <hpa@zytor.com>, David Laight <David.Laight@ACULAB.COM>,
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On Fri, 5 Sep 2014, Paul E. McKenney wrote:
> On Fri, Sep 05, 2014 at 01:34:52PM -0700, H. Peter Anvin wrote:
> > On 09/05/2014 01:14 PM, Peter Hurley wrote:
> > > 
> > > Here's how I read the two statements.
> > > 
> > > First, the commit message:
> > > 
> > > "It [this commit] documents that CPUs [supported by the Linux kernel]
> > > _must provide_ atomic one-byte and two-byte naturally aligned loads and stores."
> > > 
> > > 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."
> > > 
> > 
> > Does this apply in general or only to SMP configurations?  I guess
> > non-SMP configurations would still have problems if interrupted in the
> > wrong place...
> 
> And preemption could cause problems, too.  So I believe that it needs
> to be universal.

Well preemption is usually caused by an interrupt, except you have a
combined load and preempt instruction :)

Thanks,

	tglx