From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754662Ab3KUTnt (ORCPT ); Thu, 21 Nov 2013 14:43:49 -0500 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:39868 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751395Ab3KUTns (ORCPT ); Thu, 21 Nov 2013 14:43:48 -0500 X-Originating-IP: 173.246.103.110 Date: Thu, 21 Nov 2013 11:43:35 -0800 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu Subject: Re: [PATCH RFC tip/core/rcu 1/3] documentation: Add needed ACCESS_ONCE() calls to memory-barriers.txt Message-ID: <20131121194334.GC14144@jtriplet-mobl1> References: <20131121174824.GA6611@linux.vnet.ibm.com> <1385056127-6980-1-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1385056127-6980-1-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 21, 2013 at 09:48:45AM -0800, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > The Documentation/memory-barriers.txt file was written before the need > for ACCESS_ONCE() was fully appreciated. It therefore contains no > ACCESS_ONCE() calls, which can be a problem when people lift examples > from it. This commit therefore adds ACCESS_ONCE() calls. > > Signed-off-by: Paul E. McKenney > Cc: David Howells > --- > Documentation/memory-barriers.txt | 204 +++++++++++++++++++++++--------------- > 1 file changed, 124 insertions(+), 80 deletions(-) > > diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt > index c8c42e64e953..eccc83a40ce1 100644 > --- a/Documentation/memory-barriers.txt > +++ b/Documentation/memory-barriers.txt > @@ -194,18 +194,20 @@ There are some minimal guarantees that may be expected of a CPU: > (*) On any given CPU, dependent memory accesses will be issued in order, with > respect to itself. This means that for: > > - Q = P; D = *Q; > + ACCESS_ONCE(Q) = P; smp_memory_barrier_depends(); D = ACCESS_ONCE(*Q); That should be smp_read_barrier_depends(). Also, most of the time shouldn't that use rcu_dereference rather than a raw smp_read_barrier_depends()? - Josh Triplett