From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753977AbaKXNbn (ORCPT ); Mon, 24 Nov 2014 08:31:43 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56536 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753448AbaKXNbl (ORCPT ); Mon, 24 Nov 2014 08:31:41 -0500 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 In-Reply-To: <1416834210-61738-8-git-send-email-borntraeger@de.ibm.com> References: <1416834210-61738-8-git-send-email-borntraeger@de.ibm.com> <1416834210-61738-1-git-send-email-borntraeger@de.ibm.com> To: Christian Borntraeger Cc: dhowells@redhat.com, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mips@linux-mips.org, linux-x86_64@vger.kernel.org, linux-s390@vger.kernel.org, Paolo Bonzini , paulmck@linux.vnet.ibm.com, mingo@kernel.org, torvalds@linux-foundation.org, Catalin Marinas , Will Deacon Subject: Re: [PATCH/RFC 7/7] kernel: Force ACCESS_ONCE to work only on scalar types MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <15470.1416835748.1@warthog.procyon.org.uk> From: David Howells Date: Mon, 24 Nov 2014 13:30:58 +0000 Message-ID: <15567.1416835858@warthog.procyon.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christian Borntraeger wrote: > +#define get_scalar_volatile_pointer(x) ({ \ > + typeof(x) *__p = &(x); \ > + volatile typeof(x) *__vp = __p; \ > + (void)(long)*__p; __vp; }) > +#define ACCESS_ONCE(x) (*get_scalar_volatile_pointer(x)) Might this cause two loads from memory under some conditions? Once for the fourth line and once for the fifth? (Apologies if this has already been discussed) David