From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Mon, 24 Nov 2014 20:42:17 +0100 (CET) Received: from e34.co.us.ibm.com ([32.97.110.152]:50317 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S27006921AbaKXTmMwLqIU (ORCPT ); Mon, 24 Nov 2014 20:42:12 +0100 Received: from /spool/local by e34.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 24 Nov 2014 12:42:06 -0700 Received: from d03dlp01.boulder.ibm.com (9.17.202.177) by e34.co.us.ibm.com (192.168.1.134) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Mon, 24 Nov 2014 12:42:03 -0700 Received: from b03cxnp08027.gho.boulder.ibm.com (b03cxnp08027.gho.boulder.ibm.com [9.17.130.19]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 24B461FF0045 for ; Mon, 24 Nov 2014 12:30:47 -0700 (MST) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by b03cxnp08027.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id sAOJg2qY35717134 for ; Mon, 24 Nov 2014 12:42:02 -0700 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id sAOJkuTx012850 for ; Mon, 24 Nov 2014 12:46:57 -0700 Received: from paulmck-ThinkPad-W500 ([9.50.23.142]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id sAOJkuct012845; Mon, 24 Nov 2014 12:46:56 -0700 Received: by paulmck-ThinkPad-W500 (Postfix, from userid 1000) id 7C22D381844; Mon, 24 Nov 2014 11:42:00 -0800 (PST) Date: Mon, 24 Nov 2014 11:42:00 -0800 From: "Paul E. McKenney" To: Linus Torvalds Cc: Christian Borntraeger , Alexei Starovoitov , David Howells , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , linux-mips , linux-x86_64@vger.kernel.org, linux-s390 , Paolo Bonzini , Ingo Molnar , Catalin Marinas , Will Deacon Subject: Re: [PATCH/RFC 7/7] kernel: Force ACCESS_ONCE to work only on scalar types Message-ID: <20141124194200.GR5050@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1416834210-61738-1-git-send-email-borntraeger@de.ibm.com> <1416834210-61738-8-git-send-email-borntraeger@de.ibm.com> <15567.1416835858@warthog.procyon.org.uk> <547381D7.2070404@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14112419-0017-0000-0000-0000068AFF52 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 44395 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: paulmck@linux.vnet.ibm.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Mon, Nov 24, 2014 at 11:14:42AM -0800, Linus Torvalds wrote: > On Mon, Nov 24, 2014 at 11:07 AM, Christian Borntraeger > wrote: > > > > Looks really nice, but does not work with ACCESS_ONCE is on the left-hand side: > > Oh, I forgot about that. And that was indeed why I had done that whole > helper macro originally, with ACCESS_ONCE() itself just being the > dereference of the pointer. OK, how about the following? It complains if the variable is too large, for example, long long on 32-bit systems or large structures. It is OK loading from and storing to small structures as well, which I am having a hard time thinking of as a disadvantage. Thanx, Paul ------------------------------------------------------------------------ #define get_scalar_volatile_pointer(x) ({ \ volatile typeof(x) *__vp = &(x); \ BUILD_BUG_ON(sizeof(*__vp) != sizeof(char) && \ sizeof(*__vp) != sizeof(short) && \ sizeof(*__vp) != sizeof(int) && \ sizeof(*__vp) != sizeof(long)); \ __vp; }) #define ACCESS_ONCE(x) (*get_scalar_volatile_pointer(x))