From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933022AbcBPQiD (ORCPT ); Tue, 16 Feb 2016 11:38:03 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:47077 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751477AbcBPQiB (ORCPT ); Tue, 16 Feb 2016 11:38:01 -0500 Subject: Re: [PATCH 1/3] tools/liblockdep: add userspace version of READ_ONCE To: Peter Zijlstra , Alfredo Alvarez Fernandez References: <1455147212-2389-1-git-send-email-alfredoalvarezernandez@gmail.com> <1455147212-2389-2-git-send-email-alfredoalvarezernandez@gmail.com> <20160211151610.GL6357@twins.programming.kicks-ass.net> Cc: mingo@redhat.com, linux-kernel@vger.kernel.org From: Sasha Levin Message-ID: <56C3504A.5040301@oracle.com> Date: Tue, 16 Feb 2016 11:37:30 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 MIME-Version: 1.0 In-Reply-To: <20160211151610.GL6357@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/11/2016 10:16 AM, Peter Zijlstra wrote: > On Thu, Feb 11, 2016 at 12:33:30AM +0100, Alfredo Alvarez Fernandez wrote: >> From: Alfredo Alvarez Fernandez >> >> This was added to the kernel code in 1658d35ead5d ("list: Use >> READ_ONCE() when testing for empty lists") >> There's nothing special we need to do about it in userspace. >> >> Signed-off-by: Alfredo Alvarez Fernandez >> --- >> tools/lib/lockdep/uinclude/linux/compiler.h | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/tools/lib/lockdep/uinclude/linux/compiler.h b/tools/lib/lockdep/uinclude/linux/compiler.h >> index 6386dc3..fd3e56a 100644 >> --- a/tools/lib/lockdep/uinclude/linux/compiler.h >> +++ b/tools/lib/lockdep/uinclude/linux/compiler.h >> @@ -3,6 +3,7 @@ >> >> #define __used __attribute__((__unused__)) >> #define unlikely >> +#define READ_ONCE(x) (x) >> #define WRITE_ONCE(x, val) x=(val) > > I would argue we'd still very much want the volatile cast for both READ > and WRITE_ONCE(). > > Why do these things have different semantics between user and kernel > space? You're right. I'll send a patch. Thanks, Sasha