From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Tue, 25 Nov 2014 21:29:14 +0100 (CET) Received: from e06smtp13.uk.ibm.com ([195.75.94.109]:41758 "EHLO e06smtp13.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S27007083AbaKYU3MQX6BL (ORCPT ); Tue, 25 Nov 2014 21:29:12 +0100 Received: from /spool/local by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 25 Nov 2014 20:29:06 -0000 Received: from d06dlp02.portsmouth.uk.ibm.com (9.149.20.14) by e06smtp13.uk.ibm.com (192.168.101.143) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Tue, 25 Nov 2014 20:29:04 -0000 Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id 404AD219004D for ; Tue, 25 Nov 2014 20:28:36 +0000 (GMT) Received: from d06av06.portsmouth.uk.ibm.com (d06av06.portsmouth.uk.ibm.com [9.149.37.217]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id sAPKT3Lh58851350 for ; Tue, 25 Nov 2014 20:29:03 GMT Received: from d06av06.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av06.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id sAPFQ6Jn006620 for ; Tue, 25 Nov 2014 10:26:06 -0500 Received: from oc1450873852.ibm.com (sig-9-79-63-245.de.ibm.com [9.79.63.245]) by d06av06.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVin) with ESMTP id sAPFQ5ff006562; Tue, 25 Nov 2014 10:26:05 -0500 Message-ID: <5474E68D.4010707@de.ibm.com> Date: Tue, 25 Nov 2014 21:29:01 +0100 From: Christian Borntraeger User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: linux-kernel@vger.kernel.org CC: 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 , Alexei Starovoitov , David Howells , Russell King Subject: Re: [PATCHv2 04/10] x86/spinlock: Replace ACCESS_ONCE with READ_ONCE/ASSIGN_ONCE References: <1416919117-50652-1-git-send-email-borntraeger@de.ibm.com> <1416919117-50652-5-git-send-email-borntraeger@de.ibm.com> In-Reply-To: <1416919117-50652-5-git-send-email-borntraeger@de.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14112520-0013-0000-0000-000001FC808C 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: 44448 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: borntraeger@de.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 Am 25.11.2014 um 13:38 schrieb Christian Borntraeger: > ACCESS_ONCE does not work reliably on non-scalar types. For > example gcc 4.6 and 4.7 might remove the volatile tag for such > accesses during the SRA (scalar replacement of aggregates) step > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) > > Change the spinlock code to replace ACCESS_ONCE with READ_ONCE > and ASSIGN_ONCE. > > Signed-off-by: Christian Borntraeger > --- > arch/x86/include/asm/spinlock.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h > index 9295016..af6e673 100644 > --- a/arch/x86/include/asm/spinlock.h > +++ b/arch/x86/include/asm/spinlock.h > @@ -92,7 +92,7 @@ static __always_inline void arch_spin_lock(arch_spinlock_t *lock) > unsigned count = SPIN_THRESHOLD; > > do { > - if (ACCESS_ONCE(lock->tickets.head) == inc.tail) > + if (ASSIGN_ONCE(inc.tail, lock->tickets.head)) As Mike pointed out: this should be if (READ_ONCE(lock->tickets.head) == inc.tail) of course.