From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754206AbbAOTv1 (ORCPT ); Thu, 15 Jan 2015 14:51:27 -0500 Received: from e06smtp16.uk.ibm.com ([195.75.94.112]:52440 "EHLO e06smtp16.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751566AbbAOTvZ (ORCPT ); Thu, 15 Jan 2015 14:51:25 -0500 Message-ID: <54B81A37.80109@de.ibm.com> Date: Thu, 15 Jan 2015 20:51:19 +0100 From: Christian Borntraeger User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Oleg Nesterov CC: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, xen-devel@lists.xenproject.org, linux-mm@kvack.org Subject: Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE References: <1421312314-72330-1-git-send-email-borntraeger@de.ibm.com> <1421312314-72330-5-git-send-email-borntraeger@de.ibm.com> <20150115193839.GA28727@redhat.com> In-Reply-To: <20150115193839.GA28727@redhat.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: 15011519-0025-0000-0000-00000365BBDA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 15.01.2015 um 20:38 schrieb Oleg Nesterov: > On 01/15, Christian Borntraeger wrote: >> >> --- a/arch/x86/include/asm/spinlock.h >> +++ b/arch/x86/include/asm/spinlock.h >> @@ -186,7 +186,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock) >> __ticket_t head = ACCESS_ONCE(lock->tickets.head); >> >> for (;;) { >> - struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets); >> + struct __raw_tickets tmp = READ_ONCE(lock->tickets); > > Agreed, but what about another ACCESS_ONCE() above? > > Oleg. > tickets.head is a scalar type, so ACCESS_ONCE does work fine with gcc 4.6/4.7. My goal was to convert all accesses on non-scalar types as until "kernel: tighten rules for ACCESS ONCE" is merged because anything else would be a Whac-a-mole like adventure (I learned that during the last round in next: all conversions in this series fix up changes made during this merge window) We probably going to do a bigger bunch of bulk conversion later on when "kernel: tighten rules for ACCESS ONCE" prevents new problems. Makes sense? Christian