From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE Date: Thu, 15 Jan 2015 22:00:59 +0100 Message-ID: <54B82A8B.7000809@de.ibm.com> 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> <54B81A37.80109@de.ibm.com> <20150115200119.GA29684@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150115200119.GA29684@redhat.com> Sender: owner-linux-mm@kvack.org 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 List-Id: linux-arch.vger.kernel.org Am 15.01.2015 um 21:01 schrieb Oleg Nesterov: > On 01/15, Christian Borntraeger wrote: >> >> 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 > > I understand, but READ_ONCE(lock->tickets.head) looks better anyway and > arch_spin_lock() already use READ_ONCE() for this. > > So why we should keep the last ACCESS_ONCE() in spinlock.h ? Just to make > another cosmetic cleanup which touches the same function later? OK, I will change that one as well. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e06smtp10.uk.ibm.com ([195.75.94.106]:42514 "EHLO e06smtp10.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751566AbbAOVBE (ORCPT ); Thu, 15 Jan 2015 16:01:04 -0500 Received: from /spool/local by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 15 Jan 2015 21:01:03 -0000 Message-ID: <54B82A8B.7000809@de.ibm.com> Date: Thu, 15 Jan 2015 22:00:59 +0100 From: Christian Borntraeger MIME-Version: 1.0 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> <54B81A37.80109@de.ibm.com> <20150115200119.GA29684@redhat.com> In-Reply-To: <20150115200119.GA29684@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: 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 Message-ID: <20150115210059.MLPEAhMiyM_cz5y0ClK77mKj7-4SNYfrGJAiBGOW9_w@z> Am 15.01.2015 um 21:01 schrieb Oleg Nesterov: > On 01/15, Christian Borntraeger wrote: >> >> 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 > > I understand, but READ_ONCE(lock->tickets.head) looks better anyway and > arch_spin_lock() already use READ_ONCE() for this. > > So why we should keep the last ACCESS_ONCE() in spinlock.h ? Just to make > another cosmetic cleanup which touches the same function later? OK, I will change that one as well.