From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE Date: Thu, 15 Jan 2015 21:01:19 +0100 Message-ID: <20150115200119.GA29684@redhat.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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <54B81A37.80109@de.ibm.com> Sender: owner-linux-mm@kvack.org To: Christian Borntraeger 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 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? Oleg. -- 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 mx1.redhat.com ([209.132.183.28]:54727 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752699AbbAOUCY (ORCPT ); Thu, 15 Jan 2015 15:02:24 -0500 Date: Thu, 15 Jan 2015 21:01:19 +0100 From: Oleg Nesterov Subject: Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE Message-ID: <20150115200119.GA29684@redhat.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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54B81A37.80109@de.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Christian Borntraeger 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: <20150115200119.i2HgqEzQbyleEcVDIwakVTW8y_umwFD96U6N3gE0Rjw@z> 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? Oleg.