From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Date: Thu, 15 Jan 2015 21:00:59 +0000 Subject: Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE Message-Id: <54B82A8B.7000809@de.ibm.com> List-Id: 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> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 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.