From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752721AbaLDAMu (ORCPT ); Wed, 3 Dec 2014 19:12:50 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:49534 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750840AbaLDAMs (ORCPT ); Wed, 3 Dec 2014 19:12:48 -0500 Date: Wed, 3 Dec 2014 16:12:43 -0800 From: "Paul E. McKenney" To: Christian Borntraeger Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, torvalds@linux-foundation.org Subject: Re: [PATCH 8/9] s390/kvm: REPLACE ACCESS_ONCE with READ_ONCE Message-ID: <20141204001243.GE25340@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1417645821-54731-1-git-send-email-borntraeger@de.ibm.com> <1417645821-54731-9-git-send-email-borntraeger@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1417645821-54731-9-git-send-email-borntraeger@de.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14120400-0005-0000-0000-000006D697D9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 03, 2014 at 11:30:20PM +0100, Christian Borntraeger wrote: > 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 ipte lock code to replace ACCESS_ONCE with READ_ONCE. > > Signed-off-by: Christian Borntraeger Acked-by: Paul E. McKenney > --- > arch/s390/kvm/gaccess.c | 14 ++++++++------ > 1 file changed, 8 insertions(+), 6 deletions(-) > > diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c > index 0f961a1..8f195fa 100644 > --- a/arch/s390/kvm/gaccess.c > +++ b/arch/s390/kvm/gaccess.c > @@ -229,10 +229,10 @@ static void ipte_lock_simple(struct kvm_vcpu *vcpu) > goto out; > ic = &vcpu->kvm->arch.sca->ipte_control; > do { > - old = ACCESS_ONCE(*ic); > + old = READ_ONCE(*ic); > while (old.k) { > cond_resched(); > - old = ACCESS_ONCE(*ic); > + old = READ_ONCE(*ic); > } > new = old; > new.k = 1; > @@ -251,7 +251,8 @@ static void ipte_unlock_simple(struct kvm_vcpu *vcpu) > goto out; > ic = &vcpu->kvm->arch.sca->ipte_control; > do { > - new = old = ACCESS_ONCE(*ic); > + old = READ_ONCE(*ic); > + new = old; > new.k = 0; > } while (cmpxchg(&ic->val, old.val, new.val) != old.val); > wake_up(&vcpu->kvm->arch.ipte_wq); > @@ -265,10 +266,10 @@ static void ipte_lock_siif(struct kvm_vcpu *vcpu) > > ic = &vcpu->kvm->arch.sca->ipte_control; > do { > - old = ACCESS_ONCE(*ic); > + old = READ_ONCE(*ic); > while (old.kg) { > cond_resched(); > - old = ACCESS_ONCE(*ic); > + old = READ_ONCE(*ic); > } > new = old; > new.k = 1; > @@ -282,7 +283,8 @@ static void ipte_unlock_siif(struct kvm_vcpu *vcpu) > > ic = &vcpu->kvm->arch.sca->ipte_control; > do { > - new = old = ACCESS_ONCE(*ic); > + old = READ_ONCE(*ic); > + new = old; > new.kh--; > if (!new.kh) > new.k = 0; > -- > 1.9.3 >