Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752786AbdLESkC (ORCPT ); Tue, 5 Dec 2017 13:40:02 -0500 Received: from bombadil.infradead.org ([65.50.211.133]:50077 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751937AbdLESkB (ORCPT ); Tue, 5 Dec 2017 13:40:01 -0500 Date: Tue, 5 Dec 2017 19:39:46 +0100 From: Peter Zijlstra To: "Michael S. Tsirkin" Cc: "Paul E. McKenney" , linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, Jason Wang , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: Re: [PATCH tip/core/rcu 21/21] drivers/vhost: Remove now-redundant read_barrier_depends() Message-ID: <20171205183946.GP3165@worktop.lehotels.local> References: <20171201195053.GA23494@linux.vnet.ibm.com> <1512157876-24665-21-git-send-email-paulmck@linux.vnet.ibm.com> <20171205202928-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171205202928-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 472 Lines: 11 On Tue, Dec 05, 2017 at 08:31:20PM +0200, Michael S. Tsirkin wrote: > Apropos, READ_ONCE is now asymmetrical with WRITE_ONCE. > > I can read a pointer with READ_ONCE and be sure the value > is sane, but only if I also remember to put in smp_wmb before > WRITE_ONCE. Otherwise the pointer is ok but no guarantees > about the data pointed to. That was already the case on everything except Alpha. And the canonical match do the data dependency is store_release, not wmb.