From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756098AbdJJJg5 (ORCPT ); Tue, 10 Oct 2017 05:36:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52056 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755221AbdJJJgz (ORCPT ); Tue, 10 Oct 2017 05:36:55 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 9058E81DF0 Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=dhowells@redhat.com Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20171010083948.5s6bmggp3cyqtkrf@hirez.programming.kicks-ass.net> References: <20171010083948.5s6bmggp3cyqtkrf@hirez.programming.kicks-ass.net> <20171010001951.GA6476@linux.vnet.ibm.com> <1507594969-8347-12-git-send-email-paulmck@linux.vnet.ibm.com> To: Peter Zijlstra Cc: dhowells@redhat.com, "Paul E. McKenney" , linux-kernel@vger.kernel.org, mingo@kernel.org, torvalds@linux-foundation.org, mark.rutland@arm.com, linux-arch@vger.kernel.org, will.deacon@arm.com, Jonathan Corbet , Alexander Kuleshov Subject: Re: [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends() MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <8103.1507628212.1@warthog.procyon.org.uk> Date: Tue, 10 Oct 2017 10:36:52 +0100 Message-ID: <8104.1507628212@warthog.procyon.org.uk> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Tue, 10 Oct 2017 09:36:55 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra wrote: > > Now that smp_read_barrier_depends() is implied by READ_ONCE(), adding > > READ_ONCE() to assoc_array_ptr_to_leaf() and __assoc_array_ptr_to_meta() > > allows the several smp_read_barrier_depends() calls to be removed from > > lib/assoc_array.c. This commit makes this change. > > So arguably this code was broken for not already having READ_ONCE(). No, the code is right; this is the wrong place to use READ_ONCE(). The callers already call READ_ONCE() or ACCESS_ONCE(). David