From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH RFC tip/core/rcu 14/15] netfilter: Remove now-redundant smp_read_barrier_depends() Date: Tue, 10 Oct 2017 08:56:50 -0700 Message-ID: <20171010155650.GF3521@linux.vnet.ibm.com> References: <20171010001951.GA6476@linux.vnet.ibm.com> <1507594969-8347-14-git-send-email-paulmck@linux.vnet.ibm.com> <20171010084334.nbyhryiwyrl6km4u@hirez.programming.kicks-ass.net> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:36056 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932271AbdJJP45 (ORCPT ); Tue, 10 Oct 2017 11:56:57 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9AFu3Wk194396 for ; Tue, 10 Oct 2017 11:56:56 -0400 Received: from e18.ny.us.ibm.com (e18.ny.us.ibm.com [129.33.205.208]) by mx0b-001b2d01.pphosted.com with ESMTP id 2dgwesewvu-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 10 Oct 2017 11:56:56 -0400 Received: from localhost by e18.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 10 Oct 2017 11:56:55 -0400 Content-Disposition: inline In-Reply-To: <20171010084334.nbyhryiwyrl6km4u@hirez.programming.kicks-ass.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, torvalds@linux-foundation.org, mark.rutland@arm.com, dhowells@redhat.com, linux-arch@vger.kernel.org, will.deacon@arm.com, Pablo Neira Ayuso , Jozsef Kadlecsik , Florian Westphal , "David S. Miller" , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org On Tue, Oct 10, 2017 at 10:43:34AM +0200, Peter Zijlstra wrote: > On Mon, Oct 09, 2017 at 05:22:48PM -0700, Paul E. McKenney wrote: > > READ_ONCE() now implies smp_read_barrier_depends(), which means that > > the instances in arpt_do_table(), ipt_do_table(), and ip6t_do_table() > > are now redundant. This commit removes them and adjusts the comments. > > Similar to the previous patch, the lack of READ_ONCE() in the original > code is a pre-existing bug. It would allow the compiler to tear the load > and observe a composite of two difference pointer values, or reload the > private pointer and result in table_base and jumpstacl being part of > different objects. > > It would be good to point out this actually fixes a bug in the code. Assuming that these changes actually fixed something, agreed. ;-) Thanx, Paul