From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DA837C04AB5 for ; Thu, 6 Jun 2019 06:14:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B175F2064A for ; Thu, 6 Jun 2019 06:14:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726631AbfFFGOz (ORCPT ); Thu, 6 Jun 2019 02:14:55 -0400 Received: from helcar.hmeau.com ([216.24.177.18]:36354 "EHLO deadmen.hmeau.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725267AbfFFGOz (ORCPT ); Thu, 6 Jun 2019 02:14:55 -0400 Received: from gondobar.mordor.me.apana.org.au ([192.168.128.4] helo=gondobar) by deadmen.hmeau.com with esmtps (Exim 4.89 #2 (Debian)) id 1hYlfi-0006IW-UG; Thu, 06 Jun 2019 14:14:47 +0800 Received: from herbert by gondobar with local (Exim 4.89) (envelope-from ) id 1hYlfa-0003iA-FC; Thu, 06 Jun 2019 14:14:38 +0800 Date: Thu, 6 Jun 2019 14:14:38 +0800 From: Herbert Xu To: "Paul E. McKenney" Cc: Alan Stern , Boqun Feng , Linus Torvalds , Frederic Weisbecker , Fengguang Wu , LKP , LKML , Netdev , "David S. Miller" , Andrea Parri , Luc Maranget , Jade Alglave Subject: Re: rcu_read_lock lost its compiler barrier Message-ID: <20190606061438.nyzaeppdbqjt3jbp@gondor.apana.org.au> References: <20190603200301.GM28207@linux.ibm.com> <20190606045109.zjfxxbkzq4wb64bj@gondor.apana.org.au> <20190606060511.GA28207@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190606060511.GA28207@linux.ibm.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 05, 2019 at 11:05:11PM -0700, Paul E. McKenney wrote: > > In case you were wondering, the reason that I was giving you such > a hard time was that from what I could see, you were pushing for no > {READ,WRITE}_ONCE() at all. ;-) Hmm, that's exactly what it should be in net/ipv4/inet_fragment.c. We don't need the READ_ONCE/WRITE_ONCE (or volatile marking) at all. Even if the compiler dices and slices the reads/writes of "a" into a thousand pieces, it should still work if the RCU primitives are worth their salt. But I do concede that in the general RCU case you must have the READ_ONCE/WRITE_ONCE calls for rcu_dereference/rcu_assign_pointer. Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt