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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 6D121C433E0 for ; Tue, 9 Mar 2021 11:34:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 32C3E65253 for ; Tue, 9 Mar 2021 11:34:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229764AbhCILeP (ORCPT ); Tue, 9 Mar 2021 06:34:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229980AbhCILeD (ORCPT ); Tue, 9 Mar 2021 06:34:03 -0500 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [IPv6:2a0a:51c0:0:12e:520::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 15E80C06174A; Tue, 9 Mar 2021 03:34:03 -0800 (PST) Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1lJacW-0005aP-OH; Tue, 09 Mar 2021 12:33:48 +0100 Date: Tue, 9 Mar 2021 12:33:48 +0100 From: Florian Westphal To: Mark Tomlinson Cc: pablo@netfilter.org, kadlec@netfilter.org, fw@strlen.de, subashab@codeaurora.org, netfilter-devel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/3] netfilter: x_tables: Use correct memory barriers. Message-ID: <20210309113348.GE10808@breakpoint.cc> References: <20210308012413.14383-1-mark.tomlinson@alliedtelesis.co.nz> <20210308012413.14383-4-mark.tomlinson@alliedtelesis.co.nz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210308012413.14383-4-mark.tomlinson@alliedtelesis.co.nz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org Mark Tomlinson wrote: > When a new table value was assigned, it was followed by a write memory > barrier. This ensured that all writes before this point would complete > before any writes after this point. However, to determine whether the > rules are unused, the sequence counter is read. To ensure that all > writes have been done before these reads, a full memory barrier is > needed, not just a write memory barrier. The same argument applies when > incrementing the counter, before the rules are read. > > Changing to using smp_mb() instead of smp_wmb() fixes the kernel panic > reported in cc00bcaa5899 (which is still present), while still > maintaining the same speed of replacing tables. > > The smb_mb() barriers potentially slow the packet path, however testing > has shown no measurable change in performance on a 4-core MIPS64 > platform. Okay, thanks for testing. I have no further feedback.