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=-5.2 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 DCF54C433E7 for ; Fri, 16 Oct 2020 15:28:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7DE27207C4 for ; Fri, 16 Oct 2020 15:28:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2395483AbgJPP24 (ORCPT ); Fri, 16 Oct 2020 11:28:56 -0400 Received: from correo.us.es ([193.147.175.20]:51156 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2395234AbgJPP2z (ORCPT ); Fri, 16 Oct 2020 11:28:55 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id DB0F7DA388 for ; Fri, 16 Oct 2020 17:28:52 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id CC8FFDA791 for ; Fri, 16 Oct 2020 17:28:52 +0200 (CEST) Received: by antivirus1-rhel7.int (Postfix, from userid 99) id C1DA4DA78D; Fri, 16 Oct 2020 17:28:52 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 8B851DA704; Fri, 16 Oct 2020 17:28:50 +0200 (CEST) Received: from 192.168.1.97 (192.168.1.97) by antivirus1-rhel7.int (F-Secure/fsigk_smtp/550/antivirus1-rhel7.int); Fri, 16 Oct 2020 17:28:50 +0200 (CEST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/antivirus1-rhel7.int) Received: from us.es (unknown [90.77.255.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: 1984lsi) by entrada.int (Postfix) with ESMTPSA id 6F7AA42EE38E; Fri, 16 Oct 2020 17:28:50 +0200 (CEST) Date: Fri, 16 Oct 2020 17:28:50 +0200 X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: Phil Sutter , netfilter-devel@vger.kernel.org, Florian Westphal Subject: Re: [iptables PATCH 3/3] nft: Fix for concurrent noflush restore calls Message-ID: <20201016152850.GA1416@salvia> References: <20201005144858.11578-1-phil@nwl.cc> <20201005144858.11578-4-phil@nwl.cc> <20201012125450.GA26934@salvia> <20201013100803.GW13016@orbyte.nwl.cc> <20201013101502.GA29142@salvia> <20201014094640.GA13016@orbyte.nwl.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201014094640.GA13016@orbyte.nwl.cc> User-Agent: Mutt/1.10.1 (2018-07-13) X-Virus-Scanned: ClamAV using ClamSMTP Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Wed, Oct 14, 2020 at 11:46:40AM +0200, Phil Sutter wrote: > On Tue, Oct 13, 2020 at 12:15:02PM +0200, Pablo Neira Ayuso wrote: > > On Tue, Oct 13, 2020 at 12:08:03PM +0200, Phil Sutter wrote: > > [...] > > > On Mon, Oct 12, 2020 at 02:54:50PM +0200, Pablo Neira Ayuso wrote: > > > [...] > > > > Patch LGTM, thanks Phil. > > > > > > > > What I don't clearly see yet is what scenario is triggering the bug in > > > > the existing code, if you don't mind to explain. > > > > > > See the test case attached to the patch: An other iptables-restore > > > process may add references (i.e., jumps) to a chain the own > > > iptables-restore process wants to delete. This should not be a problem > > > because these references are added to a chain that is being flushed by > > > the own process as well. But if that chain doesn't exist while the own > > > process fetches kernel's ruleset, this flush job is not created. > > > > Let me rephrase this: > > > > 1) process A fetches the ruleset, finds no chain C (no flush job then) > > 2) process B adds new chain C, flush job is present > > 3) process B adds the ruleset > > 4) process A appends rules to the existing chain C (because there is > > no flush job) > > > > Is this the scenario? If so, I wonder why the generation ID is not > > helping to refresh and retry. > > Not quite, let me try to put this more clearly: > > * Dump A: > | *filter > | :FOO - [0:0] # flush chain FOO > | -X BAR # remove chain BAR > | COMMIT > > * Dump B: > | *filter > | -A FOO -j BAR # reference BAR from a rule in FOO > | COMMIT > > * Kernel ruleset: > | *filter > | :BAR - [0:0] > | COMMIT > > * Process A: > * read dump A > * fetch cache > > * Process B: > * read dump B > * fetch ruleset > * commit to kernel > > * Process A: > * skip flush chain FOO job: not present > * add delete chain BAR job: chain exists > * commit fails (genid outdated) > * refresh transaction: > * delete chain BAR job remains active > * genid updated > * commit fails: can't remove chain BAR: EBUSY Makes sense. Thanks a lot for explaining. Probably you can include this in the commit description for the record. > I realize the test case is not quite effective, ruleset should be > emptied upon each iteration of concurrent restore job startup. Please, update the test and revamp.