From owner-svn-src-all@FreeBSD.ORG Thu Apr 2 14:01:02 2015 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 2ACD7C0A; Thu, 2 Apr 2015 14:01:02 +0000 (UTC) Received: from relay.mailchannels.net (tkt-001-i373.relay.mailchannels.net [174.136.5.175]) by mx1.freebsd.org (Postfix) with ESMTP id 8DC1B8E7; Thu, 2 Apr 2015 14:01:00 +0000 (UTC) X-Sender-Id: duocircle|x-authuser|hippie Received: from smtp5.ore.mailhop.org (ip-10-220-9-73.us-west-2.compute.internal [10.220.9.73]) by relay.mailchannels.net (Postfix) with ESMTPA id D90801001AF; Thu, 2 Apr 2015 13:53:21 +0000 (UTC) X-Sender-Id: duocircle|x-authuser|hippie Received: from smtp5.ore.mailhop.org (smtp5.ore.mailhop.org [10.21.145.197]) (using TLSv1 with cipher DHE-RSA-AES256-SHA) by 0.0.0.0:2500 (trex/5.4.8); Thu, 02 Apr 2015 13:53:22 +0000 X-MC-Relay: Neutral X-MailChannels-SenderId: duocircle|x-authuser|hippie X-MailChannels-Auth-Id: duocircle X-MC-Loop-Signature: 1427982801982:177892084 X-MC-Ingress-Time: 1427982801982 Received: from c-73-34-117-227.hsd1.co.comcast.net ([73.34.117.227] helo=ilsoft.org) by smtp5.ore.mailhop.org with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.82) (envelope-from ) id 1YdfYb-0005Sp-8K; Thu, 02 Apr 2015 13:53:17 +0000 Received: from revolution.hippie.lan (revolution.hippie.lan [172.22.42.240]) by ilsoft.org (8.14.9/8.14.9) with ESMTP id t32Dr77w063902; Thu, 2 Apr 2015 07:53:07 -0600 (MDT) (envelope-from ian@freebsd.org) X-Mail-Handler: DuoCircle Outbound SMTP X-Originating-IP: 73.34.117.227 X-Report-Abuse-To: abuse@duocircle.com (see https://support.duocircle.com/support/solutions/articles/5000540958-duocircle-standard-smtp-abuse-information for abuse reporting information) X-MHO-User: U2FsdGVkX1+Acop99Wjzl9pyVlOCYvy9 Message-ID: <1427982787.82583.111.camel@freebsd.org> Subject: Re: svn commit: r280971 - in head: contrib/ipfilter/tools share/man/man4 sys/contrib/ipfilter/netinet sys/netinet sys/netipsec sys/netpfil/pf From: Ian Lepore To: Gleb Smirnoff Date: Thu, 02 Apr 2015 07:53:07 -0600 In-Reply-To: <20150402123522.GC64665@FreeBSD.org> References: <201504012226.t31MQedN044443@svn.freebsd.org> <1427929676.82583.103.camel@freebsd.org> <20150402123522.GC64665@FreeBSD.org> Content-Type: text/plain; charset="us-ascii" X-Mailer: Evolution 3.12.10 FreeBSD GNOME Team Port Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-AuthUser: hippie Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 02 Apr 2015 14:01:02 -0000 On Thu, 2015-04-02 at 15:35 +0300, Gleb Smirnoff wrote: > On Wed, Apr 01, 2015 at 05:07:56PM -0600, Ian Lepore wrote: > I> > Author: glebius > I> > Date: Wed Apr 1 22:26:39 2015 > I> > New Revision: 280971 > I> > URL: https://svnweb.freebsd.org/changeset/base/280971 > I> > > I> > Log: > I> > o Use new function ip_fillid() in all places throughout the kernel, > I> > where we want to create a new IP datagram. > I> > o Add support for RFC6864, which allows to set IP ID for atomic IP > I> > datagrams to any value, to improve performance. The behaviour is > I> > controlled by net.inet.ip.rfc6864 sysctl knob, which is enabled by > I> > default. > I> > o In case if we generate IP ID, use counter(9) to improve performance. > I> > o Gather all code related to IP ID into ip_id.c. > I> > > I> > Differential Revision: https://reviews.freebsd.org/D2177 > I> > Reviewed by: adrian, cy, rpaulo > I> > Tested by: Emeric POUPON > I> > Sponsored by: Netflix > I> > Sponsored by: Nginx, Inc. > I> > Relnotes: yes > I> > > I> [...] > I> > +void > I> > +ip_fillid(struct ip *ip) > I> > +{ > I> > + > I> > + /* > I> > + * Per RFC6864 Section 4 > I> > + * > I> > + * o Atomic datagrams: (DF==1) && (MF==0) && (frag_offset==0) > I> > + * o Non-atomic datagrams: (DF==0) || (MF==1) || (frag_offset>0) > I> > + */ > I> > + if (V_ip_rfc6864 && (ip->ip_off & htons(IP_DF)) == htons(IP_DF)) > I> > + ip->ip_id = 0; > I> > + else if (V_ip_do_randomid) > I> > + ip->ip_id = ip_randomid(); > I> > + else { > I> > + counter_u64_add(V_ip_id, 1); > I> > + ip->ip_id = htons((*(uint64_t *)zpcpu_get(V_ip_id)) & 0xffff); > I> > + } > I> > +} > I> > + > I> > I> This is completely bogus. It's a big opacity violation (it relies on > I> what should be opaque private internal implementation details of > I> counter(9)). The fact that the counter api doesn't provide a function > I> for retrieving one cpu's counter value should be a big clue there -- the > I> fact that you know the internals doesn't make it okay to reach behind > I> the counter and grab a value like that. It may not even be safe to do > I> so on any given architecture; it certainly isn't safe on arm, and that > I> line of code above will work only by accident because you're throwing > I> way all but 16 bits. > > I though about providing that API, but since it isn't safe in general, > I decided to not do that. > > I> But even more importantly, this WILL result in multiple threads using > I> the same value at the same time... > I> > I> - Thread A on CPU 1 and thread B on CPU 2 both begin executing here at > I> the same time, and both get through counter_u64_add(). > I> - Thread A keeps running and uses CPU 1's new value, call it 27. > I> - Thread B gets prempted between counter_u64_add() and zpcpu_get(). > I> When it resumes it's now on CPU 1, so it retrieves value 27 as well. > > This was already discussed in this thread: > > https://lists.freebsd.org/pipermail/svn-src-head/2015-March/069864.html > Discussed, but not really resolved, or even reasonably addressed. But I guess if you think it's done, more words at this point aren't going to make you see the problems clearly enough to make the required changes. -- Ian