From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [RFC PATCH net 3/4] ipv6: datagram: Update dst cache of a connected datagram sk during pmtu update Date: Tue, 05 Apr 2016 19:56:54 -0400 (EDT) Message-ID: <20160405.195654.681016570979164308.davem@davemloft.net> References: <20160403023349.GA57008@lichen-mbp.local.DHCP.thefacebook.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: kafai@fb.com, netdev@vger.kernel.org, edumazet@google.com, weiwan@google.com, kernel-team@fb.com To: xiyou.wangcong@gmail.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:35111 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753459AbcDEX45 (ORCPT ); Tue, 5 Apr 2016 19:56:57 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: From: Cong Wang Date: Mon, 4 Apr 2016 13:45:02 -0700 > On Sat, Apr 2, 2016 at 7:33 PM, Martin KaFai Lau wrote: >> One thing to note is that this patch uses the addresses from the sk >> instead of iph when updating sk->sk_dst_cache. It is basically the >> same logic that the __ip6_datagram_connect() is doing, so some >> refactoring works in the first two patches. >> >> AFAIK, a UDP socket can become connected after sending out some >> datagrams in un-connected state. or It can be connected >> multiple times to different destinations. I did some quick >> tests but I could be wrong. >> >> I am thinking if there could be a chance that the skb->data, which >> has the original outgoing iph, is not related to the current >> connected address. If it is possible, we have to specifically >> use the addresses in the sk instead of skb->data (i.e. iph) when >> updating the sk->sk_dst_cache. >> >> If we need to use the sk addresses (and other info) to find out a >> new dst for a connected udp socket, it is better not doing it while >> the userland is connecting to somewhere else. >> >> If the above case is impossible, we can keep using the info from iph to >> do the dst update for a connected-udp sk without taking the lock. > > I see your point, but calling __ip6_datagram_connect() seems overkill > here, we don't need to update so many things in the pmtu update context, > at least IPv4 doesn't do that either. I don't think you have to do that. > > So why just updating the dst cache (also some addr cache) here is not > enough? I think we are steadily getting closer to a version of this fix that we have some agreement on, right? Martin can you address Cong's feedback and spin another version of this series? Thanks.