From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cong Wang Subject: Re: [RFC PATCH net 3/4] ipv6: datagram: Update dst cache of a connected datagram sk during pmtu update Date: Mon, 4 Apr 2016 13:45:02 -0700 Message-ID: References: <1459551391-69969-1-git-send-email-kafai@fb.com> <1459551391-69969-4-git-send-email-kafai@fb.com> <20160403023349.GA57008@lichen-mbp.local.DHCP.thefacebook.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: netdev , Eric Dumazet , Wei Wang , Kernel Team To: Martin KaFai Lau Return-path: Received: from mail-yw0-f171.google.com ([209.85.161.171]:35751 "EHLO mail-yw0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932459AbcDDUpD (ORCPT ); Mon, 4 Apr 2016 16:45:03 -0400 Received: by mail-yw0-f171.google.com with SMTP id g127so267160556ywf.2 for ; Mon, 04 Apr 2016 13:45:03 -0700 (PDT) In-Reply-To: <20160403023349.GA57008@lichen-mbp.local.DHCP.thefacebook.com> Sender: netdev-owner@vger.kernel.org List-ID: 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?