netdev - Re: Change in IPv4 TCP reset behavior after kernel upgrade

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Message-ID: <1386200221.30495.143.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 04 Dec 2013 15:37:01 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Fiedler Roman <Roman.Fiedler@....ac.at>,
	Neal Cardwell <ncardwell@...gle.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Change in IPv4 TCP reset behavior after kernel upgrade

On Wed, 2013-12-04 at 23:02 +0100, Hannes Frederic Sowa wrote:

> Oh yes, actually looking at the code we definitely run into __ip_select_ident
> and generate an inetpeer and use the derived ipid from that.
> 
> Roman, I would be very interested why you only experienced that with
> 3.10.21, could you share the specific vserver patch?

BTW I think we might have an opportunity to respect no_pmtu_disc sysctl
as in :

(ie have DF bit set or unset for RST packets, and ACK packets sent on behalf
of TIMEWAIT sockets)

Still we use a non 0 id for these packets.

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 9124027..a1e05a9 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1473,7 +1473,6 @@ static DEFINE_PER_CPU(struct inet_sock, unicast_sock) = {
                .sk_allocation  = GFP_ATOMIC,
                .sk_flags       = (1UL << SOCK_USE_WRITE_QUEUE),
        },
-       .pmtudisc       = IP_PMTUDISC_WANT,
        .uc_ttl         = -1,
 };
 
@@ -1519,6 +1518,7 @@ void ip_send_unicast_reply(struct net *net, struct sk_buff *skb, __be32 daddr,
        inet = &get_cpu_var(unicast_sock);
 
        inet->tos = arg->tos;
+       inet->pmtudisc = ipv4_config.no_pmtu_disc ? IP_PMTUDISC_DONT : IP_PMTUDISC_WANT;
        sk = &inet->sk;
        sk->sk_priority = skb->priority;
        sk->sk_protocol = ip_hdr(skb)->protocol;


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