From 7d227cd235c809c36c847d6a597956ad9e9d2bae Mon Sep 17 00:00:00 2001 From: Sridhar Samudrala Date: Wed, 21 May 2008 16:42:20 -0700 Subject: [PATCH] tcp: TCP connection times out if ICMP frag needed is delayed We are seeing an issue with TCP in handling an ICMP frag needed message that is received after net.ipv4.tcp_retries1 retransmits. The default value of retries1 is 3. So if the path mtu changes and ICMP frag needed is lost for the first 3 retransmits or if it gets delayed until 3 retransmits are done, TCP doesn't update MSS correctly and continues to retransmit the orginal message until it timesout after tcp_retries2 retransmits. I am seeing this issue even with the latest 2.6.25.4 kernel. In tcp_retransmit_timer(), when retransmits counter exceeds tcp_retries1 value, the dst cache entry of the socket is reset. At this time, if we receive an ICMP frag needed message, the dst entry gets updated with the new MTU, but the TCP sockets dst_cache entry remains NULL. So the next time when we try to retransmit after the ICMP frag needed is received, tcp_retransmit_skb() gets called. Here the cur_mss value is calculated at the start of the routine with a NULL sk_dst_cache. Instead we should call tcp_current_mss after the rebuild_header that caches the dst entry with the updated mtu. Also the rebuild_header should be called before tcp_fragment so that skb is fragmented if the mss goes down. Signed-off-by: Sridhar Samudrala Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index debf23581606..e399bde7813a 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1836,7 +1836,7 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); - unsigned int cur_mss = tcp_current_mss(sk, 0); + unsigned int cur_mss; int err; /* Inconslusive MTU probe */ @@ -1858,6 +1858,11 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) return -ENOMEM; } + if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk)) + return -EHOSTUNREACH; /* Routing failure or similar. */ + + cur_mss = tcp_current_mss(sk, 0); + /* If receiver has shrunk his window, and skb is out of * new window, do not retransmit it. The exception is the * case, when window is shrunk to zero. In this case @@ -1884,9 +1889,6 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) (sysctl_tcp_retrans_collapse != 0)) tcp_retrans_try_collapse(sk, skb, cur_mss); - if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk)) - return -EHOSTUNREACH; /* Routing failure or similar. */ - /* Some Solaris stacks overoptimize and ignore the FIN on a * retransmit when old data is attached. So strip it off * since it is cheap to do so and saves bytes on the network.