From 07f29bc5bbae4e53e982ab956fed7207990a7786 Mon Sep 17 00:00:00 2001 From: Damian Lukowski Date: Mon, 7 Dec 2009 06:06:15 +0000 Subject: [PATCH] tcp: Stalling connections: Fix timeout calculation routine MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This patch fixes a problem in the TCP connection timeout calculation. Currently, timeout decisions are made on the basis of the current tcp_time_stamp and retrans_stamp, which is usually set at the first retransmission. However, if the retransmission fails in tcp_retransmit_skb(), retrans_stamp is not updated and remains zero. This leads to wrong decisions in retransmits_timed_out() if tcp_time_stamp is larger than the specified timeout, which is very likely. In this case, the TCP connection dies after the first attempted (and unsuccessful) retransmission. With this patch, tcp_skb_cb->when is used instead, when retrans_stamp is not available. This bug has been introduced together with retransmits_timed_out() in 2.6.32, as the number of retransmissions has been used for timeout decisions before. The corresponding commit was 6fa12c85031485dff38ce550c24f10da23b0adaa (Revert Backoff [v3]: Calculate TCP's connection close threshold as a time value.). Thanks to Ilpo Järvinen for code suggestions and Frederic Leroy for testing. Reported-by: Frederic Leroy Signed-off-by: Damian Lukowski Acked-by: Ilpo Järvinen Signed-off-by: David S. Miller --- include/net/tcp.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index e2d2ca2509be..e54bd85d9d40 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1265,14 +1265,20 @@ static inline struct sk_buff *tcp_write_queue_prev(struct sock *sk, struct sk_bu * TCP connection after "boundary" unsucessful, exponentially backed-off * retransmissions with an initial RTO of TCP_RTO_MIN. */ -static inline bool retransmits_timed_out(const struct sock *sk, +static inline bool retransmits_timed_out(struct sock *sk, unsigned int boundary) { unsigned int timeout, linear_backoff_thresh; + unsigned int start_ts; if (!inet_csk(sk)->icsk_retransmits) return false; + if (unlikely(!tcp_sk(sk)->retrans_stamp)) + start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when; + else + start_ts = tcp_sk(sk)->retrans_stamp; + linear_backoff_thresh = ilog2(TCP_RTO_MAX/TCP_RTO_MIN); if (boundary <= linear_backoff_thresh) @@ -1281,7 +1287,7 @@ static inline bool retransmits_timed_out(const struct sock *sk, timeout = ((2 << linear_backoff_thresh) - 1) * TCP_RTO_MIN + (boundary - linear_backoff_thresh) * TCP_RTO_MAX; - return (tcp_time_stamp - tcp_sk(sk)->retrans_stamp) >= timeout; + return (tcp_time_stamp - start_ts) >= timeout; } static inline struct sk_buff *tcp_send_head(struct sock *sk) -- GitLab