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tcp: Stalling connections: Fix timeout calculation routine

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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
6fa12c8503 (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 <fredo@starox.org>
Signed-off-by: Damian Lukowski <damian@tvk.rwth-aachen.de>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Damian Lukowski 2009-12-07 06:06:15 +00:00 committed by David S. Miller
parent cb19054697
commit 07f29bc5bb
1 changed files with 8 additions and 2 deletions
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10
include/net/tcp.h
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@ -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)