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tcp: fix an infinite loop in tcp_slow_start()

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Since commit 9dc274151a (tcp: fix ABC in tcp_slow_start()),
a nul snd_cwnd triggers an infinite loop in tcp_slow_start()

Avoid this infinite loop and log a one time error for further
analysis. FRTO code is suspected to cause this bug.

Reported-by: Pasi Kärkkäinen <pasik@iki.fi>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2013-02-02 05:23:16 +00:00 committed by David S. Miller
parent 59fa534874
commit 973ec449bb
1 changed files with 10 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
net/ipv4/tcp_cong.c
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@ -310,6 +310,12 @@ void tcp_slow_start(struct tcp_sock *tp)
{
int cnt; /* increase in packets */
unsigned int delta = 0;
u32 snd_cwnd = tp->snd_cwnd;
if (unlikely(!snd_cwnd)) {
pr_err_once("snd_cwnd is nul, please report this bug.\n");
snd_cwnd = 1U;
}
/* RFC3465: ABC Slow start
* Increase only after a full MSS of bytes is acked
@ -324,7 +330,7 @@ void tcp_slow_start(struct tcp_sock *tp)
if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
else
cnt = tp->snd_cwnd; /* exponential increase */
cnt = snd_cwnd; /* exponential increase */
/* RFC3465: ABC
* We MAY increase by 2 if discovered delayed ack
@ -334,11 +340,11 @@ void tcp_slow_start(struct tcp_sock *tp)
tp->bytes_acked = 0;
tp->snd_cwnd_cnt += cnt;
while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
tp->snd_cwnd_cnt -= tp->snd_cwnd;
while (tp->snd_cwnd_cnt >= snd_cwnd) {
tp->snd_cwnd_cnt -= snd_cwnd;
delta++;
}
tp->snd_cwnd = min(tp->snd_cwnd + delta, tp->snd_cwnd_clamp);
tp->snd_cwnd = min(snd_cwnd + delta, tp->snd_cwnd_clamp);
}
EXPORT_SYMBOL_GPL(tcp_slow_start);