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authorEric Dumazet <edumazet@google.com>2013-02-02 05:23:16 +0000
committerDavid S. Miller <davem@davemloft.net>2013-02-03 16:00:25 -0500
commit973ec449bb4f2b8c514bacbcb4d9506fc31c8ce3 (patch)
tree29d7b5de18aeff078f265f75a2a94be22254b851
parent59fa534874e6779082275d12d950e26c67c86498 (diff)
tcp: fix an infinite loop in tcp_slow_start()
Since commit 9dc274151a548 (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>
-rw-r--r--net/ipv4/tcp_cong.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 291f2ed7cc31..cdf2e707bb10 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -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);