[PATCH] tcp: use correct counters in CA_CWR state too

[PATCH] tcp: use correct counters in CA_CWR state too

[Ilpo Järvinen]

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As CWR is stronger than CA_Disorder state, we can miscount
SACK/Reno failure into other timeouts. Not a bad problem as
it can happen only due to ECN, FRTO detecting spurious RTO
or xmit error which are the only callers of tcp_enter_cwr.
And even then losses and RTO must still follow thereafter
to actually end up into the relevant code paths.

Compile tested.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
---
 net/ipv4/tcp_timer.c |   13 +++++++------
 1 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 74c54b3..16e591e 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -365,18 +365,19 @@ void tcp_retransmit_timer(struct sock *sk)
 	if (icsk->icsk_retransmits == 0) {
 		int mib_idx;
 
-		if (icsk->icsk_ca_state == TCP_CA_Disorder) {
-			if (tcp_is_sack(tp))
-				mib_idx = LINUX_MIB_TCPSACKFAILURES;
-			else
-				mib_idx = LINUX_MIB_TCPRENOFAILURES;
-		} else if (icsk->icsk_ca_state == TCP_CA_Recovery) {
+		if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 			if (tcp_is_sack(tp))
 				mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 			else
 				mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 		} else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 			mib_idx = LINUX_MIB_TCPLOSSFAILURES;
+		} else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
+			   tp->sacked_out) {
+			if (tcp_is_sack(tp))
+				mib_idx = LINUX_MIB_TCPSACKFAILURES;
+			else
+				mib_idx = LINUX_MIB_TCPRENOFAILURES;
 		} else {
 			mib_idx = LINUX_MIB_TCPTIMEOUTS;
 		}
-- 
1.5.6.3

Re: [PATCH] tcp: use correct counters in CA_CWR state too

[David Miller]

From: "Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi>
Date: Thu, 14 Oct 2010 14:52:09 +0300 (EEST)

> As CWR is stronger than CA_Disorder state, we can miscount
> SACK/Reno failure into other timeouts. Not a bad problem as
> it can happen only due to ECN, FRTO detecting spurious RTO
> or xmit error which are the only callers of tcp_enter_cwr.
> And even then losses and RTO must still follow thereafter
> to actually end up into the relevant code paths.
> 
> Compile tested.
> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>

Also applied to net-next-2.6, thanks.