v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

[Bjørn Mork]

Hello,

I just got this message running a Debian experimental
linux-image-3.8-trunk-amd64 kernel, currently based on v3.8.5.

Peeked briefly through the commit adding the message, but I couldn't
figure out what other info you'd need so please ask if there is anything
I can dig up.

I suspect the warning could be related to problems with the iwlwifi
driver and/or access point.  The message was immediately followed  by a
few messges from iwlwifi:


Apr  8 10:58:09 nemi kernel: [152701.980799] TCP: snd_cwnd is nul, please report this bug.
Apr  8 10:58:33 nemi kernel: [152725.176151] iwlwifi 0000:03:00.0: fail to flush all tx fifo queues
Apr  8 10:58:33 nemi kernel: [152725.185713] wlan0: authenticate with 00:22:90:f9:23:a0
Apr  8 10:58:33 nemi kernel: [152725.185738] wlan0: capabilities/regulatory prevented using AP HT/VHT configuration, downgraded
Apr  8 10:58:33 nemi kernel: [152725.190150] wlan0: send auth to 00:22:90:f9:23:a0 (try 1/3)
Apr  8 10:58:33 nemi kernel: [152725.199812] wlan0: authenticated
Apr  8 10:58:33 nemi kernel: [152725.200020] iwlwifi 0000:03:00.0 wlan0: disabling HT as WMM/QoS is not supported by the AP
Apr  8 10:58:33 nemi kernel: [152725.200027] iwlwifi 0000:03:00.0 wlan0: disabling VHT as WMM/QoS is not supported by the AP
Apr  8 10:58:33 nemi kernel: [152725.204033] wlan0: associate with 00:22:90:f9:23:a0 (try 1/3)
Apr  8 10:58:33 nemi kernel: [152725.207317] wlan0: RX AssocResp from 00:22:90:f9:23:a0 (capab=0x421 status=0 aid=12)
Apr  8 10:58:33 nemi kernel: [152725.210745] wlan0: associated



Bjørn

Re: v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

[Eric Dumazet]

On Mon, 2013-04-08 at 11:06 +0200, Bjørn Mork wrote:
> Hello,
> 
> I just got this message running a Debian experimental
> linux-image-3.8-trunk-amd64 kernel, currently based on v3.8.5.
> 
> Peeked briefly through the commit adding the message, but I couldn't
> figure out what other info you'd need so please ask if there is anything
> I can dig up.
> 
> I suspect the warning could be related to problems with the iwlwifi
> driver and/or access point.  The message was immediately followed  by a
> few messges from iwlwifi:
> 
> 
> Apr  8 10:58:09 nemi kernel: [152701.980799] TCP: snd_cwnd is nul, please report this bug.
> Apr  8 10:58:33 nemi kernel: [152725.176151] iwlwifi 0000:03:00.0: fail to flush all tx fifo queues
> Apr  8 10:58:33 nemi kernel: [152725.185713] wlan0: authenticate with 00:22:90:f9:23:a0
> Apr  8 10:58:33 nemi kernel: [152725.185738] wlan0: capabilities/regulatory prevented using AP HT/VHT configuration, downgraded
> Apr  8 10:58:33 nemi kernel: [152725.190150] wlan0: send auth to 00:22:90:f9:23:a0 (try 1/3)
> Apr  8 10:58:33 nemi kernel: [152725.199812] wlan0: authenticated
> Apr  8 10:58:33 nemi kernel: [152725.200020] iwlwifi 0000:03:00.0 wlan0: disabling HT as WMM/QoS is not supported by the AP
> Apr  8 10:58:33 nemi kernel: [152725.200027] iwlwifi 0000:03:00.0 wlan0: disabling VHT as WMM/QoS is not supported by the AP
> Apr  8 10:58:33 nemi kernel: [152725.204033] wlan0: associate with 00:22:90:f9:23:a0 (try 1/3)
> Apr  8 10:58:33 nemi kernel: [152725.207317] wlan0: RX AssocResp from 00:22:90:f9:23:a0 (capab=0x421 status=0 aid=12)
> Apr  8 10:58:33 nemi kernel: [152725.210745] wlan0: associated
> 

Same issue was reported by Dave Jones on iwlwifi few days ago and I sent
following debugging patch, could you try it ?

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 4475aaf..e2e89aa 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -609,6 +609,14 @@ static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
 
 extern void tcp_set_rto(struct sock *sk);
 
+extern void tcp_snd_cwnd_bad(const struct tcp_sock *tp);
+static inline void tcp_snd_cwnd_set(struct tcp_sock *tp, u32 newval)
+{
+	if (unlikely(!newval))
+		tcp_snd_cwnd_bad(tp);
+	tp->snd_cwnd = newval;
+}
+
 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
 {
 	tp->pred_flags = htonl((tp->tcp_header_len << 26) |
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index a96f7b5..4347e22 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3300,6 +3300,33 @@ void tcp_done(struct sock *sk)
 }
 EXPORT_SYMBOL_GPL(tcp_done);
 
+void tcp_snd_cwnd_bad(const struct tcp_sock *tp)
+{
+	static bool warned = false;
+
+	if (!warned) {
+		const struct sock *sk = (struct sock *)tp;
+		const struct inet_sock *inet = inet_sk(sk);
+
+		warned = true;
+		if (sk->sk_family == AF_INET)
+			pr_err("TCP: zero snd_cwnd src:%pI4.%u dst:%pI4.%u\n",
+			       &inet->inet_saddr, ntohs(inet->inet_sport),
+			       &inet->inet_daddr, ntohs(inet->inet_dport));
+#if IS_ENABLED(CONFIG_IPV6)
+		else if (sk->sk_family == AF_INET6) {
+			const struct ipv6_pinfo *np = inet6_sk(sk);
+
+			pr_err("TCP: zero snd_cwnd src:%pI6.%u dst:%pI6.%u\n",
+			       &np->saddr, ntohs(inet->inet_sport),
+			       &np->daddr, ntohs(inet->inet_dport));
+		}
+#endif
+		WARN_ON_ONCE(1);
+	}
+}
+EXPORT_SYMBOL(tcp_snd_cwnd_bad);
+
 extern struct tcp_congestion_ops tcp_reno;
 
 static __initdata unsigned long thash_entries;
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 019c238..6ddd167 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -327,7 +327,7 @@ void tcp_slow_start(struct tcp_sock *tp)
 		tp->snd_cwnd_cnt -= snd_cwnd;
 		delta++;
 	}
-	tp->snd_cwnd = min(snd_cwnd + delta, tp->snd_cwnd_clamp);
+	tcp_snd_cwnd_set(tp, min(snd_cwnd + delta, tp->snd_cwnd_clamp));
 }
 EXPORT_SYMBOL_GPL(tcp_slow_start);
 
diff --git a/net/ipv4/tcp_hybla.c b/net/ipv4/tcp_hybla.c
index 57bdd17..d236b70 100644
--- a/net/ipv4/tcp_hybla.c
+++ b/net/ipv4/tcp_hybla.c
@@ -60,7 +60,7 @@ static void hybla_init(struct sock *sk)
 
 	/* set minimum rtt as this is the 1st ever seen */
 	ca->minrtt = tp->srtt;
-	tp->snd_cwnd = ca->rho;
+	tcp_snd_cwnd_set(tp, ca->rho);
 }
 
 static void hybla_state(struct sock *sk, u8 ca_state)
@@ -157,9 +157,9 @@ static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 	}
 	/* clamp down slowstart cwnd to ssthresh value. */
 	if (is_slowstart)
-		tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
+		tcp_snd_cwnd_set(tp, min(tp->snd_cwnd, tp->snd_ssthresh));
 
-	tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
+	tcp_snd_cwnd_set(tp, min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp));
 }
 
 static struct tcp_congestion_ops tcp_hybla __read_mostly = {
diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c
index 834857f..71135e3 100644
--- a/net/ipv4/tcp_illinois.c
+++ b/net/ipv4/tcp_illinois.c
@@ -284,8 +284,9 @@ static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 		*/
 		delta = (tp->snd_cwnd_cnt * ca->alpha) >> ALPHA_SHIFT;
 		if (delta >= tp->snd_cwnd) {
-			tp->snd_cwnd = min(tp->snd_cwnd + delta / tp->snd_cwnd,
-					   (u32) tp->snd_cwnd_clamp);
+			tcp_snd_cwnd_set(tp,
+					 min(tp->snd_cwnd + delta / tp->snd_cwnd,
+					     (u32) tp->snd_cwnd_clamp));
 			tp->snd_cwnd_cnt = 0;
 		}
 	}
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 6d9ca35..b972577 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2259,8 +2259,8 @@ static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
  */
 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
 {
-	tp->snd_cwnd = min(tp->snd_cwnd,
-			   tcp_packets_in_flight(tp) + tcp_max_burst(tp));
+	tcp_snd_cwnd_set(tp, min(tp->snd_cwnd,
+				 tcp_packets_in_flight(tp) + tcp_max_burst(tp)));
 	tp->snd_cwnd_stamp = tcp_time_stamp;
 }
 
@@ -2312,18 +2312,20 @@ static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh)
 
 	if (tp->prior_ssthresh) {
 		const struct inet_connection_sock *icsk = inet_csk(sk);
+		u32 newval;
 
 		if (icsk->icsk_ca_ops->undo_cwnd)
-			tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
+			newval = icsk->icsk_ca_ops->undo_cwnd(sk);
 		else
-			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
+			newval = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
+		tcp_snd_cwnd_set(tp, newval);
 
 		if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) {
 			tp->snd_ssthresh = tp->prior_ssthresh;
 			TCP_ECN_withdraw_cwr(tp);
 		}
 	} else {
-		tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
+		tcp_snd_cwnd_set(tp, max(tp->snd_cwnd, tp->snd_ssthresh));
 	}
 	tp->snd_cwnd_stamp = tcp_time_stamp;
 }
@@ -2512,7 +2514,7 @@ static void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked,
 	}
 
 	sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
-	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
+	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt);
 }
 
 static inline void tcp_end_cwnd_reduction(struct sock *sk)
@@ -2522,7 +2524,7 @@ static inline void tcp_end_cwnd_reduction(struct sock *sk)
 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
 	    (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
-		tp->snd_cwnd = tp->snd_ssthresh;
+		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
 		tp->snd_cwnd_stamp = tcp_time_stamp;
 	}
 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
@@ -2591,9 +2593,9 @@ static void tcp_mtup_probe_success(struct sock *sk)
 
 	/* FIXME: breaks with very large cwnd */
 	tp->prior_ssthresh = tcp_current_ssthresh(sk);
-	tp->snd_cwnd = tp->snd_cwnd *
-		       tcp_mss_to_mtu(sk, tp->mss_cache) /
-		       icsk->icsk_mtup.probe_size;
+	tcp_snd_cwnd_set(tp, tp->snd_cwnd *
+			     tcp_mss_to_mtu(sk, tp->mss_cache) /
+			     icsk->icsk_mtup.probe_size);
 	tp->snd_cwnd_cnt = 0;
 	tp->snd_cwnd_stamp = tcp_time_stamp;
 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
@@ -4665,7 +4667,7 @@ void tcp_cwnd_application_limited(struct sock *sk)
 		u32 win_used = max(tp->snd_cwnd_used, init_win);
 		if (win_used < tp->snd_cwnd) {
 			tp->snd_ssthresh = tcp_current_ssthresh(sk);
-			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
+			tcp_snd_cwnd_set(tp, (tp->snd_cwnd + win_used) >> 1);
 		}
 		tp->snd_cwnd_used = 0;
 	}
diff --git a/net/ipv4/tcp_lp.c b/net/ipv4/tcp_lp.c
index 72f7218..09bf418 100644
--- a/net/ipv4/tcp_lp.c
+++ b/net/ipv4/tcp_lp.c
@@ -307,7 +307,7 @@ static void tcp_lp_pkts_acked(struct sock *sk, u32 num_acked, s32 rtt_us)
 	/* happened after inference
 	 * cut snd_cwnd into half */
 	else
-		tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U);
+		tcp_snd_cwnd_set(tp, max(tp->snd_cwnd >> 1U, 1U));
 
 	/* record this drop time */
 	lp->last_drop = tcp_time_stamp;
diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index f696d7c..d5a6608 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -526,7 +526,7 @@ reset:
 	if (tp->total_retrans > 1)
 		tp->snd_cwnd = 1;
 	else
-		tp->snd_cwnd = tcp_init_cwnd(tp, dst);
+		tcp_snd_cwnd_set(tp, tcp_init_cwnd(tp, dst));
 	tp->snd_cwnd_stamp = tcp_time_stamp;
 }
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index af354c98..2b80083 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -148,7 +148,7 @@ static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
 
 	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
 		cwnd >>= 1;
-	tp->snd_cwnd = max(cwnd, restart_cwnd);
+	tcp_snd_cwnd_set(tp, max(cwnd, restart_cwnd));
 	tp->snd_cwnd_stamp = tcp_time_stamp;
 	tp->snd_cwnd_used = 0;
 }
diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c
index 80fa2bf..a270cf9 100644
--- a/net/ipv4/tcp_vegas.c
+++ b/net/ipv4/tcp_vegas.c
@@ -238,7 +238,8 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 				 * truncation robs us of full link
 				 * utilization.
 				 */
-				tp->snd_cwnd = min(tp->snd_cwnd, (u32)target_cwnd+1);
+				tcp_snd_cwnd_set(tp, min(tp->snd_cwnd,
+							 (u32)target_cwnd + 1));
 				tp->snd_ssthresh = tcp_vegas_ssthresh(tp);
 
 			} else if (tp->snd_cwnd <= tp->snd_ssthresh) {
@@ -272,7 +273,7 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 			if (tp->snd_cwnd < 2)
 				tp->snd_cwnd = 2;
 			else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
-				tp->snd_cwnd = tp->snd_cwnd_clamp;
+				tcp_snd_cwnd_set(tp, tp->snd_cwnd_clamp);
 
 			tp->snd_ssthresh = tcp_current_ssthresh(sk);
 		}
diff --git a/net/ipv4/tcp_veno.c b/net/ipv4/tcp_veno.c
index ac43cd7..d1fa5c1 100644
--- a/net/ipv4/tcp_veno.c
+++ b/net/ipv4/tcp_veno.c
@@ -180,7 +180,7 @@ static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 		if (tp->snd_cwnd < 2)
 			tp->snd_cwnd = 2;
 		else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
-			tp->snd_cwnd = tp->snd_cwnd_clamp;
+			tcp_snd_cwnd_set(tp, tp->snd_cwnd_clamp);
 	}
 	/* Wipe the slate clean for the next rtt. */
 	/* veno->cntrtt = 0; */
diff --git a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c
index 76a1e23..060fbb5 100644
--- a/net/ipv4/tcp_westwood.c
+++ b/net/ipv4/tcp_westwood.c
@@ -233,7 +233,8 @@ static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
 		break;
 
 	case CA_EVENT_COMPLETE_CWR:
-		tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+		tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
 		break;
 
 	case CA_EVENT_LOSS:
diff --git a/net/ipv4/tcp_yeah.c b/net/ipv4/tcp_yeah.c
index 05c3b6f..3ad1dbb 100644
--- a/net/ipv4/tcp_yeah.c
+++ b/net/ipv4/tcp_yeah.c
@@ -161,11 +161,9 @@ static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 				    tp->snd_cwnd > yeah->reno_count) {
 					u32 reduction = min(queue / TCP_YEAH_GAMMA ,
 							    tp->snd_cwnd >> TCP_YEAH_EPSILON);
+					u32 tmp = tp->snd_cwnd - reduction;
 
-					tp->snd_cwnd -= reduction;
-
-					tp->snd_cwnd = max(tp->snd_cwnd,
-							   yeah->reno_count);
+					tcp_snd_cwnd_set(tp, max(tmp, yeah->reno_count));
 
 					tp->snd_ssthresh = tp->snd_cwnd;
 				}

Re: v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

[Bjørn Mork]

Eric Dumazet <eric.dumazet@gmail.com> writes:
> On Mon, 2013-04-08 at 11:06 +0200, Bjørn Mork wrote:
>
>> Apr  8 10:58:09 nemi kernel: [152701.980799] TCP: snd_cwnd is nul, please report this bug.
>> Apr  8 10:58:33 nemi kernel: [152725.176151] iwlwifi 0000:03:00.0: fail to flush all tx fifo queues
>> Apr  8 10:58:33 nemi kernel: [152725.185713] wlan0: authenticate with 00:22:90:f9:23:a0
>> Apr  8 10:58:33 nemi kernel: [152725.185738] wlan0: capabilities/regulatory prevented using AP HT/VHT configuration, downgraded
>> Apr  8 10:58:33 nemi kernel: [152725.190150] wlan0: send auth to 00:22:90:f9:23:a0 (try 1/3)
>> Apr  8 10:58:33 nemi kernel: [152725.199812] wlan0: authenticated
>> Apr  8 10:58:33 nemi kernel: [152725.200020] iwlwifi 0000:03:00.0 wlan0: disabling HT as WMM/QoS is not supported by the AP
>> Apr  8 10:58:33 nemi kernel: [152725.200027] iwlwifi 0000:03:00.0 wlan0: disabling VHT as WMM/QoS is not supported by the AP
>> Apr  8 10:58:33 nemi kernel: [152725.204033] wlan0: associate with 00:22:90:f9:23:a0 (try 1/3)
>> Apr  8 10:58:33 nemi kernel: [152725.207317] wlan0: RX AssocResp from 00:22:90:f9:23:a0 (capab=0x421 status=0 aid=12)
>> Apr  8 10:58:33 nemi kernel: [152725.210745] wlan0: associated
>> 
>
> Same issue was reported by Dave Jones on iwlwifi few days ago and I sent
> following debugging patch, could you try it ?

Will do. The patch only applied on top of net-next, so I assume that's
what you want me to test it on?

I looked through my logs and the 'fail to flush all tx fifo queues'
warning from iwlwifi appears very infrequent.  The last time before
today was March 18th...  Also accompanied by your warning.  That's the
only two times I've seen that one. And I've been running v3.8-rc7 (where
you introduced the warning) or newer since Feb 8th.

So don't hold your breath.  This may take a few weeks to trigger again.


Bjørn

Re: v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

[Eric Dumazet]

On Mon, 2013-04-08 at 17:14 +0200, Bjørn Mork wrote:
> Eric Dumazet <eric.dumazet@gmail.com> writes:
> > On Mon, 2013-04-08 at 11:06 +0200, Bjørn Mork wrote:
> >
> >> Apr  8 10:58:09 nemi kernel: [152701.980799] TCP: snd_cwnd is nul, please report this bug.
> >> Apr  8 10:58:33 nemi kernel: [152725.176151] iwlwifi 0000:03:00.0: fail to flush all tx fifo queues
> >> Apr  8 10:58:33 nemi kernel: [152725.185713] wlan0: authenticate with 00:22:90:f9:23:a0
> >> Apr  8 10:58:33 nemi kernel: [152725.185738] wlan0: capabilities/regulatory prevented using AP HT/VHT configuration, downgraded
> >> Apr  8 10:58:33 nemi kernel: [152725.190150] wlan0: send auth to 00:22:90:f9:23:a0 (try 1/3)
> >> Apr  8 10:58:33 nemi kernel: [152725.199812] wlan0: authenticated
> >> Apr  8 10:58:33 nemi kernel: [152725.200020] iwlwifi 0000:03:00.0 wlan0: disabling HT as WMM/QoS is not supported by the AP
> >> Apr  8 10:58:33 nemi kernel: [152725.200027] iwlwifi 0000:03:00.0 wlan0: disabling VHT as WMM/QoS is not supported by the AP
> >> Apr  8 10:58:33 nemi kernel: [152725.204033] wlan0: associate with 00:22:90:f9:23:a0 (try 1/3)
> >> Apr  8 10:58:33 nemi kernel: [152725.207317] wlan0: RX AssocResp from 00:22:90:f9:23:a0 (capab=0x421 status=0 aid=12)
> >> Apr  8 10:58:33 nemi kernel: [152725.210745] wlan0: associated
> >> 
> >
> > Same issue was reported by Dave Jones on iwlwifi few days ago and I sent
> > following debugging patch, could you try it ?
> 
> Will do. The patch only applied on top of net-next, so I assume that's
> what you want me to test it on?
> 
> I looked through my logs and the 'fail to flush all tx fifo queues'
> warning from iwlwifi appears very infrequent.  The last time before
> today was March 18th...  Also accompanied by your warning.  That's the
> only two times I've seen that one. And I've been running v3.8-rc7 (where
> you introduced the warning) or newer since Feb 8th.
> 
> So don't hold your breath.  This may take a few weeks to trigger again.
> 

I believe patch applies (with some fuzz) on Linus tree, and maybe on 3.8
too.

Re: v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

[Bjørn Mork]

Eric Dumazet <eric.dumazet@gmail.com> writes:

> I believe patch applies (with some fuzz) on Linus tree, and maybe on 3.8
> too.

Probably just a minor context issue, but it failed like this on v3.9-rc6
(as well as 'net' and v3.8.6):

     Applying: v3.8.5: "TCP: snd_cwnd is nul, please report this bug."
     error: patch failed: net/ipv4/tcp_westwood.c:233
     error: net/ipv4/tcp_westwood.c: patch does not apply


I'll just run todays net-next with this on top.  No problem.



Bjørn

Re: v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

[Bjørn Mork]

Eric Dumazet <eric.dumazet@gmail.com> writes:
> On Mon, 2013-04-08 at 17:14 +0200, Bjørn Mork wrote:
>> Eric Dumazet <eric.dumazet@gmail.com> writes:
>> > On Mon, 2013-04-08 at 11:06 +0200, Bjørn Mork wrote:
>> >
>> >> Apr  8 10:58:09 nemi kernel: [152701.980799] TCP: snd_cwnd is nul, please report this bug.
>> >> Apr  8 10:58:33 nemi kernel: [152725.176151] iwlwifi 0000:03:00.0: fail to flush all tx fifo queues
>> >> Apr  8 10:58:33 nemi kernel: [152725.185713] wlan0: authenticate with 00:22:90:f9:23:a0
>> >> Apr  8 10:58:33 nemi kernel: [152725.185738] wlan0: capabilities/regulatory prevented using AP HT/VHT configuration, downgraded
>> >> Apr  8 10:58:33 nemi kernel: [152725.190150] wlan0: send auth to 00:22:90:f9:23:a0 (try 1/3)
>> >> Apr  8 10:58:33 nemi kernel: [152725.199812] wlan0: authenticated
>> >> Apr  8 10:58:33 nemi kernel: [152725.200020] iwlwifi 0000:03:00.0 wlan0: disabling HT as WMM/QoS is not supported by the AP
>> >> Apr  8 10:58:33 nemi kernel: [152725.200027] iwlwifi 0000:03:00.0 wlan0: disabling VHT as WMM/QoS is not supported by the AP
>> >> Apr  8 10:58:33 nemi kernel: [152725.204033] wlan0: associate with 00:22:90:f9:23:a0 (try 1/3)
>> >> Apr  8 10:58:33 nemi kernel: [152725.207317] wlan0: RX AssocResp from 00:22:90:f9:23:a0 (capab=0x421 status=0 aid=12)
>> >> Apr  8 10:58:33 nemi kernel: [152725.210745] wlan0: associated
>> >> 
>> >
>> > Same issue was reported by Dave Jones on iwlwifi few days ago and I sent
>> > following debugging patch, could you try it ?
>> 
>> Will do. The patch only applied on top of net-next, so I assume that's
>> what you want me to test it on?
>> 
>> I looked through my logs and the 'fail to flush all tx fifo queues'
>> warning from iwlwifi appears very infrequent.  The last time before
>> today was March 18th...  Also accompanied by your warning.  That's the
>> only two times I've seen that one. And I've been running v3.8-rc7 (where
>> you introduced the warning) or newer since Feb 8th.
>> 
>> So don't hold your breath.  This may take a few weeks to trigger again.
>
> I believe patch applies (with some fuzz) on Linus tree, and maybe on 3.8
> too.

Just FYI, in case you wondered what happened here...

I've been running with the debug patch since you sent it to me, and
still is.  But the warning has not yet reappeared.

I'll continue using the patch for a while, but will eventually drop it
if the warning cannot be reproduced in another couple of weeks time.
There have been a few fixes to iwlwifi in the meantime, and I do not
rule out the possibility that some of these removed the triggering
event.


Thanks,
Bjørn

Re: v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

[Eric Dumazet]

On Sun, 2013-06-02 at 12:19 +0200, Bjørn Mork wrote:

> Just FYI, in case you wondered what happened here...
> 
> I've been running with the debug patch since you sent it to me, and
> still is.  But the warning has not yet reappeared.
> 
> I'll continue using the patch for a while, but will eventually drop it
> if the warning cannot be reproduced in another couple of weeks time.
> There have been a few fixes to iwlwifi in the meantime, and I do not
> rule out the possibility that some of these removed the triggering
> event.
> 

What exact tree are you running ?

F-RTO code was replaced by Yuching Cheng, and it might very well have
solved these issues.

commit e33099f96d99c391b3325caa9c44258de04aae86 
("tcp: implement RFC5682 F-RTO")

commit ab42d9ee3d215ab74a49818ffc53771a88ce7ddf
("tcp: refactor CA_Loss state processing")

commit 9b44190dc114c1720b34975b5bfc65aece112ced
("tcp: refactor F-RTO")

Thanks

Re: v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

[Eric Dumazet]

On Sun, 2013-06-02 at 07:22 -0700, Eric Dumazet wrote:
> F-RTO code was replaced by Yuching Cheng, and it might very well have
> solved these issues.

Sorry for the misspell, its Yuchung, of course.

Re: v3.8.5: "TCP: snd_cwnd is nul, please report this bug."

[Bjørn Mork]

Eric Dumazet <eric.dumazet@gmail.com> writes:
> On Sun, 2013-06-02 at 12:19 +0200, Bjørn Mork wrote:
>
>> Just FYI, in case you wondered what happened here...
>> 
>> I've been running with the debug patch since you sent it to me, and
>> still is.  But the warning has not yet reappeared.
>> 
>> I'll continue using the patch for a while, but will eventually drop it
>> if the warning cannot be reproduced in another couple of weeks time.
>> There have been a few fixes to iwlwifi in the meantime, and I do not
>> rule out the possibility that some of these removed the triggering
>> event.
>> 
>
> What exact tree are you running ?

I am currently testing the mainline v3.10-rcX releases.  I.e. v3.10-rc4
right now.

> F-RTO code was replaced by Yuching Cheng, and it might very well have
> solved these issues.
>
> commit e33099f96d99c391b3325caa9c44258de04aae86 
> ("tcp: implement RFC5682 F-RTO")
>
> commit ab42d9ee3d215ab74a49818ffc53771a88ce7ddf
> ("tcp: refactor CA_Loss state processing")
>
> commit 9b44190dc114c1720b34975b5bfc65aece112ced
> ("tcp: refactor F-RTO")

Right.

I'll assume the problem is fixed then.  Will drop the debug patch for
now, but resurrect it and let you know if I ever see the warning again.


Bjørn