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On Sat, 26 Mar 2011 18:43, sec@ wrote:
Hi,
On Fri, Mar 25, 2011 at 16:40 -0400, John Baldwin wrote:
And the problem is that the code that uses 'adv' to determine if it
sound send a window update to the remote end is falsely succeeding due
to the overflow causing tcp_output() to 'goto send' but that it then
fails to send any data because it thinks the remote window is full?
On a whim I wanted to find out, how often that overflow is triggered in
normal operation, and whipped up a quick counter-sysctl.
--- sys/netinet/tcp_output.c.org 2011-01-04 19:27:00.000000000 +0100
+++ sys/netinet/tcp_output.c 2011-03-26 18:49:30.000000000 +0100
@@ -87,6 +87,11 @@
extern struct mbuf *m_copypack();
#endif
+VNET_DEFINE(int, adv_neg) = 0;
+SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, adv_neg, CTLFLAG_RD,
+ &VNET_NAME(adv_neg), 1,
+ "How many times adv got negative");
+
VNET_DEFINE(int, path_mtu_discovery) = 1;
SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
&VNET_NAME(path_mtu_discovery), 1,
@@ -573,6 +578,10 @@
long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) -
(tp->rcv_adv - tp->rcv_nxt);
+ if(min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) <
+ (tp->rcv_adv - tp->rcv_nxt))
+ adv_neg++;
+
if (adv >= (long) (2 * tp->t_maxseg))
goto send;
if (2 * adv >= (long) so->so_rcv.sb_hiwat)
I booted my main (web/shell) box with (only) this patch:
11:36PM up 3:50, 1 user, load averages: 2.29, 1.51, 0.73
net.inet.tcp.adv_neg: 2466
That's approximately once every 5 seconds. That's way more often than I
suspected.
CU,
Sec
With this patch applied with John's on a 32-bit box I can repeatedly bump
this sysctl with an SSL connection to another destination. Doesn't seem to
matter what the destination is.
curl -q https://www.changeip.com/ip.asp
It also bumps in SSL connections to other protocols too.
This behavior does not seem to be happening with non-SSL connections.
Attached is a script that I am using to monitor the sysctl here just for
reference.
L = Last value
C = Current value
D = Difference
I = Log interval
S = Seconds since last change
* = marked changed line
/bin/sh ./adv_neg_mon.sh 7 |tee -a adv_neg.log
[...]
L:41 C:41 D:0 I:7 S:7.000000e+01
L:41 C:41 D:0 I:7 S:7.700000e+01
L:41 C:43 D:2 I:7 S:8.400000e+01 *
L:43 C:88 D:45 I:7 S:7.000000e+00 *
- --
Regards,
J. Hellenthal
(0x89D8547E)
JJH48-ARIN
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#!/bin/sh
trap 'exit 1' 2
UPDATE=$1 ;: ${UPDATE:=5}
while true; do
NVAL=$(sysctl -n net.inet.tcp.adv_neg)
if [ -z "$LVAL" ]; then
LVAL=${NVAL}
fi
if [ "$NVAL" -gt "$LVAL" ]; then
echo "L:$LVAL C:$NVAL D:$((${NVAL}-${LVAL})) I:${UPDATE}
S:$(printf %e ${USECS}) *"
USECS=${UPDATE}
else
echo "L:$LVAL C:$NVAL D:$((${NVAL}-${LVAL})) I:${UPDATE}
S:$(printf %e ${USECS})"
USECS=$((${USECS}+${UPDATE}))
fi
LVAL=${NVAL}
sleep $UPDATE
done
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