svn commit: r302132 - stable/10/sys/netinet
Sepherosa Ziehau
sephe at FreeBSD.org
Thu Jun 23 08:38:02 UTC 2016
Author: sephe
Date: Thu Jun 23 08:38:01 2016
New Revision: 302132
URL: https://svnweb.freebsd.org/changeset/base/302132
Log:
MFC 300981
tcp: Don't prematurely drop receiving-only connections
If the connection was persistent and receiving-only, several (12)
sporadic device insufficient buffers would cause the connection be
dropped prematurely:
Upon ENOBUFS in tcp_output() for an ACK, retransmission timer is
started. No one will stop this retransmission timer for receiving-
only connection, so the retransmission timer promises to expire and
t_rxtshift is promised to be increased. And t_rxtshift will not be
reset to 0, since no RTT measurement will be done for receiving-only
connection. If this receiving-only connection lived long enough
(e.g. >350sec, given the RTO starts from 200ms), and it suffered 12
sporadic device insufficient buffers, i.e. t_rxtshift >= 12, this
receiving-only connection would be dropped prematurely by the
retransmission timer.
We now assert that for data segments, SYNs or FINs either rexmit or
persist timer was wired upon ENOBUFS. And don't set rexmit timer
for other cases, i.e. ENOBUFS upon ACKs.
Discussed with: lstewart, hiren, jtl, Mike Karels
MFC after: 3 weeks
Sponsored by: Microsoft OSTC
Differential Revision: https://reviews.freebsd.org/D5872
Modified:
stable/10/sys/netinet/tcp_output.c
Directory Properties:
stable/10/ (props changed)
Modified: stable/10/sys/netinet/tcp_output.c
==============================================================================
--- stable/10/sys/netinet/tcp_output.c Thu Jun 23 08:28:13 2016 (r302131)
+++ stable/10/sys/netinet/tcp_output.c Thu Jun 23 08:38:01 2016 (r302132)
@@ -127,6 +127,16 @@ SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO,
&VNET_NAME(tcp_autosndbuf_max), 0,
"Max size of automatic send buffer");
+/*
+ * Make sure that either retransmit or persist timer is set for SYN, FIN and
+ * non-ACK.
+ */
+#define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags) \
+ KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
+ tcp_timer_active((tp), TT_REXMT) || \
+ tcp_timer_active((tp), TT_PERSIST), \
+ ("neither rexmt nor persist timer is set"))
+
static void inline hhook_run_tcp_est_out(struct tcpcb *tp,
struct tcphdr *th, struct tcpopt *to,
long len, int tso);
@@ -1531,9 +1541,7 @@ timer:
tp->t_softerror = error;
return (error);
case ENOBUFS:
- if (!tcp_timer_active(tp, TT_REXMT) &&
- !tcp_timer_active(tp, TT_PERSIST))
- tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
+ TCP_XMIT_TIMER_ASSERT(tp, len, flags);
tp->snd_cwnd = tp->t_maxseg;
return (0);
case EMSGSIZE:
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