Author: hiren
Date: Wed Jul 22 15:05:45 2015
New Revision: 285793
URL: https://svnweb.freebsd.org/changeset/base/285793
Log:
MFC r284941:
Avoid a situation where we do not set persist timer after a zero window
condition.
If you send a 0-length packet, but there is data is the socket buffer, and
neither the rexmt or persist timer is already set, then activate the persist
timer.
PR: 192599
Approved by: re (delphij)
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 Wed Jul 22 11:30:37 2015
(r285792)
+++ stable/10/sys/netinet/tcp_output.c Wed Jul 22 15:05:45 2015
(r285793)
@@ -1397,6 +1397,30 @@ timer:
tp->t_rxtshift = 0;
}
tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
+ } else if (len == 0 && so->so_snd.sb_cc &&
+ !tcp_timer_active(tp, TT_REXMT) &&
+ !tcp_timer_active(tp, TT_PERSIST)) {
+ /*
+ * Avoid a situation where we do not set persist timer
+ * after a zero window condition. For example:
+ * 1) A -> B: packet with enough data to fill the window
+ * 2) B -> A: ACK for #1 + new data (0 window
+ * advertisement)
+ * 3) A -> B: ACK for #2, 0 len packet
+ *
+ * In this case, A will not activate the persist timer,
+ * because it chose to send a packet. Unless tcp_output
+ * is called for some other reason (delayed ack timer,
+ * another input packet from B, socket syscall), A will
+ * not send zero window probes.
+ *
+ * So, if you send a 0-length packet, but there is data
+ * in the socket buffer, and neither the rexmt or
+ * persist timer is already set, then activate the
+ * persist timer.
+ */
+ tp->t_rxtshift = 0;
+ tcp_setpersist(tp);
}
} else {
/*
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