Author: sephe
Date: Fri Aug 26 06:19:12 2016
New Revision: 304836
URL: https://svnweb.freebsd.org/changeset/base/304836
Log:
MFC 303766
tcp/lro: If timestamps mismatch or it's a FIN, force flush.
This keeps the segments/ACK/FIN delivery order.
Before this patch, it was observed: if A sent FIN immediately after
an ACK, B would deliver FIN first to the TCP stack, then the ACK.
This out-of-order delivery causes one unnecessary ACK sent from B.
Reviewed by: gallatin, hps
Obtained from: rrs, gallatin
Sponsored by: Netflix (rrs, gallatin), Microsoft (sephe)
Differential Revision: https://reviews.freebsd.org/D7415
Modified:
stable/10/sys/netinet/tcp_lro.c
Directory Properties:
stable/10/ (props changed)
Modified: stable/10/sys/netinet/tcp_lro.c
==============================================================================
--- stable/10/sys/netinet/tcp_lro.c Fri Aug 26 05:37:44 2016
(r304835)
+++ stable/10/sys/netinet/tcp_lro.c Fri Aug 26 06:19:12 2016
(r304836)
@@ -382,6 +382,7 @@ tcp_lro_rx(struct lro_ctrl *lc, struct m
tcp_seq seq;
int error, ip_len, l;
uint16_t eh_type, tcp_data_len;
+ int force_flush = 0;
/* We expect a contiguous header [eh, ip, tcp]. */
@@ -448,8 +449,15 @@ tcp_lro_rx(struct lro_ctrl *lc, struct m
* Check TCP header constraints.
*/
/* Ensure no bits set besides ACK or PSH. */
- if ((th->th_flags & ~(TH_ACK | TH_PUSH)) != 0)
- return (TCP_LRO_CANNOT);
+ if ((th->th_flags & ~(TH_ACK | TH_PUSH)) != 0) {
+ if (th->th_flags & TH_SYN)
+ return (TCP_LRO_CANNOT);
+ /*
+ * Make sure that previously seen segements/ACKs are delivered
+ * before this segement, e.g. FIN.
+ */
+ force_flush = 1;
+ }
/* XXX-BZ We lose a ACK|PUSH flag concatenating multiple segments. */
/* XXX-BZ Ideally we'd flush on PUSH? */
@@ -465,8 +473,13 @@ tcp_lro_rx(struct lro_ctrl *lc, struct m
ts_ptr = (uint32_t *)(th + 1);
if (l != 0 && (__predict_false(l != TCPOLEN_TSTAMP_APPA) ||
(*ts_ptr != ntohl(TCPOPT_NOP<<24|TCPOPT_NOP<<16|
- TCPOPT_TIMESTAMP<<8|TCPOLEN_TIMESTAMP))))
- return (TCP_LRO_CANNOT);
+ TCPOPT_TIMESTAMP<<8|TCPOLEN_TIMESTAMP)))) {
+ /*
+ * Make sure that previously seen segements/ACKs are delivered
+ * before this segement.
+ */
+ force_flush = 1;
+ }
/* If the driver did not pass in the checksum, set it now. */
if (csum == 0x0000)
@@ -500,6 +513,13 @@ tcp_lro_rx(struct lro_ctrl *lc, struct m
#endif
}
+ if (force_flush) {
+ /* Timestamps mismatch; this is a FIN, etc */
+ SLIST_REMOVE(&lc->lro_active, le, lro_entry, next);
+ tcp_lro_flush(lc, le);
+ return (TCP_LRO_CANNOT);
+ }
+
/* Flush now if appending will result in overflow. */
if (le->p_len > (65535 - tcp_data_len)) {
SLIST_REMOVE(&lc->lro_active, le, lro_entry, next);
@@ -568,6 +588,14 @@ tcp_lro_rx(struct lro_ctrl *lc, struct m
return (0);
}
+ if (force_flush) {
+ /*
+ * Nothing to flush, but this segment can not be further
+ * aggregated/delayed.
+ */
+ return (TCP_LRO_CANNOT);
+ }
+
/* Try to find an empty slot. */
if (SLIST_EMPTY(&lc->lro_free))
return (TCP_LRO_NO_ENTRIES);
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