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tcp/lro: If timestamps mismatch or it's a FIN, force flush.

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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
This commit is contained in:
Sepherosa Ziehau 2016-08-05 09:08:00 +00:00
parent f87a304c8b
commit b9ec6f0b02
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=303766
1 changed files with 32 additions and 4 deletions
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36
sys/netinet/tcp_lro.c
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@ -603,6 +603,7 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
int error, ip_len, l;
uint16_t eh_type, tcp_data_len;
struct lro_head *bucket;
int force_flush = 0;
/* We expect a contiguous header [eh, ip, tcp]. */
@ -669,8 +670,15 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
* 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? */
@ -686,8 +694,13 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
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)
@ -754,6 +767,13 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
#endif
}
if (force_flush) {
/* Timestamps mismatch; this is a FIN, etc */
tcp_lro_active_remove(le);
tcp_lro_flush(lc, le);
return (TCP_LRO_CANNOT);
}
/* Flush now if appending will result in overflow. */
if (le->p_len > (lc->lro_length_lim - tcp_data_len)) {
tcp_lro_active_remove(le);
@ -830,6 +850,14 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
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 (LIST_EMPTY(&lc->lro_free))
return (TCP_LRO_NO_ENTRIES);