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
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=303766
@ -603,6 +603,7 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
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int error, ip_len, l;
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uint16_t eh_type, tcp_data_len;
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struct lro_head *bucket;
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int force_flush = 0;
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/* We expect a contiguous header [eh, ip, tcp]. */
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@ -669,8 +670,15 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
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* Check TCP header constraints.
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*/
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/* Ensure no bits set besides ACK or PSH. */
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if ((th->th_flags & ~(TH_ACK | TH_PUSH)) != 0)
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return (TCP_LRO_CANNOT);
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if ((th->th_flags & ~(TH_ACK | TH_PUSH)) != 0) {
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if (th->th_flags & TH_SYN)
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return (TCP_LRO_CANNOT);
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/*
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* Make sure that previously seen segements/ACKs are delivered
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* before this segement, e.g. FIN.
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*/
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force_flush = 1;
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}
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/* XXX-BZ We lose a ACK|PUSH flag concatenating multiple segments. */
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/* XXX-BZ Ideally we'd flush on PUSH? */
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@ -686,8 +694,13 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
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ts_ptr = (uint32_t *)(th + 1);
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if (l != 0 && (__predict_false(l != TCPOLEN_TSTAMP_APPA) ||
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(*ts_ptr != ntohl(TCPOPT_NOP<<24|TCPOPT_NOP<<16|
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TCPOPT_TIMESTAMP<<8|TCPOLEN_TIMESTAMP))))
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return (TCP_LRO_CANNOT);
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TCPOPT_TIMESTAMP<<8|TCPOLEN_TIMESTAMP)))) {
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/*
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* Make sure that previously seen segements/ACKs are delivered
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* before this segement.
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*/
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force_flush = 1;
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}
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/* If the driver did not pass in the checksum, set it now. */
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if (csum == 0x0000)
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@ -754,6 +767,13 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
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#endif
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}
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if (force_flush) {
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/* Timestamps mismatch; this is a FIN, etc */
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tcp_lro_active_remove(le);
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tcp_lro_flush(lc, le);
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return (TCP_LRO_CANNOT);
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}
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/* Flush now if appending will result in overflow. */
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if (le->p_len > (lc->lro_length_lim - tcp_data_len)) {
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tcp_lro_active_remove(le);
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@ -830,6 +850,14 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
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return (0);
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}
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if (force_flush) {
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/*
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* Nothing to flush, but this segment can not be further
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* aggregated/delayed.
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*/
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return (TCP_LRO_CANNOT);
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}
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/* Try to find an empty slot. */
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if (LIST_EMPTY(&lc->lro_free))
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return (TCP_LRO_NO_ENTRIES);
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