1 files changed, 854 insertions, 121 deletions

diff --git a/sys/netinet/tcp_reass.c b/sys/netinet/tcp_reass.c
index b61d2ed47f84..bc406c963fea 100644
--- a/sys/netinet/tcp_reass.c
+++ b/sys/netinet/tcp_reass.c
@@ -72,15 +72,37 @@ __FBSDID("$FreeBSD$");
 #include <netinet/tcp_seq.h>
 #include <netinet/tcp_timer.h>
 #include <netinet/tcp_var.h>
+#include <netinet/tcp_log_buf.h>
+#include <netinet/tcp_hpts.h>
 #include <netinet6/tcp6_var.h>
 #include <netinet/tcpip.h>
 #ifdef TCPDEBUG
 #include <netinet/tcp_debug.h>
 #endif /* TCPDEBUG */
 
+#define TCP_R_LOG_ADD		1
+#define TCP_R_LOG_LIMIT_REACHED 2
+#define TCP_R_LOG_APPEND	3
+#define TCP_R_LOG_PREPEND	4
+#define TCP_R_LOG_REPLACE	5
+#define TCP_R_LOG_MERGE_INTO	6
+#define TCP_R_LOG_NEW_ENTRY	7
+#define TCP_R_LOG_READ		8
+#define TCP_R_LOG_ZERO		9
+#define TCP_R_LOG_DUMP		10
+#define TCP_R_LOG_TRIM		11
+
+/* For debugging we want counters and BB logging */
+/* #define TCP_REASS_COUNTERS 1 */
+/* #define TCP_REASS_LOGGING 1 */
+
 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
     "TCP Segment Reassembly Queue");
 
+static SYSCTL_NODE(_net_inet_tcp_reass, OID_AUTO, stats, CTLFLAG_RW, 0,
+    "TCP Segment Reassembly stats");
+
+
 static int tcp_reass_maxseg = 0;
 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RDTUN,
     &tcp_reass_maxseg, 0,
@@ -96,6 +118,72 @@ SYSCTL_UINT(_net_inet_tcp_reass, OID_AUTO, maxqueuelen, CTLFLAG_RWTUN,
     &tcp_reass_maxqueuelen, 0,
     "Maximum number of TCP Segments per Reassembly Queue");
 
+static int tcp_new_limits = 0;
+SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, new_limit, CTLFLAG_RWTUN,
+    &tcp_new_limits, 0,
+    "Do we use the new limit method we are discussing?");
+
+static u_int tcp_reass_queue_guard = 16;
+SYSCTL_UINT(_net_inet_tcp_reass, OID_AUTO, queueguard, CTLFLAG_RWTUN,
+    &tcp_reass_queue_guard, 16,
+    "Number of TCP Segments in Reassembly Queue where we flip over to guard mode");
+
+#ifdef TCP_REASS_COUNTERS
+
+counter_u64_t reass_entry;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, entry, CTLFLAG_RD,
+    &reass_entry, "A segment entered reassembly ");
+
+counter_u64_t reass_path1;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path1, CTLFLAG_RD,
+    &reass_path1, "Took path 1");
+
+counter_u64_t reass_path2;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path2, CTLFLAG_RD,
+    &reass_path2, "Took path 2");
+
+counter_u64_t reass_path3;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path3, CTLFLAG_RD,
+    &reass_path3, "Took path 3");
+
+counter_u64_t reass_path4;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path4, CTLFLAG_RD,
+    &reass_path4, "Took path 4");
+
+counter_u64_t reass_path5;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path5, CTLFLAG_RD,
+    &reass_path5, "Took path 5");
+
+counter_u64_t reass_path6;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path6, CTLFLAG_RD,
+    &reass_path6, "Took path 6");
+
+counter_u64_t reass_path7;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path7, CTLFLAG_RD,
+    &reass_path7, "Took path 7");
+
+counter_u64_t reass_fullwalk;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, fullwalk, CTLFLAG_RD,
+    &reass_fullwalk, "Took a full walk ");
+
+counter_u64_t reass_nospace;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, nospace, CTLFLAG_RD,
+    &reass_nospace, "Had no mbuf capacity ");
+
+counter_u64_t merge_fwd;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, merge_fwd, CTLFLAG_RD,
+    &merge_fwd, "Ran merge fwd");
+
+counter_u64_t merge_into;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, merge_into, CTLFLAG_RD,
+    &merge_into, "Ran merge into");
+
+counter_u64_t tcp_zero_input;
+SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, zero_input, CTLFLAG_RD,
+    &tcp_zero_input, "The reassembly buffer saw a zero len segment etc");
+
+#endif
+
 /* Initialize TCP reassembly queue */
 static void
 tcp_reass_zone_change(void *tag)
@@ -107,6 +195,77 @@ tcp_reass_zone_change(void *tag)
 	    tcp_reass_maxseg);
 }
 
+#ifdef TCP_REASS_LOGGING
+
+static void
+tcp_log_reassm(struct tcpcb *tp, struct tseg_qent *q, struct tseg_qent *p,
+    tcp_seq seq, int len, uint8_t action, int instance)
+{
+	uint32_t cts;
+	struct timeval tv;
+
+	if (tp->t_logstate != TCP_LOG_STATE_OFF) {
+		union tcp_log_stackspecific log;
+
+		memset(&log, 0, sizeof(log));
+		cts = tcp_get_usecs(&tv);
+		log.u_bbr.flex1 = seq;
+		log.u_bbr.cur_del_rate = (uint64_t)q;
+		log.u_bbr.delRate = (uint64_t)p;
+		if (q != NULL) {
+			log.u_bbr.flex2 = q->tqe_start;
+			log.u_bbr.flex3 = q->tqe_len;
+			log.u_bbr.flex4 = q->tqe_mbuf_cnt;
+			log.u_bbr.hptsi_gain = q->tqe_flags;
+		}
+		if (p != NULL)  {
+			log.u_bbr.flex5 = p->tqe_start;
+			log.u_bbr.pkts_out = p->tqe_len;
+			log.u_bbr.epoch = p->tqe_mbuf_cnt;
+			log.u_bbr.cwnd_gain = p->tqe_flags;
+		}
+		log.u_bbr.flex6 = tp->t_segqmbuflen;
+		log.u_bbr.flex7 = instance;
+		log.u_bbr.flex8 = action;
+		log.u_bbr.timeStamp = cts;
+		TCP_LOG_EVENTP(tp, NULL,
+		    &tp->t_inpcb->inp_socket->so_rcv,
+		    &tp->t_inpcb->inp_socket->so_snd,
+		    TCP_LOG_REASS, 0,
+		    len, &log, false, &tv);
+	}
+}
+
+static void
+tcp_reass_log_dump(struct tcpcb *tp)
+{
+	struct tseg_qent *q;
+
+	if (tp->t_logstate != TCP_LOG_STATE_OFF) {
+		TAILQ_FOREACH(q, &tp->t_segq, tqe_q) {
+			tcp_log_reassm(tp, q, NULL, q->tqe_start, q->tqe_len, TCP_R_LOG_DUMP, 0);
+		}
+	};
+}
+
+static void
+tcp_reass_log_new_in(struct tcpcb *tp, tcp_seq seq, int len, struct mbuf *m,
+    int logval, struct tseg_qent *q)
+{
+	int cnt;
+	struct mbuf *t;
+
+	cnt = 0;
+	t = m;
+	while (t) {
+		cnt += t->m_len;
+		t = t->m_next;
+	}
+	tcp_log_reassm(tp, q, NULL, seq, len, logval, cnt);
+}
+
+#endif
+
 void
 tcp_reass_global_init(void)
 {
@@ -119,8 +278,24 @@ tcp_reass_global_init(void)
 	/* Set the zone limit and read back the effective value. */
 	tcp_reass_maxseg = uma_zone_set_max(tcp_reass_zone,
 	    tcp_reass_maxseg);
+#ifdef TCP_REASS_COUNTERS
+	reass_path1 = counter_u64_alloc(M_WAITOK);
+	reass_path2 = counter_u64_alloc(M_WAITOK);
+	reass_path3 = counter_u64_alloc(M_WAITOK);
+	reass_path4 = counter_u64_alloc(M_WAITOK);
+	reass_path5 = counter_u64_alloc(M_WAITOK);
+	reass_path6 = counter_u64_alloc(M_WAITOK);
+	reass_path7 = counter_u64_alloc(M_WAITOK);
+	reass_fullwalk = counter_u64_alloc(M_WAITOK);
+	reass_nospace = counter_u64_alloc(M_WAITOK);
+	reass_entry = counter_u64_alloc(M_WAITOK);
+	merge_fwd = counter_u64_alloc(M_WAITOK);
+	merge_into = counter_u64_alloc(M_WAITOK);
+	tcp_zero_input = counter_u64_alloc(M_WAITOK);
+#endif
 	EVENTHANDLER_REGISTER(nmbclusters_change,
 	    tcp_reass_zone_change, NULL, EVENTHANDLER_PRI_ANY);
+
 }
 
 void
@@ -130,32 +305,237 @@ tcp_reass_flush(struct tcpcb *tp)
 
 	INP_WLOCK_ASSERT(tp->t_inpcb);
 
-	while ((qe = LIST_FIRST(&tp->t_segq)) != NULL) {
-		LIST_REMOVE(qe, tqe_q);
+	while ((qe = TAILQ_FIRST(&tp->t_segq)) != NULL) {
+		TAILQ_REMOVE(&tp->t_segq, qe, tqe_q);
 		m_freem(qe->tqe_m);
 		uma_zfree(tcp_reass_zone, qe);
 		tp->t_segqlen--;
 	}
-
+	tp->t_segqmbuflen = 0;
 	KASSERT((tp->t_segqlen == 0),
 	    ("TCP reass queue %p segment count is %d instead of 0 after flush.",
 	    tp, tp->t_segqlen));
 }
 
+static void
+tcp_reass_append(struct tcpcb *tp, struct tseg_qent *last,
+    struct mbuf *m, struct tcphdr *th, int tlen, 
+    struct mbuf *mlast, int lenofoh)
+{
+
+#ifdef TCP_REASS_LOGGING
+	tcp_log_reassm(tp, last, NULL, th->th_seq, tlen, TCP_R_LOG_APPEND, 0);
+#endif
+	last->tqe_len += tlen;
+	last->tqe_m->m_pkthdr.len += tlen;
+	/* Preserve the FIN bit if its there */
+	last->tqe_flags |= (th->th_flags & TH_FIN);
+	last->tqe_last->m_next = m;
+	last->tqe_last = mlast;
+	last->tqe_mbuf_cnt += lenofoh;
+	tp->t_rcvoopack++;
+	TCPSTAT_INC(tcps_rcvoopack);
+	TCPSTAT_ADD(tcps_rcvoobyte, tlen);
+#ifdef TCP_REASS_LOGGING
+	tcp_reass_log_new_in(tp, last->tqe_start, lenofoh, last->tqe_m,
+			     TCP_R_LOG_APPEND,
+			     last);
+#endif
+}
+
+static void
+tcp_reass_prepend(struct tcpcb *tp, struct tseg_qent *first, struct mbuf *m, struct tcphdr *th,
+		  int tlen, struct mbuf *mlast, int lenofoh)
+{
+	int i;
+	
+#ifdef TCP_REASS_LOGGING
+	tcp_log_reassm(tp, first, NULL, th->th_seq, tlen, TCP_R_LOG_PREPEND, 0);
+#endif
+	if (SEQ_GT((th->th_seq + tlen), first->tqe_start)) {
+		/* The new data overlaps into the old */
+		i = (th->th_seq + tlen) - first->tqe_start;
+#ifdef TCP_REASS_LOGGING
+		tcp_log_reassm(tp, first, NULL, 0, i, TCP_R_LOG_TRIM, 1);
+#endif
+		m_adj(first->tqe_m, i);
+		first->tqe_len -= i;
+		first->tqe_start += i;
+	}
+	/* Ok now setup our chain to point to the old first */
+	mlast->m_next = first->tqe_m;
+	first->tqe_m = m;
+	first->tqe_len += tlen;
+	first->tqe_start = th->th_seq;
+	first->tqe_m->m_pkthdr.len = first->tqe_len;
+	first->tqe_mbuf_cnt += lenofoh;
+	tp->t_rcvoopack++;
+	TCPSTAT_INC(tcps_rcvoopack);
+	TCPSTAT_ADD(tcps_rcvoobyte, tlen);
+#ifdef TCP_REASS_LOGGING
+	tcp_reass_log_new_in(tp, first->tqe_start, lenofoh, first->tqe_m,
+			     TCP_R_LOG_PREPEND,
+			     first);
+#endif
+}
+
+static void 
+tcp_reass_replace(struct tcpcb *tp, struct tseg_qent *q, struct mbuf *m,
+    tcp_seq seq, int len, struct mbuf *mlast, int mbufoh, uint8_t flags)
+{
+	/*
+	 * Free the data in q, and replace
+	 * it with the new segment.
+	 */
+	int len_dif;
+
+#ifdef TCP_REASS_LOGGING
+	tcp_log_reassm(tp, q, NULL, seq, len, TCP_R_LOG_REPLACE, 0);
+#endif
+	m_freem(q->tqe_m);
+	KASSERT(tp->t_segqmbuflen >= q->tqe_mbuf_cnt,
+		("Tp:%p seg queue goes negative", tp));
+	tp->t_segqmbuflen -= q->tqe_mbuf_cnt;		       
+	q->tqe_mbuf_cnt = mbufoh;
+	q->tqe_m = m;
+	q->tqe_last = mlast;
+	q->tqe_start = seq;
+	if (len > q->tqe_len)
+		len_dif = len - q->tqe_len;
+	else
+		len_dif = 0;
+	tp->t_rcvoopack++;
+	TCPSTAT_INC(tcps_rcvoopack);
+	TCPSTAT_ADD(tcps_rcvoobyte, len_dif);
+	q->tqe_len = len;
+	q->tqe_flags = (flags & TH_FIN);
+	q->tqe_m->m_pkthdr.len = q->tqe_len;
+	tp->t_segqmbuflen += mbufoh;
+
+}
+
+static void
+tcp_reass_merge_into(struct tcpcb *tp, struct tseg_qent *ent,
+    struct tseg_qent *q)
+{
+	/* 
+	 * Merge q into ent and free q from the list.
+	 */
+#ifdef TCP_REASS_LOGGING
+	tcp_log_reassm(tp, q, ent, 0, 0, TCP_R_LOG_MERGE_INTO, 0);
+#endif
+#ifdef TCP_REASS_COUNTERS
+	counter_u64_add(merge_into, 1);
+#endif
+	ent->tqe_last->m_next = q->tqe_m;
+	ent->tqe_last = q->tqe_last;
+	ent->tqe_len += q->tqe_len;
+	ent->tqe_mbuf_cnt += q->tqe_mbuf_cnt;
+	ent->tqe_m->m_pkthdr.len += q->tqe_len;
+	ent->tqe_flags |= (q->tqe_flags & TH_FIN);
+	TAILQ_REMOVE(&tp->t_segq, q, tqe_q);
+	uma_zfree(tcp_reass_zone, q);
+	tp->t_segqlen--;
+
+}
+
+static void
+tcp_reass_merge_forward(struct tcpcb *tp, struct tseg_qent *ent)
+{
+	struct tseg_qent *q, *qtmp;
+	int i;
+	tcp_seq max;
+	/*
+	 * Given an entry merge forward anyplace
+	 * that ent overlaps forward.
+	 */
+
+	max = ent->tqe_start + ent->tqe_len;
+	q = TAILQ_NEXT(ent, tqe_q);
+	if (q == NULL) {
+		/* Nothing left */
+		return;
+	}
+	TAILQ_FOREACH_FROM_SAFE(q, &tp->t_segq, tqe_q, qtmp) {
+		if (SEQ_GT(q->tqe_start, max)) {
+			/* Beyond q */
+			break;
+		}
+		/* We have some or all that are overlapping */
+		if (SEQ_GEQ(max, (q->tqe_start + q->tqe_len))) {
+			/* It consumes it all */
+			tp->t_segqmbuflen -= q->tqe_mbuf_cnt;
+			m_freem(q->tqe_m);
+			TAILQ_REMOVE(&tp->t_segq, q, tqe_q);
+			uma_zfree(tcp_reass_zone, q);
+			tp->t_segqlen--;
+			continue;
+		}
+		/* 
+		 * Trim the q entry to dovetail to this one 
+		 * and then merge q into ent updating max
+		 * in the process.
+		 */
+		i = max - q->tqe_start;
+#ifdef TCP_REASS_LOGGING
+		tcp_log_reassm(tp, q, NULL, 0, i, TCP_R_LOG_TRIM, 2);
+#endif
+		m_adj(q->tqe_m, i);
+		q->tqe_len -= i;
+		q->tqe_start += i;
+		tcp_reass_merge_into(tp, ent, q);
+		max = ent->tqe_start + ent->tqe_len;
+	}
+#ifdef TCP_REASS_COUNTERS
+	counter_u64_add(merge_fwd, 1);
+#endif
+}
+
+static int 
+tcp_reass_overhead_of_chain(struct mbuf *m, struct mbuf **mlast)
+{
+	int len = MSIZE;
+
+	if (m->m_flags & M_EXT)
+		len += m->m_ext.ext_size;
+	while (m->m_next != NULL) {
+		m = m->m_next;
+		len += MSIZE;
+		if (m->m_flags & M_EXT)
+			len += m->m_ext.ext_size;
+	}
+	*mlast = m;
+	return (len);
+}
+
+
+/*
+ * NOTE!!! the new tcp-reassembly code *must not* use
+ * m_adj() with a negative index. That alters the chain
+ * of mbufs (by possibly chopping trailing mbufs). At
+ * the front of tcp_reass we count the mbuf overhead
+ * and setup the tail pointer. If we use m_adj(m, -5)
+ * we could corrupt the tail pointer. Currently the
+ * code only uses m_adj(m, postive-num). If this
+ * changes appropriate changes to update mlast would
+ * be needed.
+ */
 int
-tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
+tcp_reass(struct tcpcb *tp, struct tcphdr *th, tcp_seq *seq_start,
+	  int *tlenp, struct mbuf *m)
 {
-	struct tseg_qent *q;
+	struct tseg_qent *q, *last, *first;
 	struct tseg_qent *p = NULL;
-	struct tseg_qent *nq;
+	struct tseg_qent *nq = NULL;
 	struct tseg_qent *te = NULL;
+	struct tseg_qent tqs;
+	struct mbuf *mlast = NULL;
+	struct sockbuf *sb;
 	struct socket *so = tp->t_inpcb->inp_socket;
 	char *s = NULL;
-	int flags;
-	struct tseg_qent tqs;
+	int flags, i, lenofoh;
 
 	INP_WLOCK_ASSERT(tp->t_inpcb);
-
 	/*
 	 * XXX: tcp_reass() is rather inefficient with its data structures
 	 * and should be rewritten (see NetBSD for optimizations).
@@ -167,154 +547,475 @@ tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
 	 */
 	if (th == NULL)
 		goto present;
-
+	KASSERT(SEQ_GEQ(th->th_seq, tp->rcv_nxt),
+		("Attempt to add old entry to reassembly queue (th=%p, tp=%p)",
+		 th, tp));
+#ifdef TCP_REASS_LOGGING
+	tcp_reass_log_new_in(tp, th->th_seq, *tlenp, m, TCP_R_LOG_ADD, NULL);
+#endif
+#ifdef TCP_REASS_COUNTERS
+	counter_u64_add(reass_entry, 1);
+#endif
 	/*
-	 * Limit the number of segments that can be queued to reduce the
-	 * potential for mbuf exhaustion. For best performance, we want to be
-	 * able to queue a full window's worth of segments. The size of the
-	 * socket receive buffer determines our advertised window and grows
-	 * automatically when socket buffer autotuning is enabled. Use it as the
-	 * basis for our queue limit.
-	 *
-	 * However, allow the user to specify a ceiling for the number of
-	 * segments in each queue.
-	 *
-	 * Always let the missing segment through which caused this queue.
-	 * NB: Access to the socket buffer is left intentionally unlocked as we
-	 * can tolerate stale information here.
-	 *
-	 * XXXLAS: Using sbspace(so->so_rcv) instead of so->so_rcv.sb_hiwat
-	 * should work but causes packets to be dropped when they shouldn't.
-	 * Investigate why and re-evaluate the below limit after the behaviour
-	 * is understood.
+	 * Check for zero length data.
+	 */
+	if ((*tlenp == 0) && ((th->th_flags & TH_FIN) == 0)) {
+		/*
+		 * A zero length segment does no
+		 * one any good. We could check
+		 * the rcv_nxt <-> rcv_wnd but thats
+		 * already done for us by the caller.
+		 */
+#ifdef TCP_REASS_COUNTERS 
+		counter_u64_add(tcp_zero_input, 1);
+#endif
+		m_freem(m);
+#ifdef TCP_REASS_LOGGING
+		tcp_reass_log_dump(tp);
+#endif
+		return (0);
+	}
+	/*
+	 * Will it fit?
 	 */
-	if ((th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) &&
-	    tp->t_segqlen >= min((so->so_rcv.sb_hiwat / tp->t_maxseg) + 1,
-	    tcp_reass_maxqueuelen)) {
+	lenofoh = tcp_reass_overhead_of_chain(m, &mlast);
+	sb = &tp->t_inpcb->inp_socket->so_rcv;
+	if ((sb->sb_mbcnt + tp->t_segqmbuflen + lenofoh) > sb->sb_mbmax) {
+		/* No room */
 		TCPSTAT_INC(tcps_rcvreassfull);
-		*tlenp = 0;
-		if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
-			log(LOG_DEBUG, "%s; %s: queue limit reached, "
-			    "segment dropped\n", s, __func__);
-			free(s, M_TCPLOG);
-		}
+#ifdef TCP_REASS_COUNTERS
+		counter_u64_add(reass_nospace, 1);
+#endif
+#ifdef TCP_REASS_LOGGING
+		tcp_log_reassm(tp, NULL, NULL, th->th_seq, lenofoh, TCP_R_LOG_LIMIT_REACHED, 0);
+#endif
 		m_freem(m);
+		*tlenp = 0;
+#ifdef TCP_REASS_LOGGING
+		tcp_reass_log_dump(tp);
+#endif
 		return (0);
 	}
-
 	/*
-	 * Allocate a new queue entry. If we can't, or hit the zone limit
-	 * just drop the pkt.
-	 *
-	 * Use a temporary structure on the stack for the missing segment
-	 * when the zone is exhausted. Otherwise we may get stuck.
+	 * First lets deal with two common cases, the
+	 * segment appends to the back of our collected
+	 * segments. Or the segment is the next in line.
 	 */
-	te = uma_zalloc(tcp_reass_zone, M_NOWAIT);
-	if (te == NULL) {
-		if (th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) {
-			TCPSTAT_INC(tcps_rcvmemdrop);
-			m_freem(m);
+	last = TAILQ_LAST_FAST(&tp->t_segq, tseg_qent, tqe_q);
+	if (last != NULL) {
+		if ((th->th_flags & TH_FIN) &&
+		    SEQ_LT((th->th_seq + *tlenp), (last->tqe_start + last->tqe_len))) {
+			/* 
+			 * Someone is trying to game us, dump
+			 * the segment.
+			 */
 			*tlenp = 0;
-			if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
-			    NULL))) {
-				log(LOG_DEBUG, "%s; %s: global zone limit "
-				    "reached, segment dropped\n", s, __func__);
-				free(s, M_TCPLOG);
+			m_freem(m);
+			return (0);
+		}
+		if ((SEQ_GEQ(th->th_seq, last->tqe_start)) &&
+		    (SEQ_GEQ((last->tqe_start + last->tqe_len), th->th_seq))) {
+			/* Common case, trailing segment is added */
+			/**
+			 *                                 +--last
+			 *                                 v
+			 *  reassembly buffer |---|  |---| |---|
+			 *  new segment                       |---|
+			 */
+#ifdef TCP_REASS_COUNTERS
+			counter_u64_add(reass_path1, 1);
+#endif
+			if (SEQ_GT((last->tqe_start + last->tqe_len), th->th_seq)) {
+				i = (last->tqe_start + last->tqe_len) - th->th_seq;
+				if (i < *tlenp) {
+#ifdef TCP_REASS_LOGGING
+					tcp_log_reassm(tp, last, NULL, 0, i, TCP_R_LOG_TRIM, 3);
+					th->th_seq += i;
+#endif
+					m_adj(m, i);
+					*tlenp -= i;
+				} else {
+					/* Complete overlap */
+					TCPSTAT_INC(tcps_rcvduppack);
+					TCPSTAT_ADD(tcps_rcvdupbyte, *tlenp);
+					m_freem(m);
+					*tlenp = last->tqe_len;
+					*seq_start = last->tqe_start;
+					return (0);
+				}
 			}
+			if (last->tqe_flags & TH_FIN) {
+				/* 
+				 * We have data after the FIN on the last? 
+				 */
+				*tlenp = 0;
+				m_freem(m);
+				return(0);
+			}
+			tcp_reass_append(tp, last, m, th, *tlenp, mlast, lenofoh);
+			tp->t_segqmbuflen += lenofoh;
+			*seq_start = last->tqe_start;
+			*tlenp = last->tqe_len;
 			return (0);
-		} else {
-			bzero(&tqs, sizeof(struct tseg_qent));
-			te = &tqs;
-			if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
-			    NULL))) {
-				log(LOG_DEBUG,
-				    "%s; %s: global zone limit reached, using "
-				    "stack for missing segment\n", s, __func__);
-				free(s, M_TCPLOG);
+		} else if (SEQ_GT(th->th_seq, (last->tqe_start + last->tqe_len))) {
+			/* 
+			 * Second common case, we missed
+			 * another one and have something more
+			 * for the end.
+			 */
+			/**
+			 *                                 +--last
+			 *                                 v
+			 *  reassembly buffer |---|  |---| |---|
+			 *  new segment                           |---|
+			 */
+			if (last->tqe_flags & TH_FIN) {
+				/* 
+				 * We have data after the FIN on the last? 
+				 */
+				*tlenp = 0;
+				m_freem(m);
+				return(0);
 			}
+#ifdef TCP_REASS_COUNTERS
+			counter_u64_add(reass_path2, 1);
+#endif
+			p = last;
+			goto new_entry;
 		}
+	} else {
+		/* First segment (it's NULL). */
+		goto new_entry;
 	}
-	tp->t_segqlen++;
+	first = TAILQ_FIRST(&tp->t_segq);
+	if (SEQ_LT(th->th_seq, first->tqe_start) &&
+	    SEQ_GEQ((th->th_seq + *tlenp),first->tqe_start) &&
+	    SEQ_LT((th->th_seq + *tlenp), (first->tqe_start + first->tqe_len))) {
+		/*
+		 * The head of the queue is prepended by this and
+		 * it may be the one I want most.
+		 */
+		/**
+		 *       first-------+
+		 *                   v
+		 *  rea:             |---|  |---| |---|
+		 *  new:         |---|
+		 * Note the case we do not deal with here is:
+		 *   rea=     |---|   |---|   |---|
+		 *   new=  |----|
+		 * Due to the fact that it could be
+		 *   new   |--------------------|
+		 * And we might need to merge forward.
+		 */
+#ifdef INVARIANTS
+		struct mbuf *firstmbuf;
+#endif
 
+#ifdef TCP_REASS_COUNTERS
+		counter_u64_add(reass_path3, 1);
+#endif
+		if (SEQ_LT(th->th_seq, tp->rcv_nxt)) {
+			/* 
+			 * The resend was even before 
+			 * what we have. We need to trim it.
+			 * Note TSNH (it should be trimmed
+			 * before the call to tcp_reass()).
+			 */
+#ifdef INVARIANTS
+			panic("th->th_seq:%u rcv_nxt:%u tp:%p not pre-trimmed",
+			      th->th_seq, tp->rcv_nxt, tp);
+#else
+			i = tp->rcv_nxt - th->th_seq;
+#ifdef TCP_REASS_LOGGING
+			tcp_log_reassm(tp, first, NULL, 0, i, TCP_R_LOG_TRIM, 4);
+#endif
+			m_adj(m, i);
+			th->th_seq += i;
+			*tlenp -= i;
+#endif
+		}
+#ifdef INVARIANTS
+		firstmbuf = first->tqe_m;
+#endif
+		tcp_reass_prepend(tp, first, m, th, *tlenp, mlast, lenofoh);
+#ifdef INVARIANTS
+		if (firstmbuf == first->tqe_m) {
+			panic("First stayed same m:%p foobar:%p first->tqe_m:%p tp:%p first:%p",
+			      m, firstmbuf, first->tqe_m, tp, first);
+		} else if (first->tqe_m != m) {
+			panic("First did not change to m:%p foobar:%p first->tqe_m:%p tp:%p first:%p",
+			      m, firstmbuf, first->tqe_m, tp, first);
+		}
+#endif
+		tp->t_segqmbuflen += lenofoh;
+		*seq_start = first->tqe_start;
+		*tlenp = first->tqe_len;
+		goto present;
+	} else if (SEQ_LT((th->th_seq + *tlenp), first->tqe_start)) {
+		/* New segment is before our earliest segment. */
+		/**
+		 *           first---->+
+		 *                      v
+		 *  rea=                |---| ....
+		 *  new"         |---|
+		 *
+		 */
+		goto new_entry;
+	}
 	/*
 	 * Find a segment which begins after this one does.
 	 */
-	LIST_FOREACH(q, &tp->t_segq, tqe_q) {
-		if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
+#ifdef TCP_REASS_COUNTERS
+	counter_u64_add(reass_fullwalk, 1);
+#endif
+	TAILQ_FOREACH(q, &tp->t_segq, tqe_q) {
+		if (SEQ_GT(q->tqe_start, th->th_seq))
 			break;
-		p = q;
 	}
-
-	/*
-	 * If there is a preceding segment, it may provide some of
-	 * our data already.  If so, drop the data from the incoming
-	 * segment.  If it provides all of our data, drop us.
+	p = TAILQ_PREV(q, tsegqe_head, tqe_q);
+	/**
+	 * Now is this fit just in-between only? 
+	 * i.e.:
+	 *      p---+        +----q
+	 *          v        v
+	 *     res= |--|     |--|    |--|
+	 *     nee       |-|
+	 */
+	if (SEQ_LT((th->th_seq + *tlenp), q->tqe_start) &&
+	    ((p == NULL) || (SEQ_GT(th->th_seq, (p->tqe_start + p->tqe_len))))) {
+		/* Yep no overlap */
+		goto new_entry;
+	}
+	/**
+	 * If we reach here we have some (possibly all) overlap
+	 * such as:
+	 *     res=     |--|     |--|    |--|
+	 *     new=  |----|
+	 * or  new=  |-----------------|
+	 * or  new=      |--------|
+	 * or  new=            |---|
+	 * or  new=            |-----------|
 	 */
-	if (p != NULL) {
-		int i;
+	if ((p != NULL) &&
+	    (SEQ_LEQ(th->th_seq, (p->tqe_start + p->tqe_len)))) {
 		/* conversion to int (in i) handles seq wraparound */
-		i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
-		if (i > 0) {
+
+#ifdef TCP_REASS_COUNTERS
+		counter_u64_add(reass_path4, 1);
+#endif
+		i = p->tqe_start + p->tqe_len - th->th_seq;
+		if (i >= 0) {
 			if (i >= *tlenp) {
+				/**
+				 *       prev seg---->+
+				 *                    v
+				 *  reassembly buffer |---|
+				 *  new segment        |-|
+				 */
 				TCPSTAT_INC(tcps_rcvduppack);
 				TCPSTAT_ADD(tcps_rcvdupbyte, *tlenp);
+				*tlenp = p->tqe_len;
+				*seq_start = p->tqe_start;
 				m_freem(m);
-				if (te != &tqs)
-					uma_zfree(tcp_reass_zone, te);
-				tp->t_segqlen--;
 				/*
 				 * Try to present any queued data
 				 * at the left window edge to the user.
 				 * This is needed after the 3-WHS
-				 * completes.
+				 * completes. Note this probably
+				 * will not work and we will return.
 				 */
-				goto present;	/* ??? */
+				return (0);
 			}
-			m_adj(m, i);
-			*tlenp -= i;
-			th->th_seq += i;
+			if (i > 0) {
+				/**
+				 *       prev seg---->+
+				 *                    v
+				 *  reassembly buffer |---|
+				 *  new segment         |-----|
+				 */
+#ifdef TCP_REASS_COUNTERS
+				counter_u64_add(reass_path5, 1);
+#endif
+#ifdef TCP_REASS_LOGGING
+				tcp_log_reassm(tp, p, NULL, 0, i, TCP_R_LOG_TRIM, 5);
+#endif
+				m_adj(m, i);
+				*tlenp -= i;
+				th->th_seq += i;
+			}
+		}
+		if (th->th_seq == (p->tqe_start + p->tqe_len)) {
+			/* 
+			 * If dovetails in with this one 
+			 * append it.
+			 */
+			/**
+			 *       prev seg---->+
+			 *                    v
+			 *  reassembly buffer |--|     |---|
+			 *  new segment          |--|
+			 * (note: it was trimmed above if it overlapped)
+			 */
+			tcp_reass_append(tp, p, m, th, *tlenp, mlast, lenofoh);
+			tp->t_segqmbuflen += lenofoh;
+		} else {
+#ifdef INVARIANTS
+			panic("Impossible cut th_seq:%u p->seq:%u(%d) p:%p tp:%p",
+			      th->th_seq, p->tqe_start, p->tqe_len,
+			      p, tp);
+#endif
+			*tlenp = 0;
+			m_freem(m);
+			return (0);
+		}
+		q = p;
+	} else {
+		/*
+		 * The new data runs over the 
+		 * top of previously sack'd data (in q).
+		 * It may be partially overlapping, or
+		 * it may overlap the entire segment.
+		 */
+#ifdef TCP_REASS_COUNTERS
+		counter_u64_add(reass_path6, 1);
+#endif
+		if (SEQ_GEQ((th->th_seq + *tlenp), (q->tqe_start + q->tqe_len))) {
+			/* It consumes it all */
+			/**
+			 *             next seg---->+
+			 *                          v
+			 *  reassembly buffer |--|     |---|
+			 *  new segment              |----------|
+			 */
+#ifdef TCP_REASS_COUNTERS
+			counter_u64_add(reass_path7, 1);
+#endif
+			tcp_reass_replace(tp, q, m, th->th_seq, *tlenp, mlast, lenofoh, th->th_flags);
+		} else {
+			/* 
+			 * We just need to prepend the data
+			 * to this. It does not overrun
+			 * the end.
+			 */
+			/**
+			 *                next seg---->+
+			 *                             v
+			 *  reassembly buffer |--|     |---|
+			 *  new segment                   |----------|
+			 */
+			tcp_reass_prepend(tp, q, m, th, *tlenp, mlast, lenofoh);
+			tp->t_segqmbuflen += lenofoh;
 		}
 	}
-	tp->t_rcvoopack++;
-	TCPSTAT_INC(tcps_rcvoopack);
-	TCPSTAT_ADD(tcps_rcvoobyte, *tlenp);
+	/* Now does it go further than that? */
+	tcp_reass_merge_forward(tp, q);
+	*seq_start = q->tqe_start;
+	*tlenp = q->tqe_len;
+	goto present;
 
-	/*
-	 * While we overlap succeeding segments trim them or,
-	 * if they are completely covered, dequeue them.
+	/* 
+	 * When we reach here we can't combine it 
+	 * with any existing segment.
+	 *
+	 * Limit the number of segments that can be queued to reduce the
+	 * potential for mbuf exhaustion. For best performance, we want to be
+	 * able to queue a full window's worth of segments. The size of the
+	 * socket receive buffer determines our advertised window and grows
+	 * automatically when socket buffer autotuning is enabled. Use it as the
+	 * basis for our queue limit.
+	 *
+	 * However, allow the user to specify a ceiling for the number of
+	 * segments in each queue.
+	 *
+	 * Always let the missing segment through which caused this queue.
+	 * NB: Access to the socket buffer is left intentionally unlocked as we
+	 * can tolerate stale information here.
+	 *
+	 * XXXLAS: Using sbspace(so->so_rcv) instead of so->so_rcv.sb_hiwat
+	 * should work but causes packets to be dropped when they shouldn't.
+	 * Investigate why and re-evaluate the below limit after the behaviour
+	 * is understood.
 	 */
-	while (q) {
-		int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
-		if (i <= 0)
-			break;
-		if (i < q->tqe_len) {
-			q->tqe_th->th_seq += i;
-			q->tqe_len -= i;
-			m_adj(q->tqe_m, i);
-			break;
+new_entry:
+	if (tcp_new_limits) {
+		if ((tp->t_segqlen > tcp_reass_queue_guard) &&
+		    (*tlenp < MSIZE)) {
+			/* 
+			 * This is really a lie, we are not full but
+			 * are getting a segment that is above 
+			 * guard threshold. If it is and its below
+			 * a mbuf size (256) we drop it if it
+			 * can't fill in some place.
+			 */
+			TCPSTAT_INC(tcps_rcvreassfull);
+			*tlenp = 0;
+			if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
+				log(LOG_DEBUG, "%s; %s: queue limit reached, "
+				    "segment dropped\n", s, __func__);
+				free(s, M_TCPLOG);
+			}
+			m_freem(m);
+#ifdef TCP_REASS_LOGGING
+			tcp_reass_log_dump(tp);
+#endif
+			return (0);
 		}
+	} else {
 
-		nq = LIST_NEXT(q, tqe_q);
-		LIST_REMOVE(q, tqe_q);
-		m_freem(q->tqe_m);
-		uma_zfree(tcp_reass_zone, q);
-		tp->t_segqlen--;
-		q = nq;
+		if ((th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) &&
+		    tp->t_segqlen >= min((so->so_rcv.sb_hiwat / tp->t_maxseg) + 1,
+					 tcp_reass_maxqueuelen)) {
+			TCPSTAT_INC(tcps_rcvreassfull);
+			*tlenp = 0;
+			if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
+				log(LOG_DEBUG, "%s; %s: queue limit reached, "
+				    "segment dropped\n", s, __func__);
+				free(s, M_TCPLOG);
+			}
+			m_freem(m);
+#ifdef TCP_REASS_LOGGING
+			tcp_reass_log_dump(tp);
+#endif
+			return (0);
+		}
 	}
-
+	/*
+	 * Allocate a new queue entry. If we can't, or hit the zone limit
+	 * just drop the pkt.
+	 */
+	te = uma_zalloc(tcp_reass_zone, M_NOWAIT);
+	if (te == NULL) {
+		TCPSTAT_INC(tcps_rcvmemdrop);
+		m_freem(m);
+		*tlenp = 0;
+		if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
+				       NULL))) {
+			log(LOG_DEBUG, "%s; %s: global zone limit "
+			    "reached, segment dropped\n", s, __func__);
+			free(s, M_TCPLOG);
+		}
+		return (0);
+	}
+	tp->t_segqlen++;
+	tp->t_rcvoopack++;
+	TCPSTAT_INC(tcps_rcvoopack);
+	TCPSTAT_ADD(tcps_rcvoobyte, *tlenp);
 	/* Insert the new segment queue entry into place. */
 	te->tqe_m = m;
-	te->tqe_th = th;
+	te->tqe_flags = th->th_flags;
 	te->tqe_len = *tlenp;
-
+	te->tqe_start = th->th_seq;
+	te->tqe_last = mlast;
+	te->tqe_mbuf_cnt = lenofoh;
+	tp->t_segqmbuflen += te->tqe_mbuf_cnt;
 	if (p == NULL) {
-		LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
+		TAILQ_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 	} else {
-		KASSERT(te != &tqs, ("%s: temporary stack based entry not "
-		    "first element in queue", __func__));
-		LIST_INSERT_AFTER(p, te, tqe_q);
+		TAILQ_INSERT_AFTER(&tp->t_segq, p, te, tqe_q);
 	}
-
+#ifdef TCP_REASS_LOGGING
+	tcp_reass_log_new_in(tp, th->th_seq, *tlenp, m, TCP_R_LOG_NEW_ENTRY, te);
+#endif
 present:
 	/*
 	 * Present data to user, advancing rcv_nxt through
@@ -322,24 +1023,56 @@ present:
 	 */
 	if (!TCPS_HAVEESTABLISHED(tp->t_state))
 		return (0);
-	q = LIST_FIRST(&tp->t_segq);
-	if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
+	q = TAILQ_FIRST(&tp->t_segq);
+	KASSERT(q == NULL || SEQ_GEQ(q->tqe_start, tp->rcv_nxt),
+		("Reassembly queue for %p has stale entry at head", tp));
+	if (!q || q->tqe_start != tp->rcv_nxt) {
+#ifdef TCP_REASS_LOGGING
+		tcp_reass_log_dump(tp);
+#endif
 		return (0);
+	}
 	SOCKBUF_LOCK(&so->so_rcv);
 	do {
 		tp->rcv_nxt += q->tqe_len;
-		flags = q->tqe_th->th_flags & TH_FIN;
-		nq = LIST_NEXT(q, tqe_q);
-		LIST_REMOVE(q, tqe_q);
-		if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
+		flags = q->tqe_flags & TH_FIN;
+		nq = TAILQ_NEXT(q, tqe_q);
+		TAILQ_REMOVE(&tp->t_segq, q, tqe_q);
+		if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 			m_freem(q->tqe_m);
-		else
+		} else {
+#ifdef TCP_REASS_LOGGING
+			tcp_reass_log_new_in(tp, q->tqe_start, q->tqe_len, q->tqe_m, TCP_R_LOG_READ, q);
+			tcp_log_reassm(tp, q, NULL, th->th_seq, *tlenp, TCP_R_LOG_READ, 1);
+#endif
 			sbappendstream_locked(&so->so_rcv, q->tqe_m, 0);
-		if (q != &tqs)
+		}
+#ifdef TCP_REASS_LOGGING
+		tcp_log_reassm(tp, q, NULL, th->th_seq, *tlenp, TCP_R_LOG_READ, 2);
+#endif
+		KASSERT(tp->t_segqmbuflen >= q->tqe_mbuf_cnt,
+			("tp:%p seg queue goes negative", tp));
+		tp->t_segqmbuflen -= q->tqe_mbuf_cnt;
+		if (q != &tqs) 
 			uma_zfree(tcp_reass_zone, q);
 		tp->t_segqlen--;
 		q = nq;
-	} while (q && q->tqe_th->th_seq == tp->rcv_nxt);
+	} while (q && q->tqe_start == tp->rcv_nxt);
+	if (TAILQ_EMPTY(&tp->t_segq) &&
+	    (tp->t_segqmbuflen != 0)) {
+#ifdef INVARIANTS
+		panic("tp:%p segq:%p len:%d queue empty",
+		      tp, &tp->t_segq, tp->t_segqmbuflen);
+#else
+#ifdef TCP_REASS_LOGGING
+		tcp_log_reassm(tp, NULL, NULL, th->th_seq, *tlenp, TCP_R_LOG_ZERO, 0);
+#endif
+		tp->t_segqmbuflen = 0;
+#endif
+	}
+#ifdef TCP_REASS_LOGGING
+	tcp_reass_log_dump(tp);
+#endif
 	sorwakeup_locked(so);
 	return (flags);
 }