Decompose TCP INP_INFO lock to increase short-lived TCP connections scalability:

- The existing TCP INP_INFO lock continues to protect the global inpcb list
  stability during full list traversal (e.g. tcp_pcblist()).

- A new INP_LIST lock protects inpcb list actual modifications (inp allocation
  and free) and inpcb global counters.

It allows to use TCP INP_INFO_RLOCK lock in critical paths (e.g. tcp_input())
and INP_INFO_WLOCK only in occasional operations that walk all connections.

PR:			183659
Differential Revision:	https://reviews.freebsd.org/D2599
Reviewed by:		jhb, adrian
Tested by:		adrian, nitroboost-gmail.com
Sponsored by:		Verisign, Inc.

15 files changed, 328 insertions, 241 deletions

diff --git a/sys/dev/cxgb/ulp/tom/cxgb_cpl_io.c b/sys/dev/cxgb/ulp/tom/cxgb_cpl_io.c
index bdd746fcb44f..985306c3c6e8 100644
--- a/sys/dev/cxgb/ulp/tom/cxgb_cpl_io.c
+++ b/sys/dev/cxgb/ulp/tom/cxgb_cpl_io.c
@@ -639,7 +639,7 @@ t3_send_fin(struct toedev *tod, struct tcpcb *tp)
 	unsigned int tid = toep->tp_tid;
 #endif
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(inp);
 
 	CTR4(KTR_CXGB, "%s: tid %d, toep %p, flags %x", __func__, tid, toep,
@@ -925,12 +925,12 @@ do_act_open_rpl(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 
 	rc = act_open_rpl_status_to_errno(s);
 	if (rc != EAGAIN)
-		INP_INFO_WLOCK(&V_tcbinfo);
+		INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	toe_connect_failed(tod, inp, rc);
 	toepcb_release(toep);	/* unlocks inp */
 	if (rc != EAGAIN)
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 
 	m_freem(m);
 	return (0);
@@ -1061,7 +1061,7 @@ send_reset(struct toepcb *toep)
 	struct adapter *sc = tod->tod_softc;
 	struct mbuf *m;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(inp);
 
 	CTR4(KTR_CXGB, "%s: tid %d, toep %p (%x)", __func__, tid, toep,
@@ -1172,12 +1172,12 @@ do_rx_data(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 		SOCKBUF_UNLOCK(so_rcv);
 		INP_WUNLOCK(inp);
 
-		INP_INFO_WLOCK(&V_tcbinfo);
+		INP_INFO_RLOCK(&V_tcbinfo);
 		INP_WLOCK(inp);
 		tp = tcp_drop(tp, ECONNRESET);
 		if (tp)
 			INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 
 		m_freem(m);
 		return (0);
@@ -1222,7 +1222,7 @@ do_peer_close(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 	struct tcpcb *tp;
 	struct socket *so;
 
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	tp = intotcpcb(inp);
 
@@ -1250,7 +1250,7 @@ do_peer_close(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 	case TCPS_FIN_WAIT_2:
 		tcp_twstart(tp);
 		INP_UNLOCK_ASSERT(inp);	/* safe, we have a ref on the  inp */
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 
 		INP_WLOCK(inp);
 		toepcb_release(toep);	/* no more CPLs expected */
@@ -1264,7 +1264,7 @@ do_peer_close(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 
 done:
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 
 	m_freem(m);
 	return (0);
@@ -1285,7 +1285,7 @@ do_close_con_rpl(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 	struct tcpcb *tp;
 	struct socket *so;
 
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	tp = intotcpcb(inp);
 
@@ -1303,7 +1303,7 @@ do_close_con_rpl(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 		tcp_twstart(tp);
 release:
 		INP_UNLOCK_ASSERT(inp);	/* safe, we have a ref on the  inp */
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 
 		INP_WLOCK(inp);
 		toepcb_release(toep);	/* no more CPLs expected */
@@ -1328,7 +1328,7 @@ release:
 
 done:
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 
 	m_freem(m);
 	return (0);
@@ -1489,7 +1489,7 @@ do_abort_req(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 		return (do_abort_req_synqe(qs, r, m));
 
 	inp = toep->tp_inp;
-	INP_INFO_WLOCK(&V_tcbinfo);	/* for tcp_close */
+	INP_INFO_RLOCK(&V_tcbinfo);	/* for tcp_close */
 	INP_WLOCK(inp);
 
 	tp = intotcpcb(inp);
@@ -1503,7 +1503,7 @@ do_abort_req(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 		toep->tp_flags |= TP_ABORT_REQ_RCVD;
 		toep->tp_flags |= TP_ABORT_SHUTDOWN;
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		m_freem(m);
 		return (0);
 	}
@@ -1523,7 +1523,7 @@ do_abort_req(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 			INP_WLOCK(inp);	/* re-acquire */
 		toepcb_release(toep);	/* no more CPLs expected */
 	}
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 
 	send_abort_rpl(tod, tid, qset);
 	m_freem(m);
diff --git a/sys/dev/cxgb/ulp/tom/cxgb_listen.c b/sys/dev/cxgb/ulp/tom/cxgb_listen.c
index e11bb2583373..933a83c2aaa7 100644
--- a/sys/dev/cxgb/ulp/tom/cxgb_listen.c
+++ b/sys/dev/cxgb/ulp/tom/cxgb_listen.c
@@ -541,11 +541,11 @@ do_pass_accept_req(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 			REJECT_PASS_ACCEPT();	/* no l2te, or ifp mismatch */
 	}
 
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 
 	/* Don't offload if the 4-tuple is already in use */
 	if (toe_4tuple_check(&inc, &th, ifp) != 0) {
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		REJECT_PASS_ACCEPT();
 	}
 
@@ -558,7 +558,7 @@ do_pass_accept_req(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 		 * resources tied to this listen context.
 		 */
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		REJECT_PASS_ACCEPT();
 	}
 	so = inp->inp_socket;
@@ -686,7 +686,7 @@ do_pass_establish(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 	struct toepcb *toep;
 	struct socket *so;
 	struct listen_ctx *lctx = synqe->lctx;
-	struct inpcb *inp = lctx->inp;
+	struct inpcb *inp = lctx->inp, *new_inp;
 	struct tcpopt to;
 	struct tcphdr th;
 	struct in_conninfo inc;
@@ -700,7 +700,7 @@ do_pass_establish(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 	KASSERT(qs->idx == synqe->qset,
 	    ("%s qset mismatch %d %d", __func__, qs->idx, synqe->qset));
 
-	INP_INFO_WLOCK(&V_tcbinfo);	/* for syncache_expand */
+	INP_INFO_RLOCK(&V_tcbinfo);	/* for syncache_expand */
 	INP_WLOCK(inp);
 
 	if (__predict_false(inp->inp_flags & INP_DROPPED)) {
@@ -714,7 +714,7 @@ do_pass_establish(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 		    ("%s: listen socket dropped but tid %u not aborted.",
 		    __func__, tid));
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		m_freem(m);
 		return (0);
 	}
@@ -730,7 +730,7 @@ do_pass_establish(struct sge_qset *qs, struct rsp_desc *r, struct mbuf *m)
 reset:
 		t3_send_reset_synqe(tod, synqe);
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		m_freem(m);
 		return (0);
 	}
@@ -748,21 +748,23 @@ reset:
 		goto reset;
 	}
 
-	if (__predict_false(!(synqe->flags & TP_SYNQE_EXPANDED))) {
-		struct inpcb *new_inp = sotoinpcb(so);
+	/* New connection inpcb is already locked by syncache_expand(). */
+	new_inp = sotoinpcb(so);
+	INP_WLOCK_ASSERT(new_inp);
 
-		INP_WLOCK(new_inp);
+	if (__predict_false(!(synqe->flags & TP_SYNQE_EXPANDED))) {
 		tcp_timer_activate(intotcpcb(new_inp), TT_KEEP, 0);
 		t3_offload_socket(tod, synqe, so);
-		INP_WUNLOCK(new_inp);
 	}
 
+	INP_WUNLOCK(new_inp);
+
 	/* Remove the synq entry and release its reference on the lctx */
 	TAILQ_REMOVE(&lctx->synq, synqe, link);
 	inp = release_lctx(td, lctx);
 	if (inp)
 		INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	release_synqe(synqe);
 
 	m_freem(m);
@@ -1128,7 +1130,7 @@ t3_offload_socket(struct toedev *tod, void *arg, struct socket *so)
 	struct cpl_pass_establish *cpl = synqe->cpl;
 	struct toepcb *toep = synqe->toep;
 
-	INP_INFO_LOCK_ASSERT(&V_tcbinfo); /* prevents bad race with accept() */
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo); /* prevents bad race with accept() */
 	INP_WLOCK_ASSERT(inp);
 
 	offload_socket(so, toep);
diff --git a/sys/dev/cxgbe/tom/t4_connect.c b/sys/dev/cxgbe/tom/t4_connect.c
index 425c56358e7e..fae7979db9a8 100644
--- a/sys/dev/cxgbe/tom/t4_connect.c
+++ b/sys/dev/cxgbe/tom/t4_connect.c
@@ -189,12 +189,12 @@ act_open_failure_cleanup(struct adapter *sc, u_int atid, u_int status)
 	toep->tid = -1;
 
 	if (status != EAGAIN)
-		INP_INFO_WLOCK(&V_tcbinfo);
+		INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	toe_connect_failed(tod, inp, status);
 	final_cpl_received(toep);	/* unlocks inp */
 	if (status != EAGAIN)
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 }
 
 static int
diff --git a/sys/dev/cxgbe/tom/t4_cpl_io.c b/sys/dev/cxgbe/tom/t4_cpl_io.c
index 147802d927bf..eb972d074612 100644
--- a/sys/dev/cxgbe/tom/t4_cpl_io.c
+++ b/sys/dev/cxgbe/tom/t4_cpl_io.c
@@ -1085,7 +1085,7 @@ do_peer_close(struct sge_iq *iq, const struct rss_header *rss, struct mbuf *m)
 
 	KASSERT(toep->tid == tid, ("%s: toep tid mismatch", __func__));
 
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	tp = intotcpcb(inp);
 
@@ -1127,7 +1127,7 @@ do_peer_close(struct sge_iq *iq, const struct rss_header *rss, struct mbuf *m)
 	case TCPS_FIN_WAIT_2:
 		tcp_twstart(tp);
 		INP_UNLOCK_ASSERT(inp);	 /* safe, we have a ref on the inp */
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 
 		INP_WLOCK(inp);
 		final_cpl_received(toep);
@@ -1139,7 +1139,7 @@ do_peer_close(struct sge_iq *iq, const struct rss_header *rss, struct mbuf *m)
 	}
 done:
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	return (0);
 }
 
@@ -1166,7 +1166,7 @@ do_close_con_rpl(struct sge_iq *iq, const struct rss_header *rss,
 	KASSERT(m == NULL, ("%s: wasn't expecting payload", __func__));
 	KASSERT(toep->tid == tid, ("%s: toep tid mismatch", __func__));
 
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	tp = intotcpcb(inp);
 
@@ -1184,7 +1184,7 @@ do_close_con_rpl(struct sge_iq *iq, const struct rss_header *rss,
 		tcp_twstart(tp);
 release:
 		INP_UNLOCK_ASSERT(inp);	/* safe, we have a ref on the  inp */
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 
 		INP_WLOCK(inp);
 		final_cpl_received(toep);	/* no more CPLs expected */
@@ -1208,7 +1208,7 @@ release:
 	}
 done:
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	return (0);
 }
 
@@ -1367,7 +1367,7 @@ do_abort_req(struct sge_iq *iq, const struct rss_header *rss, struct mbuf *m)
 	}
 
 	inp = toep->inp;
-	INP_INFO_WLOCK(&V_tcbinfo);	/* for tcp_close */
+	INP_INFO_RLOCK(&V_tcbinfo);	/* for tcp_close */
 	INP_WLOCK(inp);
 
 	tp = intotcpcb(inp);
@@ -1401,7 +1401,7 @@ do_abort_req(struct sge_iq *iq, const struct rss_header *rss, struct mbuf *m)
 
 	final_cpl_received(toep);
 done:
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	send_abort_rpl(sc, ofld_txq, tid, CPL_ABORT_NO_RST);
 	return (0);
 }
@@ -1515,12 +1515,12 @@ do_rx_data(struct sge_iq *iq, const struct rss_header *rss, struct mbuf *m)
 		SOCKBUF_UNLOCK(sb);
 		INP_WUNLOCK(inp);
 
-		INP_INFO_WLOCK(&V_tcbinfo);
+		INP_INFO_RLOCK(&V_tcbinfo);
 		INP_WLOCK(inp);
 		tp = tcp_drop(tp, ECONNRESET);
 		if (tp)
 			INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 
 		return (0);
 	}
diff --git a/sys/dev/cxgbe/tom/t4_listen.c b/sys/dev/cxgbe/tom/t4_listen.c
index fc5f9350db79..127abe0c1217 100644
--- a/sys/dev/cxgbe/tom/t4_listen.c
+++ b/sys/dev/cxgbe/tom/t4_listen.c
@@ -930,7 +930,7 @@ t4_offload_socket(struct toedev *tod, void *arg, struct socket *so)
 	struct cpl_pass_establish *cpl = mtod(synqe->syn, void *);
 	struct toepcb *toep = *(struct toepcb **)(cpl + 1);
 
-	INP_INFO_LOCK_ASSERT(&V_tcbinfo); /* prevents bad race with accept() */
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo); /* prevents bad race with accept() */
 	INP_WLOCK_ASSERT(inp);
 	KASSERT(synqe->flags & TPF_SYNQE,
 	    ("%s: %p not a synq_entry?", __func__, arg));
@@ -1259,15 +1259,15 @@ do_pass_accept_req(struct sge_iq *iq, const struct rss_header *rss,
 		REJECT_PASS_ACCEPT();
 	rpl = wrtod(wr);
 
-	INP_INFO_WLOCK(&V_tcbinfo);	/* for 4-tuple check */
+	INP_INFO_RLOCK(&V_tcbinfo);	/* for 4-tuple check */
 
 	/* Don't offload if the 4-tuple is already in use */
 	if (toe_4tuple_check(&inc, &th, ifp) != 0) {
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		free(wr, M_CXGBE);
 		REJECT_PASS_ACCEPT();
 	}
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 
 	inp = lctx->inp;		/* listening socket, not owned by TOE */
 	INP_WLOCK(inp);
@@ -1441,7 +1441,7 @@ do_pass_establish(struct sge_iq *iq, const struct rss_header *rss,
 	unsigned int tid = GET_TID(cpl);
 	struct synq_entry *synqe = lookup_tid(sc, tid);
 	struct listen_ctx *lctx = synqe->lctx;
-	struct inpcb *inp = lctx->inp;
+	struct inpcb *inp = lctx->inp, *new_inp;
 	struct socket *so;
 	struct tcphdr th;
 	struct tcpopt to;
@@ -1459,7 +1459,7 @@ do_pass_establish(struct sge_iq *iq, const struct rss_header *rss,
 	KASSERT(synqe->flags & TPF_SYNQE,
 	    ("%s: tid %u (ctx %p) not a synqe", __func__, tid, synqe));
 
-	INP_INFO_WLOCK(&V_tcbinfo);	/* for syncache_expand */
+	INP_INFO_RLOCK(&V_tcbinfo);	/* for syncache_expand */
 	INP_WLOCK(inp);
 
 	CTR6(KTR_CXGBE,
@@ -1475,7 +1475,7 @@ do_pass_establish(struct sge_iq *iq, const struct rss_header *rss,
 		}
 
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		return (0);
 	}
 
@@ -1500,7 +1500,7 @@ reset:
 		 */
 		send_reset_synqe(TOEDEV(ifp), synqe);
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		return (0);
 	}
 	toep->tid = tid;
@@ -1534,6 +1534,10 @@ reset:
 		goto reset;
 	}
 
+	/* New connection inpcb is already locked by syncache_expand(). */
+	new_inp = sotoinpcb(so);
+	INP_WLOCK_ASSERT(new_inp);
+
 	/*
 	 * This is for the unlikely case where the syncache entry that we added
 	 * has been evicted from the syncache, but the syncache_expand above
@@ -1544,20 +1548,18 @@ reset:
 	 * this somewhat defeats the purpose of having a tod_offload_socket :-(
 	 */
 	if (__predict_false(!(synqe->flags & TPF_SYNQE_EXPANDED))) {
-		struct inpcb *new_inp = sotoinpcb(so);
-
-		INP_WLOCK(new_inp);
 		tcp_timer_activate(intotcpcb(new_inp), TT_KEEP, 0);
 		t4_offload_socket(TOEDEV(ifp), synqe, so);
-		INP_WUNLOCK(new_inp);
 	}
 
+	INP_WUNLOCK(new_inp);
+
 	/* Done with the synqe */
 	TAILQ_REMOVE(&lctx->synq, synqe, link);
 	inp = release_lctx(sc, lctx);
 	if (inp != NULL)
 		INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	release_synqe(synqe);
 
 	return (0);
diff --git a/sys/netinet/in_pcb.c b/sys/netinet/in_pcb.c
index 965932486db3..c721c6dd950c 100644
--- a/sys/netinet/in_pcb.c
+++ b/sys/netinet/in_pcb.c
@@ -224,6 +224,7 @@ in_pcbinfo_init(struct inpcbinfo *pcbinfo, const char *name,
 
 	INP_INFO_LOCK_INIT(pcbinfo, name);
 	INP_HASH_LOCK_INIT(pcbinfo, "pcbinfohash");	/* XXXRW: argument? */
+	INP_LIST_LOCK_INIT(pcbinfo, "pcbinfolist");
 #ifdef VIMAGE
 	pcbinfo->ipi_vnet = curvnet;
 #endif
@@ -262,6 +263,7 @@ in_pcbinfo_destroy(struct inpcbinfo *pcbinfo)
 	in_pcbgroup_destroy(pcbinfo);
 #endif
 	uma_zdestroy(pcbinfo->ipi_zone);
+	INP_LIST_LOCK_DESTROY(pcbinfo);
 	INP_HASH_LOCK_DESTROY(pcbinfo);
 	INP_INFO_LOCK_DESTROY(pcbinfo);
 }
@@ -276,7 +278,14 @@ in_pcballoc(struct socket *so, struct inpcbinfo *pcbinfo)
 	struct inpcb *inp;
 	int error;
 
-	INP_INFO_WLOCK_ASSERT(pcbinfo);
+#ifdef INVARIANTS
+	if (pcbinfo == &V_tcbinfo) {
+		INP_INFO_RLOCK_ASSERT(pcbinfo);
+	} else {
+		INP_INFO_WLOCK_ASSERT(pcbinfo);
+	}
+#endif
+
 	error = 0;
 	inp = uma_zalloc(pcbinfo->ipi_zone, M_NOWAIT);
 	if (inp == NULL)
@@ -308,6 +317,8 @@ in_pcballoc(struct socket *so, struct inpcbinfo *pcbinfo)
 			inp->inp_flags |= IN6P_IPV6_V6ONLY;
 	}
 #endif
+	INP_WLOCK(inp);
+	INP_LIST_WLOCK(pcbinfo);
 	LIST_INSERT_HEAD(pcbinfo->ipi_listhead, inp, inp_list);
 	pcbinfo->ipi_count++;
 	so->so_pcb = (caddr_t)inp;
@@ -315,9 +326,9 @@ in_pcballoc(struct socket *so, struct inpcbinfo *pcbinfo)
 	if (V_ip6_auto_flowlabel)
 		inp->inp_flags |= IN6P_AUTOFLOWLABEL;
 #endif
-	INP_WLOCK(inp);
 	inp->inp_gencnt = ++pcbinfo->ipi_gencnt;
 	refcount_init(&inp->inp_refcount, 1);	/* Reference from inpcbinfo */
+	INP_LIST_WUNLOCK(pcbinfo);
 #if defined(IPSEC) || defined(MAC)
 out:
 	if (error != 0) {
@@ -1246,7 +1257,13 @@ in_pcbfree(struct inpcb *inp)
 
 	KASSERT(inp->inp_socket == NULL, ("%s: inp_socket != NULL", __func__));
 
-	INP_INFO_WLOCK_ASSERT(pcbinfo);
+#ifdef INVARIANTS
+	if (pcbinfo == &V_tcbinfo) {
+		INP_INFO_RLOCK_ASSERT(pcbinfo);
+	} else {
+		INP_INFO_WLOCK_ASSERT(pcbinfo);
+	}
+#endif
 	INP_WLOCK_ASSERT(inp);
 
 	/* XXXRW: Do as much as possible here. */
@@ -1254,8 +1271,10 @@ in_pcbfree(struct inpcb *inp)
 	if (inp->inp_sp != NULL)
 		ipsec_delete_pcbpolicy(inp);
 #endif
+	INP_LIST_WLOCK(pcbinfo);
 	inp->inp_gencnt = ++pcbinfo->ipi_gencnt;
 	in_pcbremlists(inp);
+	INP_LIST_WUNLOCK(pcbinfo);
 #ifdef INET6
 	if (inp->inp_vflag & INP_IPV6PROTO) {
 		ip6_freepcbopts(inp->in6p_outputopts);
@@ -1412,7 +1431,7 @@ in_pcbpurgeif0(struct inpcbinfo *pcbinfo, struct ifnet *ifp)
 	struct ip_moptions *imo;
 	int i, gap;
 
-	INP_INFO_RLOCK(pcbinfo);
+	INP_INFO_WLOCK(pcbinfo);
 	LIST_FOREACH(inp, pcbinfo->ipi_listhead, inp_list) {
 		INP_WLOCK(inp);
 		imo = inp->inp_moptions;
@@ -1442,7 +1461,7 @@ in_pcbpurgeif0(struct inpcbinfo *pcbinfo, struct ifnet *ifp)
 		}
 		INP_WUNLOCK(inp);
 	}
-	INP_INFO_RUNLOCK(pcbinfo);
+	INP_INFO_WUNLOCK(pcbinfo);
 }
 
 /*
@@ -2163,8 +2182,16 @@ in_pcbremlists(struct inpcb *inp)
 {
 	struct inpcbinfo *pcbinfo = inp->inp_pcbinfo;
 
-	INP_INFO_WLOCK_ASSERT(pcbinfo);
+#ifdef INVARIANTS
+	if (pcbinfo == &V_tcbinfo) {
+		INP_INFO_RLOCK_ASSERT(pcbinfo);
+	} else {
+		INP_INFO_WLOCK_ASSERT(pcbinfo);
+	}
+#endif
+
 	INP_WLOCK_ASSERT(inp);
+	INP_LIST_WLOCK_ASSERT(pcbinfo);
 
 	inp->inp_gencnt = ++pcbinfo->ipi_gencnt;
 	if (inp->inp_flags & INP_INHASHLIST) {
@@ -2309,13 +2336,13 @@ inp_apply_all(void (*func)(struct inpcb *, void *), void *arg)
 {
 	struct inpcb *inp;
 
-	INP_INFO_RLOCK(&V_tcbinfo);
+	INP_INFO_WLOCK(&V_tcbinfo);
 	LIST_FOREACH(inp, V_tcbinfo.ipi_listhead, inp_list) {
 		INP_WLOCK(inp);
 		func(inp, arg);
 		INP_WUNLOCK(inp);
 	}
-	INP_INFO_RUNLOCK(&V_tcbinfo);
+	INP_INFO_WUNLOCK(&V_tcbinfo);
 }
 
 struct socket *
diff --git a/sys/netinet/in_pcb.h b/sys/netinet/in_pcb.h
index 606795a69bb0..2b7932538615 100644
--- a/sys/netinet/in_pcb.h
+++ b/sys/netinet/in_pcb.h
@@ -130,23 +130,35 @@ struct in_conninfo {
 struct	icmp6_filter;
 
 /*-
- * struct inpcb captures the network layer state for TCP, UDP, and raw IPv4
- * and IPv6 sockets.  In the case of TCP, further per-connection state is
+ * struct inpcb captures the network layer state for TCP, UDP, and raw IPv4 and
+ * IPv6 sockets.  In the case of TCP and UDP, further per-connection state is
  * hung off of inp_ppcb most of the time.  Almost all fields of struct inpcb
  * are static after creation or protected by a per-inpcb rwlock, inp_lock.  A
- * few fields also require the global pcbinfo lock for the inpcb to be held,
- * when modified, such as the global connection lists and hashes, as well as
- * binding information (which affects which hash a connection is on).  This
- * model means that connections can be looked up without holding the
- * per-connection lock, which is important for performance when attempting to
- * find the connection for a packet given its IP and port tuple.  Writing to
- * these fields that write locks be held on both the inpcb and global locks.
+ * few fields are protected by multiple locks as indicated in the locking notes
+ * below.  For these fields, all of the listed locks must be write-locked for
+ * any modifications.  However, these fields can be safely read while any one of
+ * the listed locks are read-locked.  This model can permit greater concurrency
+ * for read operations.  For example, connections can be looked up while only
+ * holding a read lock on the global pcblist lock.  This is important for
+ * performance when attempting to find the connection for a packet given its IP
+ * and port tuple.
+ *
+ * One noteworthy exception is that the global pcbinfo lock follows a different
+ * set of rules in relation to the inp_list field.  Rather than being
+ * write-locked for modifications and read-locked for list iterations, it must
+ * be read-locked during modifications and write-locked during list iterations.
+ * This ensures that the relatively rare global list iterations safely walk a
+ * stable snapshot of connections while allowing more common list modifications
+ * to safely grab the pcblist lock just while adding or removing a connection
+ * from the global list.
  *
  * Key:
  * (c) - Constant after initialization
  * (g) - Protected by the pcbgroup lock
  * (i) - Protected by the inpcb lock
  * (p) - Protected by the pcbinfo lock for the inpcb
+ * (l) - Protected by the pcblist lock for the inpcb
+ * (h) - Protected by the pcbhash lock for the inpcb
  * (s) - Protected by another subsystem's locks
  * (x) - Undefined locking
  *
@@ -161,15 +173,21 @@ struct	icmp6_filter;
  * socket has been freed), or there may be close(2)-related races.
  *
  * The inp_vflag field is overloaded, and would otherwise ideally be (c).
+ *
+ * TODO:  Currently only the TCP stack is leveraging the global pcbinfo lock
+ * read-lock usage during modification, this model can be applied to other
+ * protocols (especially SCTP).
  */
 struct inpcb {
-	LIST_ENTRY(inpcb) inp_hash;	/* (i/p) hash list */
+	LIST_ENTRY(inpcb) inp_hash;	/* (h/i) hash list */
 	LIST_ENTRY(inpcb) inp_pcbgrouphash;	/* (g/i) hash list */
-	LIST_ENTRY(inpcb) inp_list;	/* (i/p) list for all PCBs for proto */
+	LIST_ENTRY(inpcb) inp_list;	/* (p/l) list for all PCBs for proto */
+	                                /* (p[w]) for list iteration */
+	                                /* (p[r]/l) for addition/removal */
 	void	*inp_ppcb;		/* (i) pointer to per-protocol pcb */
 	struct	inpcbinfo *inp_pcbinfo;	/* (c) PCB list info */
 	struct	inpcbgroup *inp_pcbgroup; /* (g/i) PCB group list */
-	LIST_ENTRY(inpcb) inp_pcbgroup_wild; /* (g/i/p) group wildcard entry */
+	LIST_ENTRY(inpcb) inp_pcbgroup_wild; /* (g/i/h) group wildcard entry */
 	struct	socket *inp_socket;	/* (i) back pointer to socket */
 	struct	ucred	*inp_cred;	/* (c) cache of socket cred */
 	u_int32_t inp_flow;		/* (i) IPv6 flow information */
@@ -188,7 +206,7 @@ struct inpcb {
 					 *     general use */
 
 	/* Local and foreign ports, local and foreign addr. */
-	struct	in_conninfo inp_inc;	/* (i/p) list for PCB's local port */
+	struct	in_conninfo inp_inc;	/* (i) list for PCB's local port */
 
 	/* MAC and IPSEC policy information. */
 	struct	label *inp_label;	/* (i) MAC label */
@@ -213,8 +231,8 @@ struct inpcb {
 		int	inp6_cksum;
 		short	inp6_hops;
 	} inp_depend6;
-	LIST_ENTRY(inpcb) inp_portlist;	/* (i/p) */
-	struct	inpcbport *inp_phd;	/* (i/p) head of this list */
+	LIST_ENTRY(inpcb) inp_portlist;	/* (i/h) */
+	struct	inpcbport *inp_phd;	/* (i/h) head of this list */
 #define inp_zero_size offsetof(struct inpcb, inp_gencnt)
 	inp_gen_t	inp_gencnt;	/* (c) generation count */
 	struct llentry	*inp_lle;	/* cached L2 information */
@@ -279,37 +297,46 @@ struct inpcbport {
  * Global data structure for each high-level protocol (UDP, TCP, ...) in both
  * IPv4 and IPv6.  Holds inpcb lists and information for managing them.
  *
- * Each pcbinfo is protected by two locks: ipi_lock and ipi_hash_lock,
- * the former covering mutable global fields (such as the global pcb list),
- * and the latter covering the hashed lookup tables.  The lock order is:
+ * Each pcbinfo is protected by three locks: ipi_lock, ipi_hash_lock and
+ * ipi_list_lock:
+ *  - ipi_lock covering the global pcb list stability during loop iteration,
+ *  - ipi_hash_lock covering the hashed lookup tables,
+ *  - ipi_list_lock covering mutable global fields (such as the global
+ *    pcb list)
+ *
+ * The lock order is:
  *
- *    ipi_lock (before) inpcb locks (before) {ipi_hash_lock, pcbgroup locks}
+ *    ipi_lock (before)
+ *        inpcb locks (before)
+ *            ipi_list locks (before)
+ *                {ipi_hash_lock, pcbgroup locks}
  *
  * Locking key:
  *
  * (c) Constant or nearly constant after initialisation
  * (g) Locked by ipi_lock
+ * (l) Locked by ipi_list_lock
  * (h) Read using either ipi_hash_lock or inpcb lock; write requires both
  * (p) Protected by one or more pcbgroup locks
  * (x) Synchronisation properties poorly defined
  */
 struct inpcbinfo {
 	/*
-	 * Global lock protecting global inpcb list, inpcb count, etc.
+	 * Global lock protecting full inpcb list traversal
 	 */
 	struct rwlock		 ipi_lock;
 
 	/*
 	 * Global list of inpcbs on the protocol.
 	 */
-	struct inpcbhead	*ipi_listhead;		/* (g) */
-	u_int			 ipi_count;		/* (g) */
+	struct inpcbhead	*ipi_listhead;		/* (g/l) */
+	u_int			 ipi_count;		/* (l) */
 
 	/*
 	 * Generation count -- incremented each time a connection is allocated
 	 * or freed.
 	 */
-	u_quad_t		 ipi_gencnt;		/* (g) */
+	u_quad_t		 ipi_gencnt;		/* (l) */
 
 	/*
 	 * Fields associated with port lookup and allocation.
@@ -367,6 +394,11 @@ struct inpcbinfo {
 	 * general use 2
 	 */
 	void 			*ipi_pspare[2];
+
+	/*
+	 * Global lock protecting global inpcb list, inpcb count, etc.
+	 */
+	struct rwlock		 ipi_list_lock;
 };
 
 #ifdef _KERNEL
@@ -466,6 +498,25 @@ short	inp_so_options(const struct inpcb *inp);
 #define INP_INFO_WLOCK_ASSERT(ipi)	rw_assert(&(ipi)->ipi_lock, RA_WLOCKED)
 #define INP_INFO_UNLOCK_ASSERT(ipi)	rw_assert(&(ipi)->ipi_lock, RA_UNLOCKED)
 
+#define INP_LIST_LOCK_INIT(ipi, d) \
+        rw_init_flags(&(ipi)->ipi_list_lock, (d), 0)
+#define INP_LIST_LOCK_DESTROY(ipi)  rw_destroy(&(ipi)->ipi_list_lock)
+#define INP_LIST_RLOCK(ipi)     rw_rlock(&(ipi)->ipi_list_lock)
+#define INP_LIST_WLOCK(ipi)     rw_wlock(&(ipi)->ipi_list_lock)
+#define INP_LIST_TRY_RLOCK(ipi) rw_try_rlock(&(ipi)->ipi_list_lock)
+#define INP_LIST_TRY_WLOCK(ipi) rw_try_wlock(&(ipi)->ipi_list_lock)
+#define INP_LIST_TRY_UPGRADE(ipi)       rw_try_upgrade(&(ipi)->ipi_list_lock)
+#define INP_LIST_RUNLOCK(ipi)   rw_runlock(&(ipi)->ipi_list_lock)
+#define INP_LIST_WUNLOCK(ipi)   rw_wunlock(&(ipi)->ipi_list_lock)
+#define INP_LIST_LOCK_ASSERT(ipi) \
+	rw_assert(&(ipi)->ipi_list_lock, RA_LOCKED)
+#define INP_LIST_RLOCK_ASSERT(ipi) \
+	rw_assert(&(ipi)->ipi_list_lock, RA_RLOCKED)
+#define INP_LIST_WLOCK_ASSERT(ipi) \
+	rw_assert(&(ipi)->ipi_list_lock, RA_WLOCKED)
+#define INP_LIST_UNLOCK_ASSERT(ipi) \
+	rw_assert(&(ipi)->ipi_list_lock, RA_UNLOCKED)
+
 #define	INP_HASH_LOCK_INIT(ipi, d) \
 	rw_init_flags(&(ipi)->ipi_hash_lock, (d), 0)
 #define	INP_HASH_LOCK_DESTROY(ipi)	rw_destroy(&(ipi)->ipi_hash_lock)
diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index 3ca37b549129..e7ef6dbb80d8 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -608,7 +608,7 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
 	char *s = NULL;			/* address and port logging */
 	int ti_locked;
 #define	TI_UNLOCKED	1
-#define	TI_WLOCKED	2
+#define	TI_RLOCKED	2
 
 #ifdef TCPDEBUG
 	/*
@@ -797,8 +797,8 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
 	 * connection in TIMEWAIT and SYNs not targeting a listening socket.
 	 */
 	if ((thflags & (TH_FIN | TH_RST)) != 0) {
-		INP_INFO_WLOCK(&V_tcbinfo);
-		ti_locked = TI_WLOCKED;
+		INP_INFO_RLOCK(&V_tcbinfo);
+		ti_locked = TI_RLOCKED;
 	} else
 		ti_locked = TI_UNLOCKED;
 
@@ -820,8 +820,8 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
 
 findpcb:
 #ifdef INVARIANTS
-	if (ti_locked == TI_WLOCKED) {
-		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	if (ti_locked == TI_RLOCKED) {
+		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	} else {
 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 	}
@@ -969,20 +969,20 @@ findpcb:
 relocked:
 	if (inp->inp_flags & INP_TIMEWAIT) {
 		if (ti_locked == TI_UNLOCKED) {
-			if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
+			if (INP_INFO_TRY_RLOCK(&V_tcbinfo) == 0) {
 				in_pcbref(inp);
 				INP_WUNLOCK(inp);
-				INP_INFO_WLOCK(&V_tcbinfo);
-				ti_locked = TI_WLOCKED;
+				INP_INFO_RLOCK(&V_tcbinfo);
+				ti_locked = TI_RLOCKED;
 				INP_WLOCK(inp);
 				if (in_pcbrele_wlocked(inp)) {
 					inp = NULL;
 					goto findpcb;
 				}
 			} else
-				ti_locked = TI_WLOCKED;
+				ti_locked = TI_RLOCKED;
 		}
-		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 
 		if (thflags & TH_SYN)
 			tcp_dooptions(&to, optp, optlen, TO_SYN);
@@ -991,7 +991,7 @@ relocked:
 		 */
 		if (tcp_twcheck(inp, &to, th, m, tlen))
 			goto findpcb;
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		return (IPPROTO_DONE);
 	}
 	/*
@@ -1022,16 +1022,16 @@ relocked:
 	 */
 #ifdef INVARIANTS
 	if ((thflags & (TH_FIN | TH_RST)) != 0)
-		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 #endif
 	if (!((tp->t_state == TCPS_ESTABLISHED && (thflags & TH_SYN) == 0) ||
 	    (tp->t_state == TCPS_LISTEN && (thflags & TH_SYN)))) {
 		if (ti_locked == TI_UNLOCKED) {
-			if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
+			if (INP_INFO_TRY_RLOCK(&V_tcbinfo) == 0) {
 				in_pcbref(inp);
 				INP_WUNLOCK(inp);
-				INP_INFO_WLOCK(&V_tcbinfo);
-				ti_locked = TI_WLOCKED;
+				INP_INFO_RLOCK(&V_tcbinfo);
+				ti_locked = TI_RLOCKED;
 				INP_WLOCK(inp);
 				if (in_pcbrele_wlocked(inp)) {
 					inp = NULL;
@@ -1039,9 +1039,9 @@ relocked:
 				}
 				goto relocked;
 			} else
-				ti_locked = TI_WLOCKED;
+				ti_locked = TI_RLOCKED;
 		}
-		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	}
 
 #ifdef MAC
@@ -1096,7 +1096,7 @@ relocked:
 		 */
 		if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 
-			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 			/*
 			 * Parse the TCP options here because
 			 * syncookies need access to the reflected
@@ -1148,7 +1148,11 @@ relocked:
 			 */
 			INP_WUNLOCK(inp);	/* listen socket */
 			inp = sotoinpcb(so);
-			INP_WLOCK(inp);		/* new connection */
+			/*
+			 * New connection inpcb is already locked by
+			 * syncache_expand().
+			 */
+			INP_WLOCK_ASSERT(inp);
 			tp = intotcpcb(inp);
 			KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
 			    ("%s: ", __func__));
@@ -1379,8 +1383,8 @@ relocked:
 		 * Entry added to syncache and mbuf consumed.
 		 * Only the listen socket is unlocked by syncache_add().
 		 */
-		if (ti_locked == TI_WLOCKED) {
-			INP_INFO_WUNLOCK(&V_tcbinfo);
+		if (ti_locked == TI_RLOCKED) {
+			INP_INFO_RUNLOCK(&V_tcbinfo);
 			ti_locked = TI_UNLOCKED;
 		}
 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
@@ -1429,8 +1433,8 @@ relocked:
 dropwithreset:
 	TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 
-	if (ti_locked == TI_WLOCKED) {
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+	if (ti_locked == TI_RLOCKED) {
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		ti_locked = TI_UNLOCKED;
 	}
 #ifdef INVARIANTS
@@ -1453,8 +1457,8 @@ dropunlock:
 	if (m != NULL)
 		TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 
-	if (ti_locked == TI_WLOCKED) {
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+	if (ti_locked == TI_RLOCKED) {
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		ti_locked = TI_UNLOCKED;
 	}
 #ifdef INVARIANTS
@@ -1511,13 +1515,13 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 	 */
 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
 	    tp->t_state != TCPS_ESTABLISHED) {
-		KASSERT(ti_locked == TI_WLOCKED, ("%s ti_locked %d for "
+		KASSERT(ti_locked == TI_RLOCKED, ("%s ti_locked %d for "
 		    "SYN/FIN/RST/!EST", __func__, ti_locked));
-		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	} else {
 #ifdef INVARIANTS
-		if (ti_locked == TI_WLOCKED)
-			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+		if (ti_locked == TI_RLOCKED)
+			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 		else {
 			KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
 			    "ti_locked: %d", __func__, ti_locked));
@@ -1690,8 +1694,8 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 				/*
 				 * This is a pure ack for outstanding data.
 				 */
-				if (ti_locked == TI_WLOCKED)
-					INP_INFO_WUNLOCK(&V_tcbinfo);
+				if (ti_locked == TI_RLOCKED)
+					INP_INFO_RUNLOCK(&V_tcbinfo);
 				ti_locked = TI_UNLOCKED;
 
 				TCPSTAT_INC(tcps_predack);
@@ -1794,8 +1798,8 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 			 * nothing on the reassembly queue and we have enough
 			 * buffer space to take it.
 			 */
-			if (ti_locked == TI_WLOCKED)
-				INP_INFO_WUNLOCK(&V_tcbinfo);
+			if (ti_locked == TI_RLOCKED)
+				INP_INFO_RUNLOCK(&V_tcbinfo);
 			ti_locked = TI_UNLOCKED;
 
 			/* Clean receiver SACK report if present */
@@ -2031,9 +2035,9 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 			tcp_state_change(tp, TCPS_SYN_RECEIVED);
 		}
 
-		KASSERT(ti_locked == TI_WLOCKED, ("%s: trimthenstep6: "
+		KASSERT(ti_locked == TI_RLOCKED, ("%s: trimthenstep6: "
 		    "ti_locked %d", __func__, ti_locked));
-		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 		INP_WLOCK_ASSERT(tp->t_inpcb);
 
 		/*
@@ -2106,8 +2110,8 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 		    SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) ||
 		    (tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
 
-			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
-			KASSERT(ti_locked == TI_WLOCKED,
+			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
+			KASSERT(ti_locked == TI_RLOCKED,
 			    ("%s: TH_RST ti_locked %d, th %p tp %p",
 			    __func__, ti_locked, th, tp));
 			KASSERT(tp->t_state != TCPS_SYN_SENT,
@@ -2150,9 +2154,9 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 	 * Send challenge ACK for any SYN in synchronized state.
 	 */
 	if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT) {
-		KASSERT(ti_locked == TI_WLOCKED,
+		KASSERT(ti_locked == TI_RLOCKED,
 		    ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
-		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 
 		TCPSTAT_INC(tcps_badsyn);
 		if (V_tcp_insecure_syn &&
@@ -2265,9 +2269,9 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 	 */
 	if ((so->so_state & SS_NOFDREF) &&
 	    tp->t_state > TCPS_CLOSE_WAIT && tlen) {
-		KASSERT(ti_locked == TI_WLOCKED, ("%s: SS_NOFDEREF && "
+		KASSERT(ti_locked == TI_RLOCKED, ("%s: SS_NOFDEREF && "
 		    "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
-		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 
 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 			log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
@@ -2768,9 +2772,9 @@ process_ACK:
 		 */
 		case TCPS_CLOSING:
 			if (ourfinisacked) {
-				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 				tcp_twstart(tp);
-				INP_INFO_WUNLOCK(&V_tcbinfo);
+				INP_INFO_RUNLOCK(&V_tcbinfo);
 				m_freem(m);
 				return;
 			}
@@ -2784,7 +2788,7 @@ process_ACK:
 		 */
 		case TCPS_LAST_ACK:
 			if (ourfinisacked) {
-				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 				tp = tcp_close(tp);
 				goto drop;
 			}
@@ -2999,18 +3003,18 @@ dodata:							/* XXX */
 		 * standard timers.
 		 */
 		case TCPS_FIN_WAIT_2:
-			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
-			KASSERT(ti_locked == TI_WLOCKED, ("%s: dodata "
+			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
+			KASSERT(ti_locked == TI_RLOCKED, ("%s: dodata "
 			    "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
 			    ti_locked));
 
 			tcp_twstart(tp);
-			INP_INFO_WUNLOCK(&V_tcbinfo);
+			INP_INFO_RUNLOCK(&V_tcbinfo);
 			return;
 		}
 	}
-	if (ti_locked == TI_WLOCKED)
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+	if (ti_locked == TI_RLOCKED)
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 	ti_locked = TI_UNLOCKED;
 
 #ifdef TCPDEBUG
@@ -3065,8 +3069,8 @@ dropafterack:
 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 			  &tcp_savetcp, 0);
 #endif
-	if (ti_locked == TI_WLOCKED)
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+	if (ti_locked == TI_RLOCKED)
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 	ti_locked = TI_UNLOCKED;
 
 	tp->t_flags |= TF_ACKNOW;
@@ -3076,8 +3080,8 @@ dropafterack:
 	return;
 
 dropwithreset:
-	if (ti_locked == TI_WLOCKED)
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+	if (ti_locked == TI_RLOCKED)
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 	ti_locked = TI_UNLOCKED;
 
 	if (tp != NULL) {
@@ -3088,8 +3092,8 @@ dropwithreset:
 	return;
 
 drop:
-	if (ti_locked == TI_WLOCKED) {
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+	if (ti_locked == TI_RLOCKED) {
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		ti_locked = TI_UNLOCKED;
 	}
 #ifdef INVARIANTS
diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index 7fe0eba0a310..808eb9736f7c 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -858,7 +858,7 @@ tcp_ccalgounload(struct cc_algo *unload_algo)
 	VNET_LIST_RLOCK();
 	VNET_FOREACH(vnet_iter) {
 		CURVNET_SET(vnet_iter);
-		INP_INFO_RLOCK(&V_tcbinfo);
+		INP_INFO_WLOCK(&V_tcbinfo);
 		/*
 		 * New connections already part way through being initialised
 		 * with the CC algo we're removing will not race with this code
@@ -888,7 +888,7 @@ tcp_ccalgounload(struct cc_algo *unload_algo)
 			}
 			INP_WUNLOCK(inp);
 		}
-		INP_INFO_RUNLOCK(&V_tcbinfo);
+		INP_INFO_WUNLOCK(&V_tcbinfo);
 		CURVNET_RESTORE();
 	}
 	VNET_LIST_RUNLOCK();
@@ -906,7 +906,7 @@ tcp_drop(struct tcpcb *tp, int errno)
 {
 	struct socket *so = tp->t_inpcb->inp_socket;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(tp->t_inpcb);
 
 	if (TCPS_HAVERCVDSYN(tp->t_state)) {
@@ -1073,7 +1073,7 @@ tcp_timer_discard(struct tcpcb *tp, uint32_t timer_type)
 	struct inpcb *inp;
 
 	CURVNET_SET(tp->t_vnet);
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	inp = tp->t_inpcb;
 	KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL",
 		__func__, tp));
@@ -1088,13 +1088,13 @@ tcp_timer_discard(struct tcpcb *tp, uint32_t timer_type)
 		tp->t_inpcb = NULL;
 		uma_zfree(V_tcpcb_zone, tp);
 		if (in_pcbrele_wlocked(inp)) {
-			INP_INFO_WUNLOCK(&V_tcbinfo);
+			INP_INFO_RUNLOCK(&V_tcbinfo);
 			CURVNET_RESTORE();
 			return;
 		}
 	}
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	CURVNET_RESTORE();
 }
 
@@ -1108,7 +1108,7 @@ tcp_close(struct tcpcb *tp)
 	struct inpcb *inp = tp->t_inpcb;
 	struct socket *so;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(inp);
 
 #ifdef TCP_OFFLOAD
@@ -1156,7 +1156,7 @@ tcp_drain(void)
 	 *	where we're really low on mbufs, this is potentially
 	 *	useful.
 	 */
-		INP_INFO_RLOCK(&V_tcbinfo);
+		INP_INFO_WLOCK(&V_tcbinfo);
 		LIST_FOREACH(inpb, V_tcbinfo.ipi_listhead, inp_list) {
 			if (inpb->inp_flags & INP_TIMEWAIT)
 				continue;
@@ -1167,7 +1167,7 @@ tcp_drain(void)
 			}
 			INP_WUNLOCK(inpb);
 		}
-		INP_INFO_RUNLOCK(&V_tcbinfo);
+		INP_INFO_WUNLOCK(&V_tcbinfo);
 		CURVNET_RESTORE();
 	}
 	VNET_LIST_RUNLOCK_NOSLEEP();
@@ -1186,7 +1186,7 @@ tcp_notify(struct inpcb *inp, int error)
 {
 	struct tcpcb *tp;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(inp);
 
 	if ((inp->inp_flags & INP_TIMEWAIT) ||
@@ -1250,10 +1250,10 @@ tcp_pcblist(SYSCTL_HANDLER_ARGS)
 	/*
 	 * OK, now we're committed to doing something.
 	 */
-	INP_INFO_RLOCK(&V_tcbinfo);
+	INP_LIST_RLOCK(&V_tcbinfo);
 	gencnt = V_tcbinfo.ipi_gencnt;
 	n = V_tcbinfo.ipi_count;
-	INP_INFO_RUNLOCK(&V_tcbinfo);
+	INP_LIST_RUNLOCK(&V_tcbinfo);
 
 	m = syncache_pcbcount();
 
@@ -1278,7 +1278,7 @@ tcp_pcblist(SYSCTL_HANDLER_ARGS)
 	if (inp_list == NULL)
 		return (ENOMEM);
 
-	INP_INFO_RLOCK(&V_tcbinfo);
+	INP_INFO_WLOCK(&V_tcbinfo);
 	for (inp = LIST_FIRST(V_tcbinfo.ipi_listhead), i = 0;
 	    inp != NULL && i < n; inp = LIST_NEXT(inp, inp_list)) {
 		INP_WLOCK(inp);
@@ -1303,7 +1303,7 @@ tcp_pcblist(SYSCTL_HANDLER_ARGS)
 		}
 		INP_WUNLOCK(inp);
 	}
-	INP_INFO_RUNLOCK(&V_tcbinfo);
+	INP_INFO_WUNLOCK(&V_tcbinfo);
 	n = i;
 
 	error = 0;
@@ -1341,14 +1341,14 @@ tcp_pcblist(SYSCTL_HANDLER_ARGS)
 		} else
 			INP_RUNLOCK(inp);
 	}
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	for (i = 0; i < n; i++) {
 		inp = inp_list[i];
 		INP_RLOCK(inp);
 		if (!in_pcbrele_rlocked(inp))
 			INP_RUNLOCK(inp);
 	}
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 
 	if (!error) {
 		/*
@@ -1358,11 +1358,11 @@ tcp_pcblist(SYSCTL_HANDLER_ARGS)
 		 * while we were processing this request, and it
 		 * might be necessary to retry.
 		 */
-		INP_INFO_RLOCK(&V_tcbinfo);
+		INP_LIST_RLOCK(&V_tcbinfo);
 		xig.xig_gen = V_tcbinfo.ipi_gencnt;
 		xig.xig_sogen = so_gencnt;
 		xig.xig_count = V_tcbinfo.ipi_count + pcb_count;
-		INP_INFO_RUNLOCK(&V_tcbinfo);
+		INP_LIST_RUNLOCK(&V_tcbinfo);
 		error = SYSCTL_OUT(req, &xig, sizeof xig);
 	}
 	free(inp_list, M_TEMP);
@@ -1518,7 +1518,7 @@ tcp_ctlinput(int cmd, struct sockaddr *sa, void *vip)
 				      - offsetof(struct icmp, icmp_ip));
 		th = (struct tcphdr *)((caddr_t)ip
 				       + (ip->ip_hl << 2));
-		INP_INFO_WLOCK(&V_tcbinfo);
+		INP_INFO_RLOCK(&V_tcbinfo);
 		inp = in_pcblookup(&V_tcbinfo, faddr, th->th_dport,
 		    ip->ip_src, th->th_sport, INPLOOKUP_WLOCKPCB, NULL);
 		if (inp != NULL)  {
@@ -1578,7 +1578,7 @@ tcp_ctlinput(int cmd, struct sockaddr *sa, void *vip)
 			inc.inc_laddr = ip->ip_src;
 			syncache_unreach(&inc, th);
 		}
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 	} else
 		in_pcbnotifyall(&V_tcbinfo, faddr, inetctlerrmap[cmd], notify);
 }
@@ -1648,9 +1648,9 @@ tcp6_ctlinput(int cmd, struct sockaddr *sa, void *d)
 		inc.inc6_faddr = ((struct sockaddr_in6 *)sa)->sin6_addr;
 		inc.inc6_laddr = ip6cp->ip6c_src->sin6_addr;
 		inc.inc_flags |= INC_ISIPV6;
-		INP_INFO_WLOCK(&V_tcbinfo);
+		INP_INFO_RLOCK(&V_tcbinfo);
 		syncache_unreach(&inc, &th);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 	} else
 		in6_pcbnotify(&V_tcbinfo, sa, 0, (const struct sockaddr *)sa6_src,
 			      0, cmd, NULL, notify);
@@ -1783,7 +1783,7 @@ tcp_drop_syn_sent(struct inpcb *inp, int errno)
 {
 	struct tcpcb *tp;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(inp);
 
 	if ((inp->inp_flags & INP_TIMEWAIT) ||
@@ -2341,7 +2341,7 @@ sysctl_drop(SYSCTL_HANDLER_ARGS)
 	default:
 		return (EINVAL);
 	}
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	switch (addrs[0].ss_family) {
 #ifdef INET6
 	case AF_INET6:
@@ -2380,7 +2380,7 @@ sysctl_drop(SYSCTL_HANDLER_ARGS)
 			INP_WUNLOCK(inp);
 	} else
 		error = ESRCH;
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	return (error);
 }
 
diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c
index 7d97ae081a6b..2c853b3b55e2 100644
--- a/sys/netinet/tcp_syncache.c
+++ b/sys/netinet/tcp_syncache.c
@@ -652,6 +652,8 @@ done:
 
 /*
  * Build a new TCP socket structure from a syncache entry.
+ *
+ * On success return the newly created socket with its underlying inp locked.
  */
 static struct socket *
 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
@@ -662,7 +664,7 @@ syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
 	int error;
 	char *s;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 
 	/*
 	 * Ok, create the full blown connection, and set things up
@@ -693,6 +695,15 @@ syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
 	inp = sotoinpcb(so);
 	inp->inp_inc.inc_fibnum = so->so_fibnum;
 	INP_WLOCK(inp);
+	/*
+	 * Exclusive pcbinfo lock is not required in syncache socket case even
+	 * if two inpcb locks can be acquired simultaneously:
+	 *  - the inpcb in LISTEN state,
+	 *  - the newly created inp.
+	 *
+	 * In this case, an inp cannot be at same time in LISTEN state and
+	 * just created by an accept() call.
+	 */
 	INP_HASH_WLOCK(&V_tcbinfo);
 
 	/* Insert new socket into PCB hash list. */
@@ -907,8 +918,6 @@ syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
 	tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
 	tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
 
-	INP_WUNLOCK(inp);
-
 	soisconnected(so);
 
 	TCPSTAT_INC(tcps_accepts);
@@ -928,6 +937,9 @@ abort2:
  * in the syncache, and if its there, we pull it out of
  * the cache and turn it into a full-blown connection in
  * the SYN-RECEIVED state.
+ *
+ * On syncache_socket() success the newly created socket
+ * has its underlying inp locked.
  */
 int
 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
@@ -942,7 +954,7 @@ syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 	 * Global TCP locks are held because we manipulate the PCB lists
 	 * and create a new socket.
 	 */
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
 	    ("%s: can handle only ACK", __func__));
 
diff --git a/sys/netinet/tcp_timer.c b/sys/netinet/tcp_timer.c
index d992492cddc7..e0073346a548 100644
--- a/sys/netinet/tcp_timer.c
+++ b/sys/netinet/tcp_timer.c
@@ -307,7 +307,7 @@ tcp_timer_2msl(void *xtp)
 
 	ostate = tp->t_state;
 #endif
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	inp = tp->t_inpcb;
 	KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
 	INP_WLOCK(inp);
@@ -315,14 +315,14 @@ tcp_timer_2msl(void *xtp)
 	if (callout_pending(&tp->t_timers->tt_2msl) ||
 	    !callout_active(&tp->t_timers->tt_2msl)) {
 		INP_WUNLOCK(tp->t_inpcb);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		CURVNET_RESTORE();
 		return;
 	}
 	callout_deactivate(&tp->t_timers->tt_2msl);
 	if ((inp->inp_flags & INP_DROPPED) != 0) {
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		CURVNET_RESTORE();
 		return;
 	}
@@ -363,7 +363,7 @@ tcp_timer_2msl(void *xtp)
 #endif
 	if (tp != NULL)
 		INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	CURVNET_RESTORE();
 }
 
@@ -379,21 +379,21 @@ tcp_timer_keep(void *xtp)
 
 	ostate = tp->t_state;
 #endif
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	inp = tp->t_inpcb;
 	KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
 	INP_WLOCK(inp);
 	if (callout_pending(&tp->t_timers->tt_keep) ||
 	    !callout_active(&tp->t_timers->tt_keep)) {
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		CURVNET_RESTORE();
 		return;
 	}
 	callout_deactivate(&tp->t_timers->tt_keep);
 	if ((inp->inp_flags & INP_DROPPED) != 0) {
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		CURVNET_RESTORE();
 		return;
 	}
@@ -447,7 +447,7 @@ tcp_timer_keep(void *xtp)
 			  PRU_SLOWTIMO);
 #endif
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	CURVNET_RESTORE();
 	return;
 
@@ -462,7 +462,7 @@ dropit:
 #endif
 	if (tp != NULL)
 		INP_WUNLOCK(tp->t_inpcb);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	CURVNET_RESTORE();
 }
 
@@ -477,21 +477,21 @@ tcp_timer_persist(void *xtp)
 
 	ostate = tp->t_state;
 #endif
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	inp = tp->t_inpcb;
 	KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
 	INP_WLOCK(inp);
 	if (callout_pending(&tp->t_timers->tt_persist) ||
 	    !callout_active(&tp->t_timers->tt_persist)) {
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		CURVNET_RESTORE();
 		return;
 	}
 	callout_deactivate(&tp->t_timers->tt_persist);
 	if ((inp->inp_flags & INP_DROPPED) != 0) {
 		INP_WUNLOCK(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		CURVNET_RESTORE();
 		return;
 	}
@@ -540,7 +540,7 @@ out:
 #endif
 	if (tp != NULL)
 		INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	CURVNET_RESTORE();
 }
 
@@ -589,22 +589,6 @@ tcp_timer_rexmt(void * xtp)
 	if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 		tp->t_rxtshift = TCP_MAXRXTSHIFT;
 		TCPSTAT_INC(tcps_timeoutdrop);
-		in_pcbref(inp);
-		INP_INFO_RUNLOCK(&V_tcbinfo);
-		INP_WUNLOCK(inp);
-		INP_INFO_WLOCK(&V_tcbinfo);
-		INP_WLOCK(inp);
-		if (in_pcbrele_wlocked(inp)) {
-			INP_INFO_WUNLOCK(&V_tcbinfo);
-			CURVNET_RESTORE();
-			return;
-		}
-		if (inp->inp_flags & INP_DROPPED) {
-			INP_WUNLOCK(inp);
-			INP_INFO_WUNLOCK(&V_tcbinfo);
-			CURVNET_RESTORE();
-			return;
-		}
 
 		tp = tcp_drop(tp, tp->t_softerror ?
 			      tp->t_softerror : ETIMEDOUT);
@@ -803,7 +787,7 @@ out:
 	if (tp != NULL)
 		INP_WUNLOCK(inp);
 	if (headlocked)
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 	CURVNET_RESTORE();
 }
 
diff --git a/sys/netinet/tcp_timewait.c b/sys/netinet/tcp_timewait.c
index 1ba74d86ae68..4685fe734f5e 100644
--- a/sys/netinet/tcp_timewait.c
+++ b/sys/netinet/tcp_timewait.c
@@ -202,10 +202,10 @@ tcp_tw_destroy(void)
 {
 	struct tcptw *tw;
 
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	while ((tw = TAILQ_FIRST(&V_twq_2msl)) != NULL)
 		tcp_twclose(tw, 0);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 
 	TW_LOCK_DESTROY(V_tw_lock);
 	uma_zdestroy(V_tcptw_zone);
@@ -228,7 +228,7 @@ tcp_twstart(struct tcpcb *tp)
 	int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
 #endif
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(inp);
 
 	if (V_nolocaltimewait) {
@@ -265,8 +265,8 @@ tcp_twstart(struct tcpcb *tp)
 		 * allowed. Remove a connection from TIMEWAIT queue in LRU
 		 * fashion to make room for this connection.
 		 *
-		 * pcbinfo lock is needed here to prevent deadlock as
-		 * two inpcb locks can be acquired simultaneously.
+		 * XXX:  Check if it possible to always have enough room
+		 * in advance based on guarantees provided by uma_zalloc().
 		 */
 		tw = tcp_tw_2msl_scan(1);
 		if (tw == NULL) {
@@ -367,7 +367,7 @@ tcp_twcheck(struct inpcb *inp, struct tcpopt *to __unused, struct tcphdr *th,
 	int thflags;
 	tcp_seq seq;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(inp);
 
 	/*
@@ -468,7 +468,7 @@ tcp_twclose(struct tcptw *tw, int reuse)
 	inp = tw->tw_inpcb;
 	KASSERT((inp->inp_flags & INP_TIMEWAIT), ("tcp_twclose: !timewait"));
 	KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw"));
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);	/* in_pcbfree() */
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);	/* in_pcbfree() */
 	INP_WLOCK_ASSERT(inp);
 
 	tcp_tw_2msl_stop(tw, reuse);
@@ -623,7 +623,7 @@ static void
 tcp_tw_2msl_reset(struct tcptw *tw, int rearm)
 {
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(tw->tw_inpcb);
 
 	TW_WLOCK(V_tw_lock);
@@ -641,7 +641,7 @@ tcp_tw_2msl_stop(struct tcptw *tw, int reuse)
 	struct inpcb *inp;
 	int released;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 
 	TW_WLOCK(V_tw_lock);
 	inp = tw->tw_inpcb;
@@ -671,13 +671,18 @@ tcp_tw_2msl_scan(int reuse)
 #ifdef INVARIANTS
 	if (reuse) {
 		/*
-		 * pcbinfo lock is needed in reuse case to prevent deadlock
-		 * as two inpcb locks can be acquired simultaneously:
+		 * Exclusive pcbinfo lock is not required in reuse case even if
+		 * two inpcb locks can be acquired simultaneously:
 		 *  - the inpcb transitioning to TIME_WAIT state in
 		 *    tcp_tw_start(),
 		 *  - the inpcb closed by tcp_twclose().
+		 *
+		 * It is because only inpcbs in FIN_WAIT2 or CLOSING states can
+		 * transition in TIME_WAIT state.  Then a pcbcb cannot be in
+		 * TIME_WAIT list and transitioning to TIME_WAIT state at same
+		 * time.
 		 */
-		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	}
 #endif
 
@@ -695,26 +700,26 @@ tcp_tw_2msl_scan(int reuse)
 		in_pcbref(inp);
 		TW_RUNLOCK(V_tw_lock);
 
-		if (INP_INFO_TRY_WLOCK(&V_tcbinfo)) {
+		if (INP_INFO_TRY_RLOCK(&V_tcbinfo)) {
 
 			INP_WLOCK(inp);
 			tw = intotw(inp);
 			if (in_pcbrele_wlocked(inp)) {
 				KASSERT(tw == NULL, ("%s: held last inp "
 				    "reference but tw not NULL", __func__));
-				INP_INFO_WUNLOCK(&V_tcbinfo);
+				INP_INFO_RUNLOCK(&V_tcbinfo);
 				continue;
 			}
 
 			if (tw == NULL) {
 				/* tcp_twclose() has already been called */
 				INP_WUNLOCK(inp);
-				INP_INFO_WUNLOCK(&V_tcbinfo);
+				INP_INFO_RUNLOCK(&V_tcbinfo);
 				continue;
 			}
 
 			tcp_twclose(tw, reuse);
-			INP_INFO_WUNLOCK(&V_tcbinfo);
+			INP_INFO_RUNLOCK(&V_tcbinfo);
 			if (reuse)
 			    return tw;
 		} else {
diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c
index de2de94e18e1..36d5312aec26 100644
--- a/sys/netinet/tcp_usrreq.c
+++ b/sys/netinet/tcp_usrreq.c
@@ -163,7 +163,7 @@ tcp_detach(struct socket *so, struct inpcb *inp)
 {
 	struct tcpcb *tp;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(inp);
 
 	KASSERT(so->so_pcb == inp, ("tcp_detach: so_pcb != inp"));
@@ -192,10 +192,10 @@ tcp_detach(struct socket *so, struct inpcb *inp)
 		 *  and leave inpcb present until timewait ends
 		 * #2 tcp_detach is called at timewait end (or reuse) by
 		 *  tcp_twclose, then the tcptw has already been discarded
-		 *  and inpcb is freed here
+		 *  (or reused) and inpcb is freed here
 		 * #3 tcp_detach is called() after timewait ends (or reuse)
 		 *  (e.g. by soclose), then tcptw has already been discarded
-		 *  and inpcb is freed here
+		 *  (or reused) and inpcb is freed here
 		 *
 		 *  In all three cases the tcptw should not be freed here.
 		 */
@@ -244,12 +244,12 @@ tcp_usr_detach(struct socket *so)
 
 	inp = sotoinpcb(so);
 	KASSERT(inp != NULL, ("tcp_usr_detach: inp == NULL"));
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	KASSERT(inp->inp_socket != NULL,
 	    ("tcp_usr_detach: inp_socket == NULL"));
 	tcp_detach(so, inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 }
 
 #ifdef INET
@@ -611,7 +611,7 @@ tcp_usr_disconnect(struct socket *so)
 	int error = 0;
 
 	TCPDEBUG0;
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	inp = sotoinpcb(so);
 	KASSERT(inp != NULL, ("tcp_usr_disconnect: inp == NULL"));
 	INP_WLOCK(inp);
@@ -627,7 +627,7 @@ tcp_usr_disconnect(struct socket *so)
 out:
 	TCPDEBUG2(PRU_DISCONNECT);
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	return (error);
 }
 
@@ -742,7 +742,7 @@ tcp_usr_shutdown(struct socket *so)
 	struct tcpcb *tp = NULL;
 
 	TCPDEBUG0;
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	inp = sotoinpcb(so);
 	KASSERT(inp != NULL, ("inp == NULL"));
 	INP_WLOCK(inp);
@@ -760,7 +760,7 @@ tcp_usr_shutdown(struct socket *so)
 out:
 	TCPDEBUG2(PRU_SHUTDOWN);
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 
 	return (error);
 }
@@ -822,7 +822,7 @@ tcp_usr_send(struct socket *so, int flags, struct mbuf *m,
 	 * this call.
 	 */
 	if (flags & PRUS_EOF)
-		INP_INFO_WLOCK(&V_tcbinfo);
+		INP_INFO_RLOCK(&V_tcbinfo);
 	inp = sotoinpcb(so);
 	KASSERT(inp != NULL, ("tcp_usr_send: inp == NULL"));
 	INP_WLOCK(inp);
@@ -883,7 +883,7 @@ tcp_usr_send(struct socket *so, int flags, struct mbuf *m,
 			 * Close the send side of the connection after
 			 * the data is sent.
 			 */
-			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 			socantsendmore(so);
 			tcp_usrclosed(tp);
 		}
@@ -950,7 +950,7 @@ out:
 		  ((flags & PRUS_EOF) ? PRU_SEND_EOF : PRU_SEND));
 	INP_WUNLOCK(inp);
 	if (flags & PRUS_EOF)
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 	return (error);
 }
 
@@ -994,7 +994,7 @@ tcp_usr_abort(struct socket *so)
 	inp = sotoinpcb(so);
 	KASSERT(inp != NULL, ("tcp_usr_abort: inp == NULL"));
 
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	KASSERT(inp->inp_socket != NULL,
 	    ("tcp_usr_abort: inp_socket == NULL"));
@@ -1016,7 +1016,7 @@ tcp_usr_abort(struct socket *so)
 		inp->inp_flags |= INP_SOCKREF;
 	}
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 }
 
 /*
@@ -1032,7 +1032,7 @@ tcp_usr_close(struct socket *so)
 	inp = sotoinpcb(so);
 	KASSERT(inp != NULL, ("tcp_usr_close: inp == NULL"));
 
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	KASSERT(inp->inp_socket != NULL,
 	    ("tcp_usr_close: inp_socket == NULL"));
@@ -1055,7 +1055,7 @@ tcp_usr_close(struct socket *so)
 		inp->inp_flags |= INP_SOCKREF;
 	}
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 }
 
 /*
@@ -1655,10 +1655,10 @@ tcp_attach(struct socket *so)
 	}
 	so->so_rcv.sb_flags |= SB_AUTOSIZE;
 	so->so_snd.sb_flags |= SB_AUTOSIZE;
-	INP_INFO_WLOCK(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
 	error = in_pcballoc(so, &V_tcbinfo);
 	if (error) {
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		return (error);
 	}
 	inp = sotoinpcb(so);
@@ -1674,12 +1674,12 @@ tcp_attach(struct socket *so)
 	if (tp == NULL) {
 		in_pcbdetach(inp);
 		in_pcbfree(inp);
-		INP_INFO_WUNLOCK(&V_tcbinfo);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
 		return (ENOBUFS);
 	}
 	tp->t_state = TCPS_CLOSED;
 	INP_WUNLOCK(inp);
-	INP_INFO_WUNLOCK(&V_tcbinfo);
+	INP_INFO_RUNLOCK(&V_tcbinfo);
 	return (0);
 }
 
@@ -1697,7 +1697,7 @@ tcp_disconnect(struct tcpcb *tp)
 	struct inpcb *inp = tp->t_inpcb;
 	struct socket *so = inp->inp_socket;
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(inp);
 
 	/*
@@ -1735,7 +1735,7 @@ static void
 tcp_usrclosed(struct tcpcb *tp)
 {
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 	INP_WLOCK_ASSERT(tp->t_inpcb);
 
 	switch (tp->t_state) {
diff --git a/sys/netinet/toecore.c b/sys/netinet/toecore.c
index 1021475f9319..5ca460483537 100644
--- a/sys/netinet/toecore.c
+++ b/sys/netinet/toecore.c
@@ -339,7 +339,7 @@ toe_syncache_expand(struct in_conninfo *inc, struct tcpopt *to,
     struct tcphdr *th, struct socket **lsop)
 {
 
-	INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 
 	return (syncache_expand(inc, to, th, lsop, NULL));
 }
@@ -370,7 +370,7 @@ toe_4tuple_check(struct in_conninfo *inc, struct tcphdr *th, struct ifnet *ifp)
 
 		if ((inp->inp_flags & INP_TIMEWAIT) && th != NULL) {
 
-			INP_INFO_WLOCK_ASSERT(&V_tcbinfo); /* for twcheck */
+			INP_INFO_RLOCK_ASSERT(&V_tcbinfo); /* for twcheck */
 			if (!tcp_twcheck(inp, NULL, th, NULL, 0))
 				return (EADDRINUSE);
 		} else {
@@ -571,7 +571,7 @@ toe_connect_failed(struct toedev *tod, struct inpcb *inp, int err)
 			(void) tcp_output(tp);
 		} else {
 
-			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
+			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 			tp = tcp_drop(tp, err);
 			if (tp == NULL)
 				INP_WLOCK(inp);	/* re-acquire */
diff --git a/sys/netinet6/in6_pcb.c b/sys/netinet6/in6_pcb.c
index 10cd3f2b1bf0..9f876a4cbb92 100644
--- a/sys/netinet6/in6_pcb.c
+++ b/sys/netinet6/in6_pcb.c
@@ -789,7 +789,7 @@ in6_pcbpurgeif0(struct inpcbinfo *pcbinfo, struct ifnet *ifp)
 	struct ip6_moptions *im6o;
 	int i, gap;
 
-	INP_INFO_RLOCK(pcbinfo);
+	INP_INFO_WLOCK(pcbinfo);
 	LIST_FOREACH(in6p, pcbinfo->ipi_listhead, inp_list) {
 		INP_WLOCK(in6p);
 		im6o = in6p->in6p_moptions;
@@ -820,7 +820,7 @@ in6_pcbpurgeif0(struct inpcbinfo *pcbinfo, struct ifnet *ifp)
 		}
 		INP_WUNLOCK(in6p);
 	}
-	INP_INFO_RUNLOCK(pcbinfo);
+	INP_INFO_WUNLOCK(pcbinfo);
 }
 
 /*