tcp/dccp: remove twchain

TCP listener refactoring, part 3 :

Our goal is to hash SYN_RECV sockets into main ehash for fast lookup,
and parallel SYN processing.

Current inet_ehash_bucket contains two chains, one for ESTABLISH (and
friend states) sockets, another for TIME_WAIT sockets only.

As the hash table is sized to get at most one socket per bucket, it
makes little sense to have separate twchain, as it makes the lookup
slightly more complicated, and doubles hash table memory usage.

If we make sure all socket types have the lookup keys at the same
offsets, we can use a generic and faster lookup. It turns out TIME_WAIT
and ESTABLISHED sockets already have common lookup fields for IPv4.

[ INET_TW_MATCH() is no longer needed ]

I'll provide a follow-up to factorize IPv6 lookup as well, to remove
INET6_TW_MATCH()

This way, SYN_RECV pseudo sockets will be supported the same.

A new sock_gen_put() helper is added, doing either a sock_put() or
inet_twsk_put() [ and will support SYN_RECV later ].

Note this helper should only be called in real slow path, when rcu
lookup found a socket that was moved to another identity (freed/reused
immediately), but could eventually be used in other contexts, like
sock_edemux()

Before patch :

dmesg | grep "TCP established"

TCP established hash table entries: 524288 (order: 11, 8388608 bytes)

After patch :

TCP established hash table entries: 524288 (order: 10, 4194304 bytes)

Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/inet_hashtables.h

···
 #include <asm/byteorder.h>
 
 /* This is for all connections with a full identity, no wildcards.
- * One chain is dedicated to TIME_WAIT sockets.
- * I'll experiment with dynamic table growth later.
+ * The 'e' prefix stands for Establish, but we really put all sockets
+ * but LISTEN ones.
  */
 struct inet_ehash_bucket {
 	struct hlist_nulls_head chain;
-	struct hlist_nulls_head twchain;
 };
 
 /* There are a few simple rules, which allow for local port reuse by
···
 	 *
 	 *          TCP_ESTABLISHED <= sk->sk_state < TCP_CLOSE
 	 *
-	 * TIME_WAIT sockets use a separate chain (twchain).
 	 */
 	struct inet_ehash_bucket	*ehash;
 	spinlock_t			*ehash_locks;
···
 	   ((__sk)->sk_bound_dev_if == (__dif))) 	&&		\
 	 net_eq(sock_net(__sk), (__net)))
 #endif /* 64-bit arch */
-
-#define INET_TW_MATCH(__sk, __net, __cookie, __saddr, __daddr, __ports, __dif)\
-	INET_MATCH(__sk, __net, __cookie, __saddr, __daddr, __ports, __dif)
 
 /*
  * Sockets in TCP_CLOSE state are _always_ taken out of the hash, so we need

include/net/inet_timewait_sock.h

···
 };
 #define tw_tclass tw_tos
 
-static inline void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
-				      struct hlist_nulls_head *list)
-{
-	hlist_nulls_add_head_rcu(&tw->tw_node, list);
-}
-
-static inline void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
-					   struct hlist_head *list)
-{
-	hlist_add_head(&tw->tw_bind_node, list);
-}
-
 static inline int inet_twsk_dead_hashed(const struct inet_timewait_sock *tw)
 {
 	return !hlist_unhashed(&tw->tw_death_node);
···
 	return (struct inet_timewait_sock *)sk;
 }
 
+void inet_twsk_free(struct inet_timewait_sock *tw);
 void inet_twsk_put(struct inet_timewait_sock *tw);
 
 int inet_twsk_unhash(struct inet_timewait_sock *tw);

include/net/sock.h

···
  */
 struct sock_common {
 	/* skc_daddr and skc_rcv_saddr must be grouped on a 8 bytes aligned
-	 * address on 64bit arches : cf INET_MATCH() and INET_TW_MATCH()
+	 * address on 64bit arches : cf INET_MATCH()
 	 */
 	union {
 		__addrpair	skc_addrpair;
···
 #define sk_dontcopy_end		__sk_common.skc_dontcopy_end
 #define sk_hash			__sk_common.skc_hash
 #define sk_portpair		__sk_common.skc_portpair
+#define sk_num			__sk_common.skc_num
+#define sk_dport		__sk_common.skc_dport
 #define sk_addrpair		__sk_common.skc_addrpair
 #define sk_daddr		__sk_common.skc_daddr
 #define sk_rcv_saddr		__sk_common.skc_rcv_saddr
···
 	if (atomic_dec_and_test(&sk->sk_refcnt))
 		sk_free(sk);
 }
+/* Generic version of sock_put(), dealing with all sockets
+ * (TCP_TIMEWAIT, ESTABLISHED...)
+ */
+void sock_gen_put(struct sock *sk);
 
 int sk_receive_skb(struct sock *sk, struct sk_buff *skb, const int nested);
 

include/net/tcp.h

···
 	TCP_SEQ_STATE_LISTENING,
 	TCP_SEQ_STATE_OPENREQ,
 	TCP_SEQ_STATE_ESTABLISHED,
-	TCP_SEQ_STATE_TIME_WAIT,
 };
 
 int tcp_seq_open(struct inode *inode, struct file *file);

net/dccp/proto.c

···
 		goto out_free_bind_bucket_cachep;
 	}
 
-	for (i = 0; i <= dccp_hashinfo.ehash_mask; i++) {
+	for (i = 0; i <= dccp_hashinfo.ehash_mask; i++)
 		INIT_HLIST_NULLS_HEAD(&dccp_hashinfo.ehash[i].chain, i);
-		INIT_HLIST_NULLS_HEAD(&dccp_hashinfo.ehash[i].twchain, i);
-	}
 
 	if (inet_ehash_locks_alloc(&dccp_hashinfo))
 			goto out_free_dccp_ehash;

net/ipv4/inet_diag.c

···
 				  cb->nlh->nlmsg_seq, NLM_F_MULTI, cb->nlh);
 }
 
-static int inet_twsk_diag_dump(struct inet_timewait_sock *tw,
+static int inet_twsk_diag_dump(struct sock *sk,
 			       struct sk_buff *skb,
 			       struct netlink_callback *cb,
 			       struct inet_diag_req_v2 *r,
 			       const struct nlattr *bc)
 {
+	struct inet_timewait_sock *tw = inet_twsk(sk);
+
 	if (bc != NULL) {
 		struct inet_diag_entry entry;
 
···
 
 		num = 0;
 
-		if (hlist_nulls_empty(&head->chain) &&
-			hlist_nulls_empty(&head->twchain))
+		if (hlist_nulls_empty(&head->chain))
 			continue;
 
 		if (i > s_i)
···
 
 		spin_lock_bh(lock);
 		sk_nulls_for_each(sk, node, &head->chain) {
-			struct inet_sock *inet = inet_sk(sk);
+			int res;
 
 			if (!net_eq(sock_net(sk), net))
 				continue;
···
 			if (!(r->idiag_states & (1 << sk->sk_state)))
 				goto next_normal;
 			if (r->sdiag_family != AF_UNSPEC &&
-					sk->sk_family != r->sdiag_family)
+			    sk->sk_family != r->sdiag_family)
 				goto next_normal;
-			if (r->id.idiag_sport != inet->inet_sport &&
+			if (r->id.idiag_sport != htons(sk->sk_num) &&
 			    r->id.idiag_sport)
 				goto next_normal;
-			if (r->id.idiag_dport != inet->inet_dport &&
+			if (r->id.idiag_dport != sk->sk_dport &&
 			    r->id.idiag_dport)
 				goto next_normal;
-			if (inet_csk_diag_dump(sk, skb, cb, r, bc) < 0) {
+			if (sk->sk_state == TCP_TIME_WAIT)
+				res = inet_twsk_diag_dump(sk, skb, cb, r, bc);
+			else
+				res = inet_csk_diag_dump(sk, skb, cb, r, bc);
+			if (res < 0) {
 				spin_unlock_bh(lock);
 				goto done;
 			}
···
 			++num;
 		}
 
-		if (r->idiag_states & TCPF_TIME_WAIT) {
-			struct inet_timewait_sock *tw;
-
-			inet_twsk_for_each(tw, node,
-				    &head->twchain) {
-				if (!net_eq(twsk_net(tw), net))
-					continue;
-
-				if (num < s_num)
-					goto next_dying;
-				if (r->sdiag_family != AF_UNSPEC &&
-						tw->tw_family != r->sdiag_family)
-					goto next_dying;
-				if (r->id.idiag_sport != tw->tw_sport &&
-				    r->id.idiag_sport)
-					goto next_dying;
-				if (r->id.idiag_dport != tw->tw_dport &&
-				    r->id.idiag_dport)
-					goto next_dying;
-				if (inet_twsk_diag_dump(tw, skb, cb, r, bc) < 0) {
-					spin_unlock_bh(lock);
-					goto done;
-				}
-next_dying:
-				++num;
-			}
-		}
 		spin_unlock_bh(lock);
 	}
 

net/ipv4/inet_hashtables.c

···
 }
 EXPORT_SYMBOL_GPL(__inet_lookup_listener);
 
+/* All sockets share common refcount, but have different destructors */
+void sock_gen_put(struct sock *sk)
+{
+	if (!atomic_dec_and_test(&sk->sk_refcnt))
+		return;
+
+	if (sk->sk_state == TCP_TIME_WAIT)
+		inet_twsk_free(inet_twsk(sk));
+	else
+		sk_free(sk);
+}
+EXPORT_SYMBOL_GPL(sock_gen_put);
+
 struct sock *__inet_lookup_established(struct net *net,
 				  struct inet_hashinfo *hashinfo,
 				  const __be32 saddr, const __be16 sport,
···
 		if (likely(INET_MATCH(sk, net, acookie,
 				      saddr, daddr, ports, dif))) {
 			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
-				goto begintw;
+				goto out;
 			if (unlikely(!INET_MATCH(sk, net, acookie,
 						 saddr, daddr, ports, dif))) {
-				sock_put(sk);
+				sock_gen_put(sk);
 				goto begin;
 			}
-			goto out;
+			goto found;
 		}
 	}
 	/*
···
 	 */
 	if (get_nulls_value(node) != slot)
 		goto begin;
-
-begintw:
-	/* Must check for a TIME_WAIT'er before going to listener hash. */
-	sk_nulls_for_each_rcu(sk, node, &head->twchain) {
-		if (sk->sk_hash != hash)
-			continue;
-		if (likely(INET_TW_MATCH(sk, net, acookie,
-					 saddr, daddr, ports,
-					 dif))) {
-			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt))) {
-				sk = NULL;
-				goto out;
-			}
-			if (unlikely(!INET_TW_MATCH(sk, net, acookie,
-						    saddr, daddr, ports,
-						    dif))) {
-				inet_twsk_put(inet_twsk(sk));
-				goto begintw;
-			}
-			goto out;
-		}
-	}
-	/*
-	 * if the nulls value we got at the end of this lookup is
-	 * not the expected one, we must restart lookup.
-	 * We probably met an item that was moved to another chain.
-	 */
-	if (get_nulls_value(node) != slot)
-		goto begintw;
-	sk = NULL;
 out:
+	sk = NULL;
+found:
 	rcu_read_unlock();
 	return sk;
 }
···
 	spinlock_t *lock = inet_ehash_lockp(hinfo, hash);
 	struct sock *sk2;
 	const struct hlist_nulls_node *node;
-	struct inet_timewait_sock *tw;
+	struct inet_timewait_sock *tw = NULL;
 	int twrefcnt = 0;
 
 	spin_lock(lock);
 
-	/* Check TIME-WAIT sockets first. */
-	sk_nulls_for_each(sk2, node, &head->twchain) {
-		if (sk2->sk_hash != hash)
-			continue;
-
-		if (likely(INET_TW_MATCH(sk2, net, acookie,
-					 saddr, daddr, ports, dif))) {
-			tw = inet_twsk(sk2);
-			if (twsk_unique(sk, sk2, twp))
-				goto unique;
-			else
-				goto not_unique;
-		}
-	}
-	tw = NULL;
-
-	/* And established part... */
 	sk_nulls_for_each(sk2, node, &head->chain) {
 		if (sk2->sk_hash != hash)
 			continue;
+
 		if (likely(INET_MATCH(sk2, net, acookie,
-				      saddr, daddr, ports, dif)))
+					 saddr, daddr, ports, dif))) {
+			if (sk2->sk_state == TCP_TIME_WAIT) {
+				tw = inet_twsk(sk2);
+				if (twsk_unique(sk, sk2, twp))
+					break;
+			}
 			goto not_unique;
+		}
 	}
 
-unique:
 	/* Must record num and sport now. Otherwise we will see
-	 * in hash table socket with a funny identity. */
+	 * in hash table socket with a funny identity.
+	 */
 	inet->inet_num = lport;
 	inet->inet_sport = htons(lport);
 	sk->sk_hash = hash;

net/ipv4/inet_timewait_sock.c

···
 	refcnt += inet_twsk_bind_unhash(tw, hashinfo);
 	spin_unlock(&bhead->lock);
 
-#ifdef SOCK_REFCNT_DEBUG
-	if (atomic_read(&tw->tw_refcnt) != 1) {
-		pr_debug("%s timewait_sock %p refcnt=%d\n",
-			 tw->tw_prot->name, tw, atomic_read(&tw->tw_refcnt));
-	}
-#endif
-	while (refcnt) {
-		inet_twsk_put(tw);
-		refcnt--;
-	}
+	BUG_ON(refcnt >= atomic_read(&tw->tw_refcnt));
+	atomic_sub(refcnt, &tw->tw_refcnt);
 }
 
-static noinline void inet_twsk_free(struct inet_timewait_sock *tw)
+void inet_twsk_free(struct inet_timewait_sock *tw)
 {
 	struct module *owner = tw->tw_prot->owner;
 	twsk_destructor((struct sock *)tw);
···
 		inet_twsk_free(tw);
 }
 EXPORT_SYMBOL_GPL(inet_twsk_put);
+
+static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
+				   struct hlist_nulls_head *list)
+{
+	hlist_nulls_add_head_rcu(&tw->tw_node, list);
+}
+
+static void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
+				    struct hlist_head *list)
+{
+	hlist_add_head(&tw->tw_bind_node, list);
+}
 
 /*
  * Enter the time wait state. This is called with locally disabled BH.
···
 	spin_lock(lock);
 
 	/*
-	 * Step 2: Hash TW into TIMEWAIT chain.
-	 * Should be done before removing sk from established chain
-	 * because readers are lockless and search established first.
+	 * Step 2: Hash TW into tcp ehash chain.
+	 * Notes :
+	 * - tw_refcnt is set to 3 because :
+	 * - We have one reference from bhash chain.
+	 * - We have one reference from ehash chain.
+	 * We can use atomic_set() because prior spin_lock()/spin_unlock()
+	 * committed into memory all tw fields.
 	 */
-	inet_twsk_add_node_rcu(tw, &ehead->twchain);
+	atomic_set(&tw->tw_refcnt, 1 + 1 + 1);
+	inet_twsk_add_node_rcu(tw, &ehead->chain);
 
-	/* Step 3: Remove SK from established hash. */
+	/* Step 3: Remove SK from hash chain */
 	if (__sk_nulls_del_node_init_rcu(sk))
 		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
-
-	/*
-	 * Notes :
-	 * - We initially set tw_refcnt to 0 in inet_twsk_alloc()
-	 * - We add one reference for the bhash link
-	 * - We add one reference for the ehash link
-	 * - We want this refcnt update done before allowing other
-	 *   threads to find this tw in ehash chain.
-	 */
-	atomic_add(1 + 1 + 1, &tw->tw_refcnt);
 
 	spin_unlock(lock);
 }
···
 restart_rcu:
 		rcu_read_lock();
 restart:
-		sk_nulls_for_each_rcu(sk, node, &head->twchain) {
+		sk_nulls_for_each_rcu(sk, node, &head->chain) {
+			if (sk->sk_state != TCP_TIME_WAIT)
+				continue;
 			tw = inet_twsk(sk);
 			if ((tw->tw_family != family) ||
 				atomic_read(&twsk_net(tw)->count))

net/ipv4/tcp.c

···
 					&tcp_hashinfo.ehash_mask,
 					0,
 					thash_entries ? 0 : 512 * 1024);
-	for (i = 0; i <= tcp_hashinfo.ehash_mask; i++) {
+	for (i = 0; i <= tcp_hashinfo.ehash_mask; i++)
 		INIT_HLIST_NULLS_HEAD(&tcp_hashinfo.ehash[i].chain, i);
-		INIT_HLIST_NULLS_HEAD(&tcp_hashinfo.ehash[i].twchain, i);
-	}
+
 	if (inet_ehash_locks_alloc(&tcp_hashinfo))
 		panic("TCP: failed to alloc ehash_locks");
 	tcp_hashinfo.bhash =

net/ipv4/tcp_ipv4.c

···
 #ifdef CONFIG_PROC_FS
 /* Proc filesystem TCP sock list dumping. */
 
-static inline struct inet_timewait_sock *tw_head(struct hlist_nulls_head *head)
-{
-	return hlist_nulls_empty(head) ? NULL :
-		list_entry(head->first, struct inet_timewait_sock, tw_node);
-}
-
-static inline struct inet_timewait_sock *tw_next(struct inet_timewait_sock *tw)
-{
-	return !is_a_nulls(tw->tw_node.next) ?
-		hlist_nulls_entry(tw->tw_node.next, typeof(*tw), tw_node) : NULL;
-}
-
 /*
  * Get next listener socket follow cur.  If cur is NULL, get first socket
  * starting from bucket given in st->bucket; when st->bucket is zero the
···
 	return rc;
 }
 
-static inline bool empty_bucket(struct tcp_iter_state *st)
+static inline bool empty_bucket(const struct tcp_iter_state *st)
 {
-	return hlist_nulls_empty(&tcp_hashinfo.ehash[st->bucket].chain) &&
-		hlist_nulls_empty(&tcp_hashinfo.ehash[st->bucket].twchain);
+	return hlist_nulls_empty(&tcp_hashinfo.ehash[st->bucket].chain);
 }
 
 /*
···
 	for (; st->bucket <= tcp_hashinfo.ehash_mask; ++st->bucket) {
 		struct sock *sk;
 		struct hlist_nulls_node *node;
-		struct inet_timewait_sock *tw;
 		spinlock_t *lock = inet_ehash_lockp(&tcp_hashinfo, st->bucket);
 
 		/* Lockless fast path for the common case of empty buckets */
···
 			rc = sk;
 			goto out;
 		}
-		st->state = TCP_SEQ_STATE_TIME_WAIT;
-		inet_twsk_for_each(tw, node,
-				   &tcp_hashinfo.ehash[st->bucket].twchain) {
-			if (tw->tw_family != st->family ||
-			    !net_eq(twsk_net(tw), net)) {
-				continue;
-			}
-			rc = tw;
-			goto out;
-		}
 		spin_unlock_bh(lock);
-		st->state = TCP_SEQ_STATE_ESTABLISHED;
 	}
 out:
 	return rc;
···
 static void *established_get_next(struct seq_file *seq, void *cur)
 {
 	struct sock *sk = cur;
-	struct inet_timewait_sock *tw;
 	struct hlist_nulls_node *node;
 	struct tcp_iter_state *st = seq->private;
 	struct net *net = seq_file_net(seq);
···
 	++st->num;
 	++st->offset;
 
-	if (st->state == TCP_SEQ_STATE_TIME_WAIT) {
-		tw = cur;
-		tw = tw_next(tw);
-get_tw:
-		while (tw && (tw->tw_family != st->family || !net_eq(twsk_net(tw), net))) {
-			tw = tw_next(tw);
-		}
-		if (tw) {
-			cur = tw;
-			goto out;
-		}
-		spin_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
-		st->state = TCP_SEQ_STATE_ESTABLISHED;
-
-		/* Look for next non empty bucket */
-		st->offset = 0;
-		while (++st->bucket <= tcp_hashinfo.ehash_mask &&
-				empty_bucket(st))
-			;
-		if (st->bucket > tcp_hashinfo.ehash_mask)
-			return NULL;
-
-		spin_lock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
-		sk = sk_nulls_head(&tcp_hashinfo.ehash[st->bucket].chain);
-	} else
-		sk = sk_nulls_next(sk);
+	sk = sk_nulls_next(sk);
 
 	sk_nulls_for_each_from(sk, node) {
 		if (sk->sk_family == st->family && net_eq(sock_net(sk), net))
-			goto found;
+			return sk;
 	}
 
-	st->state = TCP_SEQ_STATE_TIME_WAIT;
-	tw = tw_head(&tcp_hashinfo.ehash[st->bucket].twchain);
-	goto get_tw;
-found:
-	cur = sk;
-out:
-	return cur;
+	spin_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
+	++st->bucket;
+	return established_get_first(seq);
 }
 
 static void *established_get_idx(struct seq_file *seq, loff_t pos)
···
 		if (rc)
 			break;
 		st->bucket = 0;
+		st->state = TCP_SEQ_STATE_ESTABLISHED;
 		/* Fallthrough */
 	case TCP_SEQ_STATE_ESTABLISHED:
-	case TCP_SEQ_STATE_TIME_WAIT:
-		st->state = TCP_SEQ_STATE_ESTABLISHED;
 		if (st->bucket > tcp_hashinfo.ehash_mask)
 			break;
 		rc = established_get_first(seq);
···
 		}
 		break;
 	case TCP_SEQ_STATE_ESTABLISHED:
-	case TCP_SEQ_STATE_TIME_WAIT:
 		rc = established_get_next(seq, v);
 		break;
 	}
···
 		if (v != SEQ_START_TOKEN)
 			spin_unlock_bh(&tcp_hashinfo.listening_hash[st->bucket].lock);
 		break;
-	case TCP_SEQ_STATE_TIME_WAIT:
 	case TCP_SEQ_STATE_ESTABLISHED:
 		if (v)
 			spin_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
···
 static int tcp4_seq_show(struct seq_file *seq, void *v)
 {
 	struct tcp_iter_state *st;
+	struct sock *sk = v;
 	int len;
 
 	if (v == SEQ_START_TOKEN) {
···
 	switch (st->state) {
 	case TCP_SEQ_STATE_LISTENING:
 	case TCP_SEQ_STATE_ESTABLISHED:
-		get_tcp4_sock(v, seq, st->num, &len);
+		if (sk->sk_state == TCP_TIME_WAIT)
+			get_timewait4_sock(v, seq, st->num, &len);
+		else
+			get_tcp4_sock(v, seq, st->num, &len);
 		break;
 	case TCP_SEQ_STATE_OPENREQ:
 		get_openreq4(st->syn_wait_sk, v, seq, st->num, st->uid, &len);
-		break;
-	case TCP_SEQ_STATE_TIME_WAIT:
-		get_timewait4_sock(v, seq, st->num, &len);
 		break;
 	}
 	seq_printf(seq, "%*s\n", TMPSZ - 1 - len, "");

net/ipv6/inet6_hashtables.c

···
 	sk_nulls_for_each_rcu(sk, node, &head->chain) {
 		if (sk->sk_hash != hash)
 			continue;
-		if (likely(INET6_MATCH(sk, net, saddr, daddr, ports, dif))) {
-			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
-				goto begintw;
+		if (sk->sk_state == TCP_TIME_WAIT) {
+			if (!INET6_TW_MATCH(sk, net, saddr, daddr, ports, dif))
+				continue;
+		} else {
+			if (!INET6_MATCH(sk, net, saddr, daddr, ports, dif))
+				continue;
+		}
+		if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
+			goto out;
+
+		if (sk->sk_state == TCP_TIME_WAIT) {
+			if (unlikely(!INET6_TW_MATCH(sk, net, saddr, daddr,
+						     ports, dif))) {
+				sock_gen_put(sk);
+				goto begin;
+			}
+		} else {
 			if (unlikely(!INET6_MATCH(sk, net, saddr, daddr,
 						  ports, dif))) {
 				sock_put(sk);
 				goto begin;
 			}
-		goto out;
+		goto found;
 		}
 	}
 	if (get_nulls_value(node) != slot)
 		goto begin;
-
-begintw:
-	/* Must check for a TIME_WAIT'er before going to listener hash. */
-	sk_nulls_for_each_rcu(sk, node, &head->twchain) {
-		if (sk->sk_hash != hash)
-			continue;
-		if (likely(INET6_TW_MATCH(sk, net, saddr, daddr,
-					  ports, dif))) {
-			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt))) {
-				sk = NULL;
-				goto out;
-			}
-			if (unlikely(!INET6_TW_MATCH(sk, net, saddr, daddr,
-						     ports, dif))) {
-				inet_twsk_put(inet_twsk(sk));
-				goto begintw;
-			}
-			goto out;
-		}
-	}
-	if (get_nulls_value(node) != slot)
-		goto begintw;
-	sk = NULL;
 out:
+	sk = NULL;
+found:
 	rcu_read_unlock();
 	return sk;
 }
···
 	spinlock_t *lock = inet_ehash_lockp(hinfo, hash);
 	struct sock *sk2;
 	const struct hlist_nulls_node *node;
-	struct inet_timewait_sock *tw;
+	struct inet_timewait_sock *tw = NULL;
 	int twrefcnt = 0;
 
 	spin_lock(lock);
 
-	/* Check TIME-WAIT sockets first. */
-	sk_nulls_for_each(sk2, node, &head->twchain) {
-		if (sk2->sk_hash != hash)
-			continue;
-
-		if (likely(INET6_TW_MATCH(sk2, net, saddr, daddr,
-					  ports, dif))) {
-			tw = inet_twsk(sk2);
-			if (twsk_unique(sk, sk2, twp))
-				goto unique;
-			else
-				goto not_unique;
-		}
-	}
-	tw = NULL;
-
-	/* And established part... */
 	sk_nulls_for_each(sk2, node, &head->chain) {
 		if (sk2->sk_hash != hash)
 			continue;
+
+		if (sk2->sk_state == TCP_TIME_WAIT) {
+			if (likely(INET6_TW_MATCH(sk2, net, saddr, daddr,
+						  ports, dif))) {
+				tw = inet_twsk(sk2);
+				if (twsk_unique(sk, sk2, twp))
+					goto unique;
+				else
+					goto not_unique;
+			}
+		}
 		if (likely(INET6_MATCH(sk2, net, saddr, daddr, ports, dif)))
 			goto not_unique;
 	}

net/ipv6/tcp_ipv6.c

···
 static int tcp6_seq_show(struct seq_file *seq, void *v)
 {
 	struct tcp_iter_state *st;
+	struct sock *sk = v;
 
 	if (v == SEQ_START_TOKEN) {
 		seq_puts(seq,
···
 	switch (st->state) {
 	case TCP_SEQ_STATE_LISTENING:
 	case TCP_SEQ_STATE_ESTABLISHED:
-		get_tcp6_sock(seq, v, st->num);
+		if (sk->sk_state == TCP_TIME_WAIT)
+			get_timewait6_sock(seq, v, st->num);
+		else
+			get_tcp6_sock(seq, v, st->num);
 		break;
 	case TCP_SEQ_STATE_OPENREQ:
 		get_openreq6(seq, st->syn_wait_sk, v, st->num, st->uid);
-		break;
-	case TCP_SEQ_STATE_TIME_WAIT:
-		get_timewait6_sock(seq, v, st->num);
 		break;
 	}
 out: