inet: simplify timewait refcounting

timewait sockets have a complex refcounting logic.
Once we realize it should be similar to established and
syn_recv sockets, we can use sk_nulls_del_node_init_rcu()
and remove inet_twsk_unhash()

In particular, deferred inet_twsk_put() added in commit
13475a30b66cd ("tcp: connect() race with timewait reuse")
looks unecessary : When removing a timewait socket from
ehash or bhash, caller must own a reference on the socket
anyway.

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

include/net/inet_hashtables.h

···
 
 void inet_hashinfo_init(struct inet_hashinfo *h);
 
-int __inet_hash_nolisten(struct sock *sk, struct inet_timewait_sock *tw);
-int __inet_hash(struct sock *sk, struct inet_timewait_sock *tw);
+void __inet_hash_nolisten(struct sock *sk, struct sock *osk);
+void __inet_hash(struct sock *sk, struct sock *osk);
 void inet_hash(struct sock *sk);
 void inet_unhash(struct sock *sk);
 

include/net/inet_timewait_sock.h

···
 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);
-
-int inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
-			  struct inet_hashinfo *hashinfo);
+void inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
+			   struct inet_hashinfo *hashinfo);
 
 struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
 					   struct inet_timewait_death_row *dr,

net/ipv4/inet_hashtables.c

···
 	struct sock *sk2;
 	const struct hlist_nulls_node *node;
 	struct inet_timewait_sock *tw = NULL;
-	int twrefcnt = 0;
 
 	spin_lock(lock);
 
···
 	WARN_ON(!sk_unhashed(sk));
 	__sk_nulls_add_node_rcu(sk, &head->chain);
 	if (tw) {
-		twrefcnt = inet_twsk_unhash(tw);
+		sk_nulls_del_node_init_rcu((struct sock *)tw);
 		NET_INC_STATS_BH(net, LINUX_MIB_TIMEWAITRECYCLED);
 	}
 	spin_unlock(lock);
-	if (twrefcnt)
-		inet_twsk_put(tw);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 
 	if (twp) {
···
 	} else if (tw) {
 		/* Silly. Should hash-dance instead... */
 		inet_twsk_deschedule(tw);
-
 		inet_twsk_put(tw);
 	}
 	return 0;
···
 					  inet->inet_dport);
 }
 
-int __inet_hash_nolisten(struct sock *sk, struct inet_timewait_sock *tw)
+void __inet_hash_nolisten(struct sock *sk, struct sock *osk)
 {
 	struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
 	struct hlist_nulls_head *list;
 	struct inet_ehash_bucket *head;
 	spinlock_t *lock;
-	int twrefcnt = 0;
 
 	WARN_ON(!sk_unhashed(sk));
 
···
 
 	spin_lock(lock);
 	__sk_nulls_add_node_rcu(sk, list);
-	if (tw) {
-		WARN_ON(sk->sk_hash != tw->tw_hash);
-		twrefcnt = inet_twsk_unhash(tw);
+	if (osk) {
+		WARN_ON(sk->sk_hash != osk->sk_hash);
+		sk_nulls_del_node_init_rcu(osk);
 	}
 	spin_unlock(lock);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
-	return twrefcnt;
 }
 EXPORT_SYMBOL_GPL(__inet_hash_nolisten);
 
-int __inet_hash(struct sock *sk, struct inet_timewait_sock *tw)
+void __inet_hash(struct sock *sk, struct sock *osk)
 {
 	struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
 	struct inet_listen_hashbucket *ilb;
 
 	if (sk->sk_state != TCP_LISTEN)
-		return __inet_hash_nolisten(sk, tw);
+		return __inet_hash_nolisten(sk, osk);
 
 	WARN_ON(!sk_unhashed(sk));
 	ilb = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
···
 	__sk_nulls_add_node_rcu(sk, &ilb->head);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 	spin_unlock(&ilb->lock);
-	return 0;
 }
 EXPORT_SYMBOL(__inet_hash);
 
···
 	struct inet_bind_bucket *tb;
 	int ret;
 	struct net *net = sock_net(sk);
-	int twrefcnt = 1;
 
 	if (!snum) {
 		int i, remaining, low, high, port;
···
 		inet_bind_hash(sk, tb, port);
 		if (sk_unhashed(sk)) {
 			inet_sk(sk)->inet_sport = htons(port);
-			twrefcnt += __inet_hash_nolisten(sk, tw);
+			__inet_hash_nolisten(sk, (struct sock *)tw);
 		}
 		if (tw)
-			twrefcnt += inet_twsk_bind_unhash(tw, hinfo);
+			inet_twsk_bind_unhash(tw, hinfo);
 		spin_unlock(&head->lock);
 
 		if (tw) {
 			inet_twsk_deschedule(tw);
-			while (twrefcnt) {
-				twrefcnt--;
-				inet_twsk_put(tw);
-			}
+			inet_twsk_put(tw);
 		}
 
 		ret = 0;

net/ipv4/inet_timewait_sock.c

···
 
 
 /**
- *	inet_twsk_unhash - unhash a timewait socket from established hash
- *	@tw: timewait socket
- *
- *	unhash a timewait socket from established hash, if hashed.
- *	ehash lock must be held by caller.
- *	Returns 1 if caller should call inet_twsk_put() after lock release.
- */
-int inet_twsk_unhash(struct inet_timewait_sock *tw)
-{
-	if (hlist_nulls_unhashed(&tw->tw_node))
-		return 0;
-
-	hlist_nulls_del_rcu(&tw->tw_node);
-	sk_nulls_node_init(&tw->tw_node);
-	/*
-	 * We cannot call inet_twsk_put() ourself under lock,
-	 * caller must call it for us.
-	 */
-	return 1;
-}
-
-/**
  *	inet_twsk_bind_unhash - unhash a timewait socket from bind hash
  *	@tw: timewait socket
  *	@hashinfo: hashinfo pointer
···
  *	bind hash lock must be held by caller.
  *	Returns 1 if caller should call inet_twsk_put() after lock release.
  */
-int inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
+void inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
 			  struct inet_hashinfo *hashinfo)
 {
 	struct inet_bind_bucket *tb = tw->tw_tb;
 
 	if (!tb)
-		return 0;
+		return;
 
 	__hlist_del(&tw->tw_bind_node);
 	tw->tw_tb = NULL;
 	inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
-	/*
-	 * We cannot call inet_twsk_put() ourself under lock,
-	 * caller must call it for us.
-	 */
-	return 1;
+	__sock_put((struct sock *)tw);
 }
 
 /* Must be called with locally disabled BHs. */
 static void inet_twsk_kill(struct inet_timewait_sock *tw)
 {
 	struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
-	struct inet_bind_hashbucket *bhead;
-	int refcnt;
-	/* Unlink from established hashes. */
 	spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
+	struct inet_bind_hashbucket *bhead;
 
 	spin_lock(lock);
-	refcnt = inet_twsk_unhash(tw);
+	sk_nulls_del_node_init_rcu((struct sock *)tw);
 	spin_unlock(lock);
 
 	/* Disassociate with bind bucket. */
···
 			hashinfo->bhash_size)];
 
 	spin_lock(&bhead->lock);
-	refcnt += inet_twsk_bind_unhash(tw, hashinfo);
+	inet_twsk_bind_unhash(tw, hashinfo);
 	spin_unlock(&bhead->lock);
 
-	BUG_ON(refcnt >= atomic_read(&tw->tw_refcnt));
-	atomic_sub(refcnt, &tw->tw_refcnt);
 	atomic_dec(&tw->tw_dr->tw_count);
 	inet_twsk_put(tw);
 }

net/ipv6/inet6_hashtables.c

···
 	struct sock *sk2;
 	const struct hlist_nulls_node *node;
 	struct inet_timewait_sock *tw = NULL;
-	int twrefcnt = 0;
 
 	spin_lock(lock);
 
···
 	WARN_ON(!sk_unhashed(sk));
 	__sk_nulls_add_node_rcu(sk, &head->chain);
 	if (tw) {
-		twrefcnt = inet_twsk_unhash(tw);
+		sk_nulls_del_node_init_rcu((struct sock *)tw);
 		NET_INC_STATS_BH(net, LINUX_MIB_TIMEWAITRECYCLED);
 	}
 	spin_unlock(lock);
-	if (twrefcnt)
-		inet_twsk_put(tw);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 
 	if (twp) {
···
 	} else if (tw) {
 		/* Silly. Should hash-dance instead... */
 		inet_twsk_deschedule(tw);
-
 		inet_twsk_put(tw);
 	}
 	return 0;