net/ipv4/inet_timewait_sock.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * INET		An implementation of the TCP/IP protocol suite for the LINUX
  *		operating system.  INET is implemented using the  BSD Socket
  *		interface as the means of communication with the user level.
  *
  *		Generic TIME_WAIT sockets functions
  *
  *		From code orinally in TCP
  */

 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <net/inet_hashtables.h>
 #include <net/inet_timewait_sock.h>
 #include <net/ip.h>


 /**
  *	inet_twsk_bind_unhash - unhash a timewait socket from bind hash
  *	@tw: timewait socket
  *	@hashinfo: hashinfo pointer
  *
  *	unhash a timewait socket from bind hash, if hashed.
  *	bind hash lock must be held by caller.
  *	Returns 1 if caller should call inet_twsk_put() after lock release.
  */
 void inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
 			  struct inet_hashinfo *hashinfo)
 {
 	struct inet_bind2_bucket *tb2 = tw->tw_tb2;
 	struct inet_bind_bucket *tb = tw->tw_tb;

 	if (!tb)
 		return;

 	__hlist_del(&tw->tw_bind_node);
 	tw->tw_tb = NULL;
 	inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);

 	__hlist_del(&tw->tw_bind2_node);
 	tw->tw_tb2 = NULL;
 	inet_bind2_bucket_destroy(hashinfo->bind2_bucket_cachep, tb2);

 	__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;
 	spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
 	struct inet_bind_hashbucket *bhead, *bhead2;

 	spin_lock(lock);
 	sk_nulls_del_node_init_rcu((struct sock *)tw);
 	spin_unlock(lock);

 	/* Disassociate with bind bucket. */
 	bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
 			hashinfo->bhash_size)];
 	bhead2 = inet_bhashfn_portaddr(hashinfo, (struct sock *)tw,
 				       twsk_net(tw), tw->tw_num);

 	spin_lock(&bhead->lock);
 	spin_lock(&bhead2->lock);
 	inet_twsk_bind_unhash(tw, hashinfo);
 	spin_unlock(&bhead2->lock);
 	spin_unlock(&bhead->lock);

 	refcount_dec(&tw->tw_dr->tw_refcount);
 	inet_twsk_put(tw);
 }

 void inet_twsk_free(struct inet_timewait_sock *tw)
 {
 	struct module *owner = tw->tw_prot->owner;
 	twsk_destructor((struct sock *)tw);
 #ifdef SOCK_REFCNT_DEBUG
 	pr_debug("%s timewait_sock %p released\n", tw->tw_prot->name, tw);
 #endif
 	kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
 	module_put(owner);
 }

 void inet_twsk_put(struct inet_timewait_sock *tw)
 {
 	if (refcount_dec_and_test(&tw->tw_refcnt))
 		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);
 }

 static void inet_twsk_add_bind2_node(struct inet_timewait_sock *tw,
 				     struct hlist_head *list)
 {
 	hlist_add_head(&tw->tw_bind2_node, list);
 }

 /*
  * Enter the time wait state. This is called with locally disabled BH.
  * Essentially we whip up a timewait bucket, copy the relevant info into it
  * from the SK, and mess with hash chains and list linkage.
  */
 void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
 			   struct inet_hashinfo *hashinfo)
 {
 	const struct inet_sock *inet = inet_sk(sk);
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 	struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
 	spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 	struct inet_bind_hashbucket *bhead, *bhead2;

 	/* Step 1: Put TW into bind hash. Original socket stays there too.
 	   Note, that any socket with inet->num != 0 MUST be bound in
 	   binding cache, even if it is closed.
 	 */
 	bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
 			hashinfo->bhash_size)];
 	bhead2 = inet_bhashfn_portaddr(hashinfo, sk, twsk_net(tw), inet->inet_num);

 	spin_lock(&bhead->lock);
 	spin_lock(&bhead2->lock);

 	tw->tw_tb = icsk->icsk_bind_hash;
 	WARN_ON(!icsk->icsk_bind_hash);
 	inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);

 	tw->tw_tb2 = icsk->icsk_bind2_hash;
 	WARN_ON(!icsk->icsk_bind2_hash);
 	inet_twsk_add_bind2_node(tw, &tw->tw_tb2->deathrow);

 	spin_unlock(&bhead2->lock);
 	spin_unlock(&bhead->lock);

 	spin_lock(lock);

 	inet_twsk_add_node_rcu(tw, &ehead->chain);

 	/* 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);

 	spin_unlock(lock);

 	/* tw_refcnt is set to 3 because we have :
 	 * - one reference for bhash chain.
 	 * - one reference for ehash chain.
 	 * - one reference for timer.
 	 * We can use atomic_set() because prior spin_lock()/spin_unlock()
 	 * committed into memory all tw fields.
 	 * Also note that after this point, we lost our implicit reference
 	 * so we are not allowed to use tw anymore.
 	 */
 	refcount_set(&tw->tw_refcnt, 3);
 }
 EXPORT_SYMBOL_GPL(inet_twsk_hashdance);

 static void tw_timer_handler(struct timer_list *t)
 {
 	struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);

 	inet_twsk_kill(tw);
 }

 struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
 					   struct inet_timewait_death_row *dr,
 					   const int state)
 {
 	struct inet_timewait_sock *tw;

 	if (refcount_read(&dr->tw_refcount) - 1 >=
 	    READ_ONCE(dr->sysctl_max_tw_buckets))
 		return NULL;

 	tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
 			      GFP_ATOMIC);
 	if (tw) {
 		const struct inet_sock *inet = inet_sk(sk);

 		tw->tw_dr	    = dr;
 		/* Give us an identity. */
 		tw->tw_daddr	    = inet->inet_daddr;
 		tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
 		tw->tw_bound_dev_if = sk->sk_bound_dev_if;
 		tw->tw_tos	    = inet->tos;
 		tw->tw_num	    = inet->inet_num;
 		tw->tw_state	    = TCP_TIME_WAIT;
 		tw->tw_substate	    = state;
 		tw->tw_sport	    = inet->inet_sport;
 		tw->tw_dport	    = inet->inet_dport;
 		tw->tw_family	    = sk->sk_family;
 		tw->tw_reuse	    = sk->sk_reuse;
 		tw->tw_reuseport    = sk->sk_reuseport;
 		tw->tw_hash	    = sk->sk_hash;
 		tw->tw_ipv6only	    = 0;
 		tw->tw_transparent  = inet->transparent;
 		tw->tw_prot	    = sk->sk_prot_creator;
 		atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
 		twsk_net_set(tw, sock_net(sk));
 		timer_setup(&tw->tw_timer, tw_timer_handler, TIMER_PINNED);
 		/*
 		 * Because we use RCU lookups, we should not set tw_refcnt
 		 * to a non null value before everything is setup for this
 		 * timewait socket.
 		 */
 		refcount_set(&tw->tw_refcnt, 0);

 		__module_get(tw->tw_prot->owner);
 	}

 	return tw;
 }
 EXPORT_SYMBOL_GPL(inet_twsk_alloc);

 /* These are always called from BH context.  See callers in
  * tcp_input.c to verify this.
  */

 /* This is for handling early-kills of TIME_WAIT sockets.
  * Warning : consume reference.
  * Caller should not access tw anymore.
  */
 void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
 {
 	if (del_timer_sync(&tw->tw_timer))
 		inet_twsk_kill(tw);
 	inet_twsk_put(tw);
 }
 EXPORT_SYMBOL(inet_twsk_deschedule_put);

 void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
 {
 	/* timeout := RTO * 3.5
 	 *
 	 * 3.5 = 1+2+0.5 to wait for two retransmits.
 	 *
 	 * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
 	 * our ACK acking that FIN can be lost. If N subsequent retransmitted
 	 * FINs (or previous seqments) are lost (probability of such event
 	 * is p^(N+1), where p is probability to lose single packet and
 	 * time to detect the loss is about RTO*(2^N - 1) with exponential
 	 * backoff). Normal timewait length is calculated so, that we
 	 * waited at least for one retransmitted FIN (maximal RTO is 120sec).
 	 * [ BTW Linux. following BSD, violates this requirement waiting
 	 *   only for 60sec, we should wait at least for 240 secs.
 	 *   Well, 240 consumes too much of resources 8)
 	 * ]
 	 * This interval is not reduced to catch old duplicate and
 	 * responces to our wandering segments living for two MSLs.
 	 * However, if we use PAWS to detect
 	 * old duplicates, we can reduce the interval to bounds required
 	 * by RTO, rather than MSL. So, if peer understands PAWS, we
 	 * kill tw bucket after 3.5*RTO (it is important that this number
 	 * is greater than TS tick!) and detect old duplicates with help
 	 * of PAWS.
 	 */

 	if (!rearm) {
 		bool kill = timeo <= 4*HZ;

 		__NET_INC_STATS(twsk_net(tw), kill ? LINUX_MIB_TIMEWAITKILLED :
 						     LINUX_MIB_TIMEWAITED);
 		BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
 		refcount_inc(&tw->tw_dr->tw_refcount);
 	} else {
 		mod_timer_pending(&tw->tw_timer, jiffies + timeo);
 	}
 }
 EXPORT_SYMBOL_GPL(__inet_twsk_schedule);

 /* Remove all non full sockets (TIME_WAIT and NEW_SYN_RECV) for dead netns */
 void inet_twsk_purge(struct inet_hashinfo *hashinfo)
 {
 	struct inet_ehash_bucket *head = &hashinfo->ehash[0];
 	unsigned int ehash_mask = hashinfo->ehash_mask;
 	struct hlist_nulls_node *node;
 	unsigned int slot;
 	struct sock *sk;

 	for (slot = 0; slot <= ehash_mask; slot++, head++) {
 		if (hlist_nulls_empty(&head->chain))
 			continue;

 restart_rcu:
 		cond_resched();
 		rcu_read_lock();
 restart:
 		sk_nulls_for_each_rcu(sk, node, &head->chain) {
 			int state = inet_sk_state_load(sk);

 			if ((1 << state) & ~(TCPF_TIME_WAIT |
 					     TCPF_NEW_SYN_RECV))
 				continue;

 			if (refcount_read(&sock_net(sk)->ns.count))
 				continue;

 			if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
 				continue;

 			if (refcount_read(&sock_net(sk)->ns.count)) {
 				sock_gen_put(sk);
 				goto restart;
 			}

 			rcu_read_unlock();
 			local_bh_disable();
 			if (state == TCP_TIME_WAIT) {
 				inet_twsk_deschedule_put(inet_twsk(sk));
 			} else {
 				struct request_sock *req = inet_reqsk(sk);

 				inet_csk_reqsk_queue_drop_and_put(req->rsk_listener,
 								  req);
 			}
 			local_bh_enable();
 			goto restart_rcu;
 		}
 		/* 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 restart;
 		rcu_read_unlock();
 	}
 }
 EXPORT_SYMBOL_GPL(inet_twsk_purge);
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* INET An implementation of the TCP/IP protocol suite for the LINUX
	* operating system. INET is implemented using the BSD Socket
	* interface as the means of communication with the user level.
	*
	* Generic TIME_WAIT sockets functions
	*
	* From code orinally in TCP
	*/

	#include <linux/kernel.h>
	#include <linux/slab.h>
	#include <linux/module.h>
	#include <net/inet_hashtables.h>
	#include <net/inet_timewait_sock.h>
	#include <net/ip.h>


	/**
	* inet_twsk_bind_unhash - unhash a timewait socket from bind hash
	* @tw: timewait socket
	* @hashinfo: hashinfo pointer
	*
	* unhash a timewait socket from bind hash, if hashed.
	* bind hash lock must be held by caller.
	* Returns 1 if caller should call inet_twsk_put() after lock release.
	*/
	void inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
	struct inet_hashinfo *hashinfo)
	{
	struct inet_bind2_bucket *tb2 = tw->tw_tb2;
	struct inet_bind_bucket *tb = tw->tw_tb;

	if (!tb)
	return;

	__hlist_del(&tw->tw_bind_node);
	tw->tw_tb = NULL;
	inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);

	__hlist_del(&tw->tw_bind2_node);
	tw->tw_tb2 = NULL;
	inet_bind2_bucket_destroy(hashinfo->bind2_bucket_cachep, tb2);

	__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;
	spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
	struct inet_bind_hashbucket bhead, bhead2;

	spin_lock(lock);
	sk_nulls_del_node_init_rcu((struct sock *)tw);
	spin_unlock(lock);

	/* Disassociate with bind bucket. */
	bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
	hashinfo->bhash_size)];
	bhead2 = inet_bhashfn_portaddr(hashinfo, (struct sock *)tw,
	twsk_net(tw), tw->tw_num);

	spin_lock(&bhead->lock);
	spin_lock(&bhead2->lock);
	inet_twsk_bind_unhash(tw, hashinfo);
	spin_unlock(&bhead2->lock);
	spin_unlock(&bhead->lock);

	refcount_dec(&tw->tw_dr->tw_refcount);
	inet_twsk_put(tw);
	}

	void inet_twsk_free(struct inet_timewait_sock *tw)
	{
	struct module *owner = tw->tw_prot->owner;
	twsk_destructor((struct sock *)tw);
	#ifdef SOCK_REFCNT_DEBUG
	pr_debug("%s timewait_sock %p released\n", tw->tw_prot->name, tw);
	#endif
	kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
	module_put(owner);
	}

	void inet_twsk_put(struct inet_timewait_sock *tw)
	{
	if (refcount_dec_and_test(&tw->tw_refcnt))
	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);
	}

	static void inet_twsk_add_bind2_node(struct inet_timewait_sock *tw,
	struct hlist_head *list)
	{
	hlist_add_head(&tw->tw_bind2_node, list);
	}

	/*
	* Enter the time wait state. This is called with locally disabled BH.
	* Essentially we whip up a timewait bucket, copy the relevant info into it
	* from the SK, and mess with hash chains and list linkage.
	*/
	void inet_twsk_hashdance(struct inet_timewait_sock tw, struct sock sk,
	struct inet_hashinfo *hashinfo)
	{
	const struct inet_sock *inet = inet_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
	spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
	struct inet_bind_hashbucket bhead, bhead2;

	/* Step 1: Put TW into bind hash. Original socket stays there too.
	Note, that any socket with inet->num != 0 MUST be bound in
	binding cache, even if it is closed.
	*/
	bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
	hashinfo->bhash_size)];
	bhead2 = inet_bhashfn_portaddr(hashinfo, sk, twsk_net(tw), inet->inet_num);

	spin_lock(&bhead->lock);
	spin_lock(&bhead2->lock);

	tw->tw_tb = icsk->icsk_bind_hash;
	WARN_ON(!icsk->icsk_bind_hash);
	inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);

	tw->tw_tb2 = icsk->icsk_bind2_hash;
	WARN_ON(!icsk->icsk_bind2_hash);
	inet_twsk_add_bind2_node(tw, &tw->tw_tb2->deathrow);

	spin_unlock(&bhead2->lock);
	spin_unlock(&bhead->lock);

	spin_lock(lock);

	inet_twsk_add_node_rcu(tw, &ehead->chain);

	/* 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);

	spin_unlock(lock);

	/* tw_refcnt is set to 3 because we have :
	* - one reference for bhash chain.
	* - one reference for ehash chain.
	* - one reference for timer.
	* We can use atomic_set() because prior spin_lock()/spin_unlock()
	* committed into memory all tw fields.
	* Also note that after this point, we lost our implicit reference
	* so we are not allowed to use tw anymore.
	*/
	refcount_set(&tw->tw_refcnt, 3);
	}
	EXPORT_SYMBOL_GPL(inet_twsk_hashdance);

	static void tw_timer_handler(struct timer_list *t)
	{
	struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);

	inet_twsk_kill(tw);
	}

	struct inet_timewait_sock inet_twsk_alloc(const struct sock sk,
	struct inet_timewait_death_row *dr,
	const int state)
	{
	struct inet_timewait_sock *tw;

	if (refcount_read(&dr->tw_refcount) - 1 >=
	READ_ONCE(dr->sysctl_max_tw_buckets))
	return NULL;

	tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
	GFP_ATOMIC);
	if (tw) {
	const struct inet_sock *inet = inet_sk(sk);

	tw->tw_dr = dr;
	/* Give us an identity. */
	tw->tw_daddr = inet->inet_daddr;
	tw->tw_rcv_saddr = inet->inet_rcv_saddr;
	tw->tw_bound_dev_if = sk->sk_bound_dev_if;
	tw->tw_tos = inet->tos;
	tw->tw_num = inet->inet_num;
	tw->tw_state = TCP_TIME_WAIT;
	tw->tw_substate = state;
	tw->tw_sport = inet->inet_sport;
	tw->tw_dport = inet->inet_dport;
	tw->tw_family = sk->sk_family;
	tw->tw_reuse = sk->sk_reuse;
	tw->tw_reuseport = sk->sk_reuseport;
	tw->tw_hash = sk->sk_hash;
	tw->tw_ipv6only = 0;
	tw->tw_transparent = inet->transparent;
	tw->tw_prot = sk->sk_prot_creator;
	atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
	twsk_net_set(tw, sock_net(sk));
	timer_setup(&tw->tw_timer, tw_timer_handler, TIMER_PINNED);
	/*
	* Because we use RCU lookups, we should not set tw_refcnt
	* to a non null value before everything is setup for this
	* timewait socket.
	*/
	refcount_set(&tw->tw_refcnt, 0);

	__module_get(tw->tw_prot->owner);
	}

	return tw;
	}
	EXPORT_SYMBOL_GPL(inet_twsk_alloc);

	/* These are always called from BH context. See callers in
	* tcp_input.c to verify this.
	*/

	/* This is for handling early-kills of TIME_WAIT sockets.
	* Warning : consume reference.
	* Caller should not access tw anymore.
	*/
	void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
	{
	if (del_timer_sync(&tw->tw_timer))
	inet_twsk_kill(tw);
	inet_twsk_put(tw);
	}
	EXPORT_SYMBOL(inet_twsk_deschedule_put);

	void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
	{
	/* timeout := RTO * 3.5
	*
	* 3.5 = 1+2+0.5 to wait for two retransmits.
	*
	* RATIONALE: if FIN arrived and we entered TIME-WAIT state,
	* our ACK acking that FIN can be lost. If N subsequent retransmitted
	* FINs (or previous seqments) are lost (probability of such event
	* is p^(N+1), where p is probability to lose single packet and
	* time to detect the loss is about RTO*(2^N - 1) with exponential
	* backoff). Normal timewait length is calculated so, that we
	* waited at least for one retransmitted FIN (maximal RTO is 120sec).
	* [ BTW Linux. following BSD, violates this requirement waiting
	* only for 60sec, we should wait at least for 240 secs.
	* Well, 240 consumes too much of resources 8)
	* ]
	* This interval is not reduced to catch old duplicate and
	* responces to our wandering segments living for two MSLs.
	* However, if we use PAWS to detect
	* old duplicates, we can reduce the interval to bounds required
	* by RTO, rather than MSL. So, if peer understands PAWS, we
	* kill tw bucket after 3.5*RTO (it is important that this number
	* is greater than TS tick!) and detect old duplicates with help
	* of PAWS.
	*/

	if (!rearm) {
	bool kill = timeo <= 4*HZ;

	__NET_INC_STATS(twsk_net(tw), kill ? LINUX_MIB_TIMEWAITKILLED :
	LINUX_MIB_TIMEWAITED);
	BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
	refcount_inc(&tw->tw_dr->tw_refcount);
	} else {
	mod_timer_pending(&tw->tw_timer, jiffies + timeo);
	}
	}
	EXPORT_SYMBOL_GPL(__inet_twsk_schedule);

	/* Remove all non full sockets (TIME_WAIT and NEW_SYN_RECV) for dead netns */
	void inet_twsk_purge(struct inet_hashinfo *hashinfo)
	{
	struct inet_ehash_bucket *head = &hashinfo->ehash[0];
	unsigned int ehash_mask = hashinfo->ehash_mask;
	struct hlist_nulls_node *node;
	unsigned int slot;
	struct sock *sk;

	for (slot = 0; slot <= ehash_mask; slot++, head++) {
	if (hlist_nulls_empty(&head->chain))
	continue;

	restart_rcu:
	cond_resched();
	rcu_read_lock();
	restart:
	sk_nulls_for_each_rcu(sk, node, &head->chain) {
	int state = inet_sk_state_load(sk);

	if ((1 << state) & ~(TCPF_TIME_WAIT \|
	TCPF_NEW_SYN_RECV))
	continue;

	if (refcount_read(&sock_net(sk)->ns.count))
	continue;

	if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
	continue;

	if (refcount_read(&sock_net(sk)->ns.count)) {
	sock_gen_put(sk);
	goto restart;
	}

	rcu_read_unlock();
	local_bh_disable();
	if (state == TCP_TIME_WAIT) {
	inet_twsk_deschedule_put(inet_twsk(sk));
	} else {
	struct request_sock *req = inet_reqsk(sk);

	inet_csk_reqsk_queue_drop_and_put(req->rsk_listener,
	req);
	}
	local_bh_enable();
	goto restart_rcu;
	}
	/* 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 restart;
	rcu_read_unlock();
	}
	}
	EXPORT_SYMBOL_GPL(inet_twsk_purge);