net/ipv4/inet_timewait_sock.c - fp2-dev/kernel/msm - Gitiles

 /*
  * 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 <net/inet_hashtables.h>
 #include <net/inet_timewait_sock.h>
 #include <net/ip.h>

 /* Must be called with locally disabled BHs. */
 void __inet_twsk_kill(struct inet_timewait_sock *tw, struct inet_hashinfo *hashinfo)
 {
 	struct inet_bind_hashbucket *bhead;
 	struct inet_bind_bucket *tb;
 	/* Unlink from established hashes. */
 	struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, tw->tw_hash);

 	write_lock(&ehead->lock);
 	if (hlist_unhashed(&tw->tw_node)) {
 		write_unlock(&ehead->lock);
 		return;
 	}
 	__hlist_del(&tw->tw_node);
 	sk_node_init(&tw->tw_node);
 	write_unlock(&ehead->lock);

 	/* Disassociate with bind bucket. */
 	bhead = &hashinfo->bhash[inet_bhashfn(tw->tw_num, hashinfo->bhash_size)];
 	spin_lock(&bhead->lock);
 	tb = tw->tw_tb;
 	__hlist_del(&tw->tw_bind_node);
 	tw->tw_tb = NULL;
 	inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
 	spin_unlock(&bhead->lock);
 #ifdef SOCK_REFCNT_DEBUG
 	if (atomic_read(&tw->tw_refcnt) != 1) {
 		printk(KERN_DEBUG "%s timewait_sock %p refcnt=%d\n",
 		       tw->tw_prot->name, tw, atomic_read(&tw->tw_refcnt));
 	}
 #endif
 	inet_twsk_put(tw);
 }

 EXPORT_SYMBOL_GPL(__inet_twsk_kill);

 /*
  * 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);
 	struct inet_bind_hashbucket *bhead;
 	/* 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(inet->num, hashinfo->bhash_size)];
 	spin_lock(&bhead->lock);
 	tw->tw_tb = icsk->icsk_bind_hash;
 	BUG_TRAP(icsk->icsk_bind_hash);
 	inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
 	spin_unlock(&bhead->lock);

 	write_lock(&ehead->lock);

 	/* Step 2: Remove SK from established hash. */
 	if (__sk_del_node_init(sk))
 		sock_prot_dec_use(sk->sk_prot);

 	/* Step 3: Hash TW into TIMEWAIT chain. */
 	inet_twsk_add_node(tw, &ehead->twchain);
 	atomic_inc(&tw->tw_refcnt);

 	write_unlock(&ehead->lock);
 }

 EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);

 struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk, const int state)
 {
 	struct inet_timewait_sock *tw =
 		kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
 				 GFP_ATOMIC);
 	if (tw != NULL) {
 		const struct inet_sock *inet = inet_sk(sk);

 		/* Give us an identity. */
 		tw->tw_daddr	    = inet->daddr;
 		tw->tw_rcv_saddr    = inet->rcv_saddr;
 		tw->tw_bound_dev_if = sk->sk_bound_dev_if;
 		tw->tw_num	    = inet->num;
 		tw->tw_state	    = TCP_TIME_WAIT;
 		tw->tw_substate	    = state;
 		tw->tw_sport	    = inet->sport;
 		tw->tw_dport	    = inet->dport;
 		tw->tw_family	    = sk->sk_family;
 		tw->tw_reuse	    = sk->sk_reuse;
 		tw->tw_hash	    = sk->sk_hash;
 		tw->tw_ipv6only	    = 0;
 		tw->tw_prot	    = sk->sk_prot_creator;
 		atomic_set(&tw->tw_refcnt, 1);
 		inet_twsk_dead_node_init(tw);
 		__module_get(tw->tw_prot->owner);
 	}

 	return tw;
 }

 EXPORT_SYMBOL_GPL(inet_twsk_alloc);

 /* Returns non-zero if quota exceeded.  */
 static int inet_twdr_do_twkill_work(struct inet_timewait_death_row *twdr,
 				    const int slot)
 {
 	struct inet_timewait_sock *tw;
 	struct hlist_node *node;
 	unsigned int killed;
 	int ret;

 	/* NOTE: compare this to previous version where lock
 	 * was released after detaching chain. It was racy,
 	 * because tw buckets are scheduled in not serialized context
 	 * in 2.3 (with netfilter), and with softnet it is common, because
 	 * soft irqs are not sequenced.
 	 */
 	killed = 0;
 	ret = 0;
 rescan:
 	inet_twsk_for_each_inmate(tw, node, &twdr->cells[slot]) {
 		__inet_twsk_del_dead_node(tw);
 		spin_unlock(&twdr->death_lock);
 		__inet_twsk_kill(tw, twdr->hashinfo);
 		inet_twsk_put(tw);
 		killed++;
 		spin_lock(&twdr->death_lock);
 		if (killed > INET_TWDR_TWKILL_QUOTA) {
 			ret = 1;
 			break;
 		}

 		/* While we dropped twdr->death_lock, another cpu may have
 		 * killed off the next TW bucket in the list, therefore
 		 * do a fresh re-read of the hlist head node with the
 		 * lock reacquired.  We still use the hlist traversal
 		 * macro in order to get the prefetches.
 		 */
 		goto rescan;
 	}

 	twdr->tw_count -= killed;
 	NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITED, killed);

 	return ret;
 }

 void inet_twdr_hangman(unsigned long data)
 {
 	struct inet_timewait_death_row *twdr;
 	int unsigned need_timer;

 	twdr = (struct inet_timewait_death_row *)data;
 	spin_lock(&twdr->death_lock);

 	if (twdr->tw_count == 0)
 		goto out;

 	need_timer = 0;
 	if (inet_twdr_do_twkill_work(twdr, twdr->slot)) {
 		twdr->thread_slots |= (1 << twdr->slot);
 		schedule_work(&twdr->twkill_work);
 		need_timer = 1;
 	} else {
 		/* We purged the entire slot, anything left?  */
 		if (twdr->tw_count)
 			need_timer = 1;
 	}
 	twdr->slot = ((twdr->slot + 1) & (INET_TWDR_TWKILL_SLOTS - 1));
 	if (need_timer)
 		mod_timer(&twdr->tw_timer, jiffies + twdr->period);
 out:
 	spin_unlock(&twdr->death_lock);
 }

 EXPORT_SYMBOL_GPL(inet_twdr_hangman);

 extern void twkill_slots_invalid(void);

 void inet_twdr_twkill_work(struct work_struct *work)
 {
 	struct inet_timewait_death_row *twdr =
 		container_of(work, struct inet_timewait_death_row, twkill_work);
 	int i;

 	if ((INET_TWDR_TWKILL_SLOTS - 1) > (sizeof(twdr->thread_slots) * 8))
 		twkill_slots_invalid();

 	while (twdr->thread_slots) {
 		spin_lock_bh(&twdr->death_lock);
 		for (i = 0; i < INET_TWDR_TWKILL_SLOTS; i++) {
 			if (!(twdr->thread_slots & (1 << i)))
 				continue;

 			while (inet_twdr_do_twkill_work(twdr, i) != 0) {
 				if (need_resched()) {
 					spin_unlock_bh(&twdr->death_lock);
 					schedule();
 					spin_lock_bh(&twdr->death_lock);
 				}
 			}

 			twdr->thread_slots &= ~(1 << i);
 		}
 		spin_unlock_bh(&twdr->death_lock);
 	}
 }

 EXPORT_SYMBOL_GPL(inet_twdr_twkill_work);

 /* 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. */
 void inet_twsk_deschedule(struct inet_timewait_sock *tw,
 			  struct inet_timewait_death_row *twdr)
 {
 	spin_lock(&twdr->death_lock);
 	if (inet_twsk_del_dead_node(tw)) {
 		inet_twsk_put(tw);
 		if (--twdr->tw_count == 0)
 			del_timer(&twdr->tw_timer);
 	}
 	spin_unlock(&twdr->death_lock);
 	__inet_twsk_kill(tw, twdr->hashinfo);
 }

 EXPORT_SYMBOL(inet_twsk_deschedule);

 void inet_twsk_schedule(struct inet_timewait_sock *tw,
 		       struct inet_timewait_death_row *twdr,
 		       const int timeo, const int timewait_len)
 {
 	struct hlist_head *list;
 	int slot;

 	/* 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.
 	 */
 	slot = (timeo + (1 << INET_TWDR_RECYCLE_TICK) - 1) >> INET_TWDR_RECYCLE_TICK;

 	spin_lock(&twdr->death_lock);

 	/* Unlink it, if it was scheduled */
 	if (inet_twsk_del_dead_node(tw))
 		twdr->tw_count--;
 	else
 		atomic_inc(&tw->tw_refcnt);

 	if (slot >= INET_TWDR_RECYCLE_SLOTS) {
 		/* Schedule to slow timer */
 		if (timeo >= timewait_len) {
 			slot = INET_TWDR_TWKILL_SLOTS - 1;
 		} else {
 			slot = (timeo + twdr->period - 1) / twdr->period;
 			if (slot >= INET_TWDR_TWKILL_SLOTS)
 				slot = INET_TWDR_TWKILL_SLOTS - 1;
 		}
 		tw->tw_ttd = jiffies + timeo;
 		slot = (twdr->slot + slot) & (INET_TWDR_TWKILL_SLOTS - 1);
 		list = &twdr->cells[slot];
 	} else {
 		tw->tw_ttd = jiffies + (slot << INET_TWDR_RECYCLE_TICK);

 		if (twdr->twcal_hand < 0) {
 			twdr->twcal_hand = 0;
 			twdr->twcal_jiffie = jiffies;
 			twdr->twcal_timer.expires = twdr->twcal_jiffie +
 					      (slot << INET_TWDR_RECYCLE_TICK);
 			add_timer(&twdr->twcal_timer);
 		} else {
 			if (time_after(twdr->twcal_timer.expires,
 				       jiffies + (slot << INET_TWDR_RECYCLE_TICK)))
 				mod_timer(&twdr->twcal_timer,
 					  jiffies + (slot << INET_TWDR_RECYCLE_TICK));
 			slot = (twdr->twcal_hand + slot) & (INET_TWDR_RECYCLE_SLOTS - 1);
 		}
 		list = &twdr->twcal_row[slot];
 	}

 	hlist_add_head(&tw->tw_death_node, list);

 	if (twdr->tw_count++ == 0)
 		mod_timer(&twdr->tw_timer, jiffies + twdr->period);
 	spin_unlock(&twdr->death_lock);
 }

 EXPORT_SYMBOL_GPL(inet_twsk_schedule);

 void inet_twdr_twcal_tick(unsigned long data)
 {
 	struct inet_timewait_death_row *twdr;
 	int n, slot;
 	unsigned long j;
 	unsigned long now = jiffies;
 	int killed = 0;
 	int adv = 0;

 	twdr = (struct inet_timewait_death_row *)data;

 	spin_lock(&twdr->death_lock);
 	if (twdr->twcal_hand < 0)
 		goto out;

 	slot = twdr->twcal_hand;
 	j = twdr->twcal_jiffie;

 	for (n = 0; n < INET_TWDR_RECYCLE_SLOTS; n++) {
 		if (time_before_eq(j, now)) {
 			struct hlist_node *node, *safe;
 			struct inet_timewait_sock *tw;

 			inet_twsk_for_each_inmate_safe(tw, node, safe,
 						       &twdr->twcal_row[slot]) {
 				__inet_twsk_del_dead_node(tw);
 				__inet_twsk_kill(tw, twdr->hashinfo);
 				inet_twsk_put(tw);
 				killed++;
 			}
 		} else {
 			if (!adv) {
 				adv = 1;
 				twdr->twcal_jiffie = j;
 				twdr->twcal_hand = slot;
 			}

 			if (!hlist_empty(&twdr->twcal_row[slot])) {
 				mod_timer(&twdr->twcal_timer, j);
 				goto out;
 			}
 		}
 		j += 1 << INET_TWDR_RECYCLE_TICK;
 		slot = (slot + 1) & (INET_TWDR_RECYCLE_SLOTS - 1);
 	}
 	twdr->twcal_hand = -1;

 out:
 	if ((twdr->tw_count -= killed) == 0)
 		del_timer(&twdr->tw_timer);
 	NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITKILLED, killed);
 	spin_unlock(&twdr->death_lock);
 }

 EXPORT_SYMBOL_GPL(inet_twdr_twcal_tick);
	/*
	* 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 <net/inet_hashtables.h>
	#include <net/inet_timewait_sock.h>
	#include <net/ip.h>

	/* Must be called with locally disabled BHs. */
	void __inet_twsk_kill(struct inet_timewait_sock tw, struct inet_hashinfo hashinfo)
	{
	struct inet_bind_hashbucket *bhead;
	struct inet_bind_bucket *tb;
	/* Unlink from established hashes. */
	struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, tw->tw_hash);

	write_lock(&ehead->lock);
	if (hlist_unhashed(&tw->tw_node)) {
	write_unlock(&ehead->lock);
	return;
	}
	__hlist_del(&tw->tw_node);
	sk_node_init(&tw->tw_node);
	write_unlock(&ehead->lock);

	/* Disassociate with bind bucket. */
	bhead = &hashinfo->bhash[inet_bhashfn(tw->tw_num, hashinfo->bhash_size)];
	spin_lock(&bhead->lock);
	tb = tw->tw_tb;
	__hlist_del(&tw->tw_bind_node);
	tw->tw_tb = NULL;
	inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
	spin_unlock(&bhead->lock);
	#ifdef SOCK_REFCNT_DEBUG
	if (atomic_read(&tw->tw_refcnt) != 1) {
	printk(KERN_DEBUG "%s timewait_sock %p refcnt=%d\n",
	tw->tw_prot->name, tw, atomic_read(&tw->tw_refcnt));
	}
	#endif
	inet_twsk_put(tw);
	}

	EXPORT_SYMBOL_GPL(__inet_twsk_kill);

	/*
	* 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);
	struct inet_bind_hashbucket *bhead;
	/* 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(inet->num, hashinfo->bhash_size)];
	spin_lock(&bhead->lock);
	tw->tw_tb = icsk->icsk_bind_hash;
	BUG_TRAP(icsk->icsk_bind_hash);
	inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
	spin_unlock(&bhead->lock);

	write_lock(&ehead->lock);

	/* Step 2: Remove SK from established hash. */
	if (__sk_del_node_init(sk))
	sock_prot_dec_use(sk->sk_prot);

	/* Step 3: Hash TW into TIMEWAIT chain. */
	inet_twsk_add_node(tw, &ehead->twchain);
	atomic_inc(&tw->tw_refcnt);

	write_unlock(&ehead->lock);
	}

	EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);

	struct inet_timewait_sock inet_twsk_alloc(const struct sock sk, const int state)
	{
	struct inet_timewait_sock *tw =
	kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
	GFP_ATOMIC);
	if (tw != NULL) {
	const struct inet_sock *inet = inet_sk(sk);

	/* Give us an identity. */
	tw->tw_daddr = inet->daddr;
	tw->tw_rcv_saddr = inet->rcv_saddr;
	tw->tw_bound_dev_if = sk->sk_bound_dev_if;
	tw->tw_num = inet->num;
	tw->tw_state = TCP_TIME_WAIT;
	tw->tw_substate = state;
	tw->tw_sport = inet->sport;
	tw->tw_dport = inet->dport;
	tw->tw_family = sk->sk_family;
	tw->tw_reuse = sk->sk_reuse;
	tw->tw_hash = sk->sk_hash;
	tw->tw_ipv6only = 0;
	tw->tw_prot = sk->sk_prot_creator;
	atomic_set(&tw->tw_refcnt, 1);
	inet_twsk_dead_node_init(tw);
	__module_get(tw->tw_prot->owner);
	}

	return tw;
	}

	EXPORT_SYMBOL_GPL(inet_twsk_alloc);

	/* Returns non-zero if quota exceeded. */
	static int inet_twdr_do_twkill_work(struct inet_timewait_death_row *twdr,
	const int slot)
	{
	struct inet_timewait_sock *tw;
	struct hlist_node *node;
	unsigned int killed;
	int ret;

	/* NOTE: compare this to previous version where lock
	* was released after detaching chain. It was racy,
	* because tw buckets are scheduled in not serialized context
	* in 2.3 (with netfilter), and with softnet it is common, because
	* soft irqs are not sequenced.
	*/
	killed = 0;
	ret = 0;
	rescan:
	inet_twsk_for_each_inmate(tw, node, &twdr->cells[slot]) {
	__inet_twsk_del_dead_node(tw);
	spin_unlock(&twdr->death_lock);
	__inet_twsk_kill(tw, twdr->hashinfo);
	inet_twsk_put(tw);
	killed++;
	spin_lock(&twdr->death_lock);
	if (killed > INET_TWDR_TWKILL_QUOTA) {
	ret = 1;
	break;
	}

	/* While we dropped twdr->death_lock, another cpu may have
	* killed off the next TW bucket in the list, therefore
	* do a fresh re-read of the hlist head node with the
	* lock reacquired. We still use the hlist traversal
	* macro in order to get the prefetches.
	*/
	goto rescan;
	}

	twdr->tw_count -= killed;
	NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITED, killed);

	return ret;
	}

	void inet_twdr_hangman(unsigned long data)
	{
	struct inet_timewait_death_row *twdr;
	int unsigned need_timer;

	twdr = (struct inet_timewait_death_row *)data;
	spin_lock(&twdr->death_lock);

	if (twdr->tw_count == 0)
	goto out;

	need_timer = 0;
	if (inet_twdr_do_twkill_work(twdr, twdr->slot)) {
	twdr->thread_slots \|= (1 << twdr->slot);
	schedule_work(&twdr->twkill_work);
	need_timer = 1;
	} else {
	/* We purged the entire slot, anything left? */
	if (twdr->tw_count)
	need_timer = 1;
	}
	twdr->slot = ((twdr->slot + 1) & (INET_TWDR_TWKILL_SLOTS - 1));
	if (need_timer)
	mod_timer(&twdr->tw_timer, jiffies + twdr->period);
	out:
	spin_unlock(&twdr->death_lock);
	}

	EXPORT_SYMBOL_GPL(inet_twdr_hangman);

	extern void twkill_slots_invalid(void);

	void inet_twdr_twkill_work(struct work_struct *work)
	{
	struct inet_timewait_death_row *twdr =
	container_of(work, struct inet_timewait_death_row, twkill_work);
	int i;

	if ((INET_TWDR_TWKILL_SLOTS - 1) > (sizeof(twdr->thread_slots) * 8))
	twkill_slots_invalid();

	while (twdr->thread_slots) {
	spin_lock_bh(&twdr->death_lock);
	for (i = 0; i < INET_TWDR_TWKILL_SLOTS; i++) {
	if (!(twdr->thread_slots & (1 << i)))
	continue;

	while (inet_twdr_do_twkill_work(twdr, i) != 0) {
	if (need_resched()) {
	spin_unlock_bh(&twdr->death_lock);
	schedule();
	spin_lock_bh(&twdr->death_lock);
	}
	}

	twdr->thread_slots &= ~(1 << i);
	}
	spin_unlock_bh(&twdr->death_lock);
	}
	}

	EXPORT_SYMBOL_GPL(inet_twdr_twkill_work);

	/* 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. */
	void inet_twsk_deschedule(struct inet_timewait_sock *tw,
	struct inet_timewait_death_row *twdr)
	{
	spin_lock(&twdr->death_lock);
	if (inet_twsk_del_dead_node(tw)) {
	inet_twsk_put(tw);
	if (--twdr->tw_count == 0)
	del_timer(&twdr->tw_timer);
	}
	spin_unlock(&twdr->death_lock);
	__inet_twsk_kill(tw, twdr->hashinfo);
	}

	EXPORT_SYMBOL(inet_twsk_deschedule);

	void inet_twsk_schedule(struct inet_timewait_sock *tw,
	struct inet_timewait_death_row *twdr,
	const int timeo, const int timewait_len)
	{
	struct hlist_head *list;
	int slot;

	/* 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.
	*/
	slot = (timeo + (1 << INET_TWDR_RECYCLE_TICK) - 1) >> INET_TWDR_RECYCLE_TICK;

	spin_lock(&twdr->death_lock);

	/* Unlink it, if it was scheduled */
	if (inet_twsk_del_dead_node(tw))
	twdr->tw_count--;
	else
	atomic_inc(&tw->tw_refcnt);

	if (slot >= INET_TWDR_RECYCLE_SLOTS) {
	/* Schedule to slow timer */
	if (timeo >= timewait_len) {
	slot = INET_TWDR_TWKILL_SLOTS - 1;
	} else {
	slot = (timeo + twdr->period - 1) / twdr->period;
	if (slot >= INET_TWDR_TWKILL_SLOTS)
	slot = INET_TWDR_TWKILL_SLOTS - 1;
	}
	tw->tw_ttd = jiffies + timeo;
	slot = (twdr->slot + slot) & (INET_TWDR_TWKILL_SLOTS - 1);
	list = &twdr->cells[slot];
	} else {
	tw->tw_ttd = jiffies + (slot << INET_TWDR_RECYCLE_TICK);

	if (twdr->twcal_hand < 0) {
	twdr->twcal_hand = 0;
	twdr->twcal_jiffie = jiffies;
	twdr->twcal_timer.expires = twdr->twcal_jiffie +
	(slot << INET_TWDR_RECYCLE_TICK);
	add_timer(&twdr->twcal_timer);
	} else {
	if (time_after(twdr->twcal_timer.expires,
	jiffies + (slot << INET_TWDR_RECYCLE_TICK)))
	mod_timer(&twdr->twcal_timer,
	jiffies + (slot << INET_TWDR_RECYCLE_TICK));
	slot = (twdr->twcal_hand + slot) & (INET_TWDR_RECYCLE_SLOTS - 1);
	}
	list = &twdr->twcal_row[slot];
	}

	hlist_add_head(&tw->tw_death_node, list);

	if (twdr->tw_count++ == 0)
	mod_timer(&twdr->tw_timer, jiffies + twdr->period);
	spin_unlock(&twdr->death_lock);
	}

	EXPORT_SYMBOL_GPL(inet_twsk_schedule);

	void inet_twdr_twcal_tick(unsigned long data)
	{
	struct inet_timewait_death_row *twdr;
	int n, slot;
	unsigned long j;
	unsigned long now = jiffies;
	int killed = 0;
	int adv = 0;

	twdr = (struct inet_timewait_death_row *)data;

	spin_lock(&twdr->death_lock);
	if (twdr->twcal_hand < 0)
	goto out;

	slot = twdr->twcal_hand;
	j = twdr->twcal_jiffie;

	for (n = 0; n < INET_TWDR_RECYCLE_SLOTS; n++) {
	if (time_before_eq(j, now)) {
	struct hlist_node node, safe;
	struct inet_timewait_sock *tw;

	inet_twsk_for_each_inmate_safe(tw, node, safe,
	&twdr->twcal_row[slot]) {
	__inet_twsk_del_dead_node(tw);
	__inet_twsk_kill(tw, twdr->hashinfo);
	inet_twsk_put(tw);
	killed++;
	}
	} else {
	if (!adv) {
	adv = 1;
	twdr->twcal_jiffie = j;
	twdr->twcal_hand = slot;
	}

	if (!hlist_empty(&twdr->twcal_row[slot])) {
	mod_timer(&twdr->twcal_timer, j);
	goto out;
	}
	}
	j += 1 << INET_TWDR_RECYCLE_TICK;
	slot = (slot + 1) & (INET_TWDR_RECYCLE_SLOTS - 1);
	}
	twdr->twcal_hand = -1;

	out:
	if ((twdr->tw_count -= killed) == 0)
	del_timer(&twdr->tw_timer);
	NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITKILLED, killed);
	spin_unlock(&twdr->death_lock);
	}

	EXPORT_SYMBOL_GPL(inet_twdr_twcal_tick);