Patchwork [3/3] net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls

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Submitter Eric Dumazet
Date Nov. 13, 2008, 1:15 p.m.
Message ID <491C2873.60004@cosmosbay.com>
Download mbox | patch
Permalink /patch/8569/
State Accepted
Delegated to: David Miller
Headers show

Comments

Eric Dumazet - Nov. 13, 2008, 1:15 p.m.
RCU was added to UDP lookups, using a fast infrastructure :
- sockets kmem_cache use SLAB_DESTROY_BY_RCU and dont pay the
  price of call_rcu() at freeing time.
- hlist_nulls permits to use few memory barriers.

This patch uses same infrastructure for TCP/DCCP established
and timewait sockets.

Thanks to SLAB_DESTROY_BY_RCU, no slowdown for applications
using short lived TCP connections. A followup patch, converting
rwlocks to spinlocks will even speedup this case.

__inet_lookup_established() is pretty fast now we dont have to
dirty a contended cache line (read_lock/read_unlock)

Only established and timewait hashtable are converted to RCU
(bind table and listen table are still using traditional locking)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
---
 include/net/inet_hashtables.h    |    4 -
 include/net/inet_timewait_sock.h |   10 +--
 net/core/sock.c                  |    4 +
 net/dccp/ipv4.c                  |    1
 net/dccp/ipv6.c                  |    1
 net/dccp/proto.c                 |    4 -
 net/ipv4/inet_diag.c             |    6 +-
 net/ipv4/inet_hashtables.c       |   78 ++++++++++++++++++++---------
 net/ipv4/inet_timewait_sock.c    |   26 +++++----
 net/ipv4/tcp.c                   |    4 -
 net/ipv4/tcp_ipv4.c              |   25 ++++-----
 net/ipv6/inet6_hashtables.c      |   70 +++++++++++++++++---------
 net/ipv6/tcp_ipv6.c              |    1
 13 files changed, 150 insertions(+), 84 deletions(-)
Peter Zijlstra - Nov. 13, 2008, 1:34 p.m.
On Thu, 2008-11-13 at 14:15 +0100, Eric Dumazet wrote:
> +begin:
> +       sk_nulls_for_each_rcu(sk, node, &head->chain) {
>                 if (INET_MATCH(sk, net, hash, acookie,
> +                                       saddr, daddr, ports, dif)) {
> +                       if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
> +                               goto begintw;
> +                       if (unlikely(!INET_MATCH(sk, net, hash, acookie,
> +                               saddr, daddr, ports, dif))) {
> +                               sock_put(sk);
> +                               goto begin;
> +                       }

This is the validation step that verifies the race opened by using
SLAB_DESTROY_BY_RCU, right?

Does it make sense to add a little comment to these validation steps to
keep people on their toes and aware of the trickery?

> +                       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 begin;
>  

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Eric Dumazet - Nov. 13, 2008, 1:51 p.m.
Peter Zijlstra a écrit :
> On Thu, 2008-11-13 at 14:15 +0100, Eric Dumazet wrote:
>> +begin:
>> +       sk_nulls_for_each_rcu(sk, node, &head->chain) {
>>                 if (INET_MATCH(sk, net, hash, acookie,
>> +                                       saddr, daddr, ports, dif)) {
>> +                       if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
>> +                               goto begintw;
>> +                       if (unlikely(!INET_MATCH(sk, net, hash, acookie,
>> +                               saddr, daddr, ports, dif))) {
>> +                               sock_put(sk);
>> +                               goto begin;
>> +                       }
> 
> This is the validation step that verifies the race opened by using
> SLAB_DESTROY_BY_RCU, right?

The atomic_inc_not_zero() is not related to SLAB_DESTROY_BY_RCU but
classic RCU lookup. A writer can delete the item right before we try to use it.

Next step is necessary in case the deleted item was re-allocated and inserted
in a hash chain (this one or another one, it doesnt matter). In this case,
previous atomic_inc_not_zero test will succeed. So we must check again the item
we selected (and refcounted) is the one we were searching.

So yes, this bit should be documented, since SLAB_DESTROY_BY_RCU is
not really used in linux kernel at this moment.


> 
> Does it make sense to add a little comment to these validation steps to
> keep people on their toes and aware of the trickery?

Yes, you are right.

Thanks


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Christoph Lameter - Nov. 13, 2008, 2:08 p.m.
On Thu, 13 Nov 2008, Eric Dumazet wrote:

> So yes, this bit should be documented, since SLAB_DESTROY_BY_RCU is
> not really used in linux kernel at this moment.

It is used for the anonymous vmas. That is the purpose that Hugh
introduced it for since he saw regression if he would use straight rcu
freeing. See mm/rmap.c. SLAB_DESTROY_BY_RCU a pretty strange way of
using RCU and slab so it should always be documented in detail.

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Peter Zijlstra - Nov. 13, 2008, 2:22 p.m.
On Thu, 2008-11-13 at 14:51 +0100, Eric Dumazet wrote:
> Peter Zijlstra a écrit :
> > On Thu, 2008-11-13 at 14:15 +0100, Eric Dumazet wrote:
> >> +begin:
> >> +       sk_nulls_for_each_rcu(sk, node, &head->chain) {
> >>                 if (INET_MATCH(sk, net, hash, acookie,
> >> +                                       saddr, daddr, ports, dif)) {
> >> +                       if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
> >> +                               goto begintw;
> >> +                       if (unlikely(!INET_MATCH(sk, net, hash, acookie,
> >> +                               saddr, daddr, ports, dif))) {
> >> +                               sock_put(sk);
> >> +                               goto begin;
> >> +                       }
> > 
> > This is the validation step that verifies the race opened by using
> > SLAB_DESTROY_BY_RCU, right?
> 
> The atomic_inc_not_zero() is not related to SLAB_DESTROY_BY_RCU but
> classic RCU lookup. A writer can delete the item right before we try to use it.

Yeah, its to stabilize the current situation.

> Next step is necessary in case the deleted item was re-allocated and inserted
> in a hash chain (this one or another one, it doesnt matter). In this case,
> previous atomic_inc_not_zero test will succeed. So we must check again the item
> we selected (and refcounted) is the one we were searching.
> 
> So yes, this bit should be documented, since SLAB_DESTROY_BY_RCU is
> not really used in linux kernel at this moment.

We have one user, anon_vma, and one thing that is very nearly identical
the lockless pagecache.

See page_cache_get_speculative() and find_get_page(). The pagecache gets
away with this due to the simple fact that the page frames are never
freed.

Hmm, I once wrote a comment to go with SLAB_DESTROY_BY_RCU, which seems
to have gotten lost... /me goes dig.

Found it:  http://lkml.org/lkml/2008/4/2/143

I guess I'd better re-submit that..

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Christoph Lameter - Nov. 13, 2008, 2:27 p.m.
On Thu, 13 Nov 2008, Peter Zijlstra wrote:

> Found it:  http://lkml.org/lkml/2008/4/2/143
>
> I guess I'd better re-submit that..

Looks good. CC Pekka and he will merge it.


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Paul E. McKenney - Nov. 19, 2008, 5:53 p.m.
On Thu, Nov 13, 2008 at 02:15:31PM +0100, Eric Dumazet wrote:
> RCU was added to UDP lookups, using a fast infrastructure :
> - sockets kmem_cache use SLAB_DESTROY_BY_RCU and dont pay the
>  price of call_rcu() at freeing time.
> - hlist_nulls permits to use few memory barriers.
>
> This patch uses same infrastructure for TCP/DCCP established
> and timewait sockets.
>
> Thanks to SLAB_DESTROY_BY_RCU, no slowdown for applications
> using short lived TCP connections. A followup patch, converting
> rwlocks to spinlocks will even speedup this case.
>
> __inet_lookup_established() is pretty fast now we dont have to
> dirty a contended cache line (read_lock/read_unlock)
>
> Only established and timewait hashtable are converted to RCU
> (bind table and listen table are still using traditional locking)

Looks good to me!

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
> ---
> include/net/inet_hashtables.h    |    4 -
> include/net/inet_timewait_sock.h |   10 +--
> net/core/sock.c                  |    4 +
> net/dccp/ipv4.c                  |    1
> net/dccp/ipv6.c                  |    1
> net/dccp/proto.c                 |    4 -
> net/ipv4/inet_diag.c             |    6 +-
> net/ipv4/inet_hashtables.c       |   78 ++++++++++++++++++++---------
> net/ipv4/inet_timewait_sock.c    |   26 +++++----
> net/ipv4/tcp.c                   |    4 -
> net/ipv4/tcp_ipv4.c              |   25 ++++-----
> net/ipv6/inet6_hashtables.c      |   70 +++++++++++++++++---------
> net/ipv6/tcp_ipv6.c              |    1
> 13 files changed, 150 insertions(+), 84 deletions(-)

> diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
> index cb31fbf..4818960 100644
> --- a/include/net/inet_hashtables.h
> +++ b/include/net/inet_hashtables.h
> @@ -41,8 +41,8 @@
>   * I'll experiment with dynamic table growth later.
>   */
>  struct inet_ehash_bucket {
> -	struct hlist_head chain;
> -	struct hlist_head twchain;
> +	struct hlist_nulls_head chain;
> +	struct hlist_nulls_head twchain;
>  };
> 
>  /* There are a few simple rules, which allow for local port reuse by
> diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h
> index 80e4977..4b8ece2 100644
> --- a/include/net/inet_timewait_sock.h
> +++ b/include/net/inet_timewait_sock.h
> @@ -110,7 +110,7 @@ struct inet_timewait_sock {
>  #define tw_state		__tw_common.skc_state
>  #define tw_reuse		__tw_common.skc_reuse
>  #define tw_bound_dev_if		__tw_common.skc_bound_dev_if
> -#define tw_node			__tw_common.skc_node
> +#define tw_node			__tw_common.skc_nulls_node
>  #define tw_bind_node		__tw_common.skc_bind_node
>  #define tw_refcnt		__tw_common.skc_refcnt
>  #define tw_hash			__tw_common.skc_hash
> @@ -137,10 +137,10 @@ struct inet_timewait_sock {
>  	struct hlist_node	tw_death_node;
>  };
> 
> -static inline void inet_twsk_add_node(struct inet_timewait_sock *tw,
> -				      struct hlist_head *list)
> +static inline void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
> +				      struct hlist_nulls_head *list)
>  {
> -	hlist_add_head(&tw->tw_node, list);
> +	hlist_nulls_add_head_rcu(&tw->tw_node, list);
>  }
> 
>  static inline void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
> @@ -175,7 +175,7 @@ static inline int inet_twsk_del_dead_node(struct inet_timewait_sock *tw)
>  }
> 
>  #define inet_twsk_for_each(tw, node, head) \
> -	hlist_for_each_entry(tw, node, head, tw_node)
> +	hlist_nulls_for_each_entry(tw, node, head, tw_node)
> 
>  #define inet_twsk_for_each_inmate(tw, node, jail) \
>  	hlist_for_each_entry(tw, node, jail, tw_death_node)
> diff --git a/net/core/sock.c b/net/core/sock.c
> index ded1eb5..38de9c3 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2082,7 +2082,9 @@ int proto_register(struct proto *prot, int alloc_slab)
>  			prot->twsk_prot->twsk_slab =
>  				kmem_cache_create(timewait_sock_slab_name,
>  						  prot->twsk_prot->twsk_obj_size,
> -						  0, SLAB_HWCACHE_ALIGN,
> +						  0,
> +						  SLAB_HWCACHE_ALIGN |
> +							prot->slab_flags,
>  						  NULL);
>  			if (prot->twsk_prot->twsk_slab == NULL)
>  				goto out_free_timewait_sock_slab_name;
> diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
> index 528baa2..d1dd952 100644
> --- a/net/dccp/ipv4.c
> +++ b/net/dccp/ipv4.c
> @@ -938,6 +938,7 @@ static struct proto dccp_v4_prot = {
>  	.orphan_count		= &dccp_orphan_count,
>  	.max_header		= MAX_DCCP_HEADER,
>  	.obj_size		= sizeof(struct dccp_sock),
> +	.slab_flags		= SLAB_DESTROY_BY_RCU,
>  	.rsk_prot		= &dccp_request_sock_ops,
>  	.twsk_prot		= &dccp_timewait_sock_ops,
>  	.h.hashinfo		= &dccp_hashinfo,
> diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
> index 4aa1148..f033e84 100644
> --- a/net/dccp/ipv6.c
> +++ b/net/dccp/ipv6.c
> @@ -1140,6 +1140,7 @@ static struct proto dccp_v6_prot = {
>  	.orphan_count	   = &dccp_orphan_count,
>  	.max_header	   = MAX_DCCP_HEADER,
>  	.obj_size	   = sizeof(struct dccp6_sock),
> +	.slab_flags	   = SLAB_DESTROY_BY_RCU,
>  	.rsk_prot	   = &dccp6_request_sock_ops,
>  	.twsk_prot	   = &dccp6_timewait_sock_ops,
>  	.h.hashinfo	   = &dccp_hashinfo,
> diff --git a/net/dccp/proto.c b/net/dccp/proto.c
> index 46cb349..1117d4d 100644
> --- a/net/dccp/proto.c
> +++ b/net/dccp/proto.c
> @@ -1090,8 +1090,8 @@ static int __init dccp_init(void)
>  	}
> 
>  	for (i = 0; i < dccp_hashinfo.ehash_size; i++) {
> -		INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].chain);
> -		INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].twchain);
> +		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))
> diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
> index 564230d..41b3672 100644
> --- a/net/ipv4/inet_diag.c
> +++ b/net/ipv4/inet_diag.c
> @@ -778,18 +778,19 @@ skip_listen_ht:
>  		struct inet_ehash_bucket *head = &hashinfo->ehash[i];
>  		rwlock_t *lock = inet_ehash_lockp(hashinfo, i);
>  		struct sock *sk;
> -		struct hlist_node *node;
> +		struct hlist_nulls_node *node;
> 
>  		num = 0;
> 
> -		if (hlist_empty(&head->chain) && hlist_empty(&head->twchain))
> +		if (hlist_nulls_empty(&head->chain) &&
> +			hlist_nulls_empty(&head->twchain))
>  			continue;
> 
>  		if (i > s_i)
>  			s_num = 0;
> 
>  		read_lock_bh(lock);
> -		sk_for_each(sk, node, &head->chain) {
> +		sk_nulls_for_each(sk, node, &head->chain) {
>  			struct inet_sock *inet = inet_sk(sk);
> 
>  			if (num < s_num)
> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> index be41ebb..fd269cf 100644
> --- a/net/ipv4/inet_hashtables.c
> +++ b/net/ipv4/inet_hashtables.c
> @@ -223,35 +223,65 @@ struct sock * __inet_lookup_established(struct net *net,
>  	INET_ADDR_COOKIE(acookie, saddr, daddr)
>  	const __portpair ports = INET_COMBINED_PORTS(sport, hnum);
>  	struct sock *sk;
> -	const struct hlist_node *node;
> +	const struct hlist_nulls_node *node;
>  	/* Optimize here for direct hit, only listening connections can
>  	 * have wildcards anyways.
>  	 */
>  	unsigned int hash = inet_ehashfn(net, daddr, hnum, saddr, sport);
> -	struct inet_ehash_bucket *head = inet_ehash_bucket(hashinfo, hash);
> -	rwlock_t *lock = inet_ehash_lockp(hashinfo, hash);
> +	unsigned int slot = hash & (hashinfo->ehash_size - 1);
> +	struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
> 
> -	prefetch(head->chain.first);
> -	read_lock(lock);
> -	sk_for_each(sk, node, &head->chain) {
> +	rcu_read_lock();
> +begin:
> +	sk_nulls_for_each_rcu(sk, node, &head->chain) {
>  		if (INET_MATCH(sk, net, hash, acookie,
> -					saddr, daddr, ports, dif))
> -			goto hit; /* You sunk my battleship! */
> +					saddr, daddr, ports, dif)) {
> +			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
> +				goto begintw;
> +			if (unlikely(!INET_MATCH(sk, net, hash, acookie,
> +				saddr, daddr, ports, dif))) {
> +				sock_put(sk);
> +				goto begin;
> +			}
> +			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 begin;
> 
> +begintw:
>  	/* Must check for a TIME_WAIT'er before going to listener hash. */
> -	sk_for_each(sk, node, &head->twchain) {
> +	sk_nulls_for_each_rcu(sk, node, &head->twchain) {
>  		if (INET_TW_MATCH(sk, net, hash, acookie,
> -					saddr, daddr, ports, dif))
> -			goto hit;
> +					saddr, daddr, ports, dif)) {
> +			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt))) {
> +				sk = NULL;
> +				goto out;
> +			}
> +			if (unlikely(!INET_TW_MATCH(sk, net, hash, acookie,
> +				 saddr, daddr, ports, dif))) {
> +				sock_put(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:
> -	read_unlock(lock);
> +	rcu_read_unlock();
>  	return sk;
> -hit:
> -	sock_hold(sk);
> -	goto out;
>  }
>  EXPORT_SYMBOL_GPL(__inet_lookup_established);
> 
> @@ -272,14 +302,14 @@ static int __inet_check_established(struct inet_timewait_death_row *death_row,
>  	struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
>  	rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
>  	struct sock *sk2;
> -	const struct hlist_node *node;
> +	const struct hlist_nulls_node *node;
>  	struct inet_timewait_sock *tw;
> 
>  	prefetch(head->chain.first);
>  	write_lock(lock);
> 
>  	/* Check TIME-WAIT sockets first. */
> -	sk_for_each(sk2, node, &head->twchain) {
> +	sk_nulls_for_each(sk2, node, &head->twchain) {
>  		tw = inet_twsk(sk2);
> 
>  		if (INET_TW_MATCH(sk2, net, hash, acookie,
> @@ -293,7 +323,7 @@ static int __inet_check_established(struct inet_timewait_death_row *death_row,
>  	tw = NULL;
> 
>  	/* And established part... */
> -	sk_for_each(sk2, node, &head->chain) {
> +	sk_nulls_for_each(sk2, node, &head->chain) {
>  		if (INET_MATCH(sk2, net, hash, acookie,
>  					saddr, daddr, ports, dif))
>  			goto not_unique;
> @@ -306,7 +336,7 @@ unique:
>  	inet->sport = htons(lport);
>  	sk->sk_hash = hash;
>  	WARN_ON(!sk_unhashed(sk));
> -	__sk_add_node(sk, &head->chain);
> +	__sk_nulls_add_node_rcu(sk, &head->chain);
>  	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
>  	write_unlock(lock);
> 
> @@ -338,7 +368,7 @@ static inline u32 inet_sk_port_offset(const struct sock *sk)
>  void __inet_hash_nolisten(struct sock *sk)
>  {
>  	struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
> -	struct hlist_head *list;
> +	struct hlist_nulls_head *list;
>  	rwlock_t *lock;
>  	struct inet_ehash_bucket *head;
> 
> @@ -350,7 +380,7 @@ void __inet_hash_nolisten(struct sock *sk)
>  	lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
> 
>  	write_lock(lock);
> -	__sk_add_node(sk, list);
> +	__sk_nulls_add_node_rcu(sk, list);
>  	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
>  	write_unlock(lock);
>  }
> @@ -400,13 +430,15 @@ void inet_unhash(struct sock *sk)
>  		local_bh_disable();
>  		inet_listen_wlock(hashinfo);
>  		lock = &hashinfo->lhash_lock;
> +		if (__sk_del_node_init(sk))
> +			sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
>  	} else {
>  		lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
>  		write_lock_bh(lock);
> +		if (__sk_nulls_del_node_init_rcu(sk))
> +			sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
>  	}
> 
> -	if (__sk_del_node_init(sk))
> -		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
>  	write_unlock_bh(lock);
>  out:
>  	if (sk->sk_state == TCP_LISTEN)
> diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
> index 1c5fd38..6068995 100644
> --- a/net/ipv4/inet_timewait_sock.c
> +++ b/net/ipv4/inet_timewait_sock.c
> @@ -23,12 +23,12 @@ static void __inet_twsk_kill(struct inet_timewait_sock *tw,
>  	rwlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
> 
>  	write_lock(lock);
> -	if (hlist_unhashed(&tw->tw_node)) {
> +	if (hlist_nulls_unhashed(&tw->tw_node)) {
>  		write_unlock(lock);
>  		return;
>  	}
> -	__hlist_del(&tw->tw_node);
> -	sk_node_init(&tw->tw_node);
> +	hlist_nulls_del_rcu(&tw->tw_node);
> +	sk_nulls_node_init(&tw->tw_node);
>  	write_unlock(lock);
> 
>  	/* Disassociate with bind bucket. */
> @@ -92,13 +92,17 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
> 
>  	write_lock(lock);
> 
> -	/* Step 2: Remove SK from established hash. */
> -	if (__sk_del_node_init(sk))
> -		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
> -
> -	/* Step 3: Hash TW into TIMEWAIT chain. */
> -	inet_twsk_add_node(tw, &ehead->twchain);
> +	/*
> +	 * Step 2: Hash TW into TIMEWAIT chain.
> +	 * Should be done before removing sk from established chain
> +	 * because readers are lockless and search established first.
> +	 */
>  	atomic_inc(&tw->tw_refcnt);
> +	inet_twsk_add_node_rcu(tw, &ehead->twchain);
> +
> +	/* Step 3: Remove SK from established hash. */
> +	if (__sk_nulls_del_node_init_rcu(sk))
> +		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
> 
>  	write_unlock(lock);
>  }
> @@ -416,7 +420,7 @@ void inet_twsk_purge(struct net *net, struct inet_hashinfo *hashinfo,
>  {
>  	struct inet_timewait_sock *tw;
>  	struct sock *sk;
> -	struct hlist_node *node;
> +	struct hlist_nulls_node *node;
>  	int h;
> 
>  	local_bh_disable();
> @@ -426,7 +430,7 @@ void inet_twsk_purge(struct net *net, struct inet_hashinfo *hashinfo,
>  		rwlock_t *lock = inet_ehash_lockp(hashinfo, h);
>  restart:
>  		write_lock(lock);
> -		sk_for_each(sk, node, &head->twchain) {
> +		sk_nulls_for_each(sk, node, &head->twchain) {
> 
>  			tw = inet_twsk(sk);
>  			if (!net_eq(twsk_net(tw), net) ||
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index f60a591..044224a 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2707,8 +2707,8 @@ void __init tcp_init(void)
>  					thash_entries ? 0 : 512 * 1024);
>  	tcp_hashinfo.ehash_size = 1 << tcp_hashinfo.ehash_size;
>  	for (i = 0; i < tcp_hashinfo.ehash_size; i++) {
> -		INIT_HLIST_HEAD(&tcp_hashinfo.ehash[i].chain);
> -		INIT_HLIST_HEAD(&tcp_hashinfo.ehash[i].twchain);
> +		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");
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index d49233f..b2e3ab2 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1857,16 +1857,16 @@ EXPORT_SYMBOL(tcp_v4_destroy_sock);
>  #ifdef CONFIG_PROC_FS
>  /* Proc filesystem TCP sock list dumping. */
> 
> -static inline struct inet_timewait_sock *tw_head(struct hlist_head *head)
> +static inline struct inet_timewait_sock *tw_head(struct hlist_nulls_head *head)
>  {
> -	return hlist_empty(head) ? NULL :
> +	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 tw->tw_node.next ?
> -		hlist_entry(tw->tw_node.next, typeof(*tw), tw_node) : NULL;
> +	return !is_a_nulls(tw->tw_node.next) ?
> +		hlist_nulls_entry(tw->tw_node.next, typeof(*tw), tw_node) : NULL;
>  }
> 
>  static void *listening_get_next(struct seq_file *seq, void *cur)
> @@ -1954,8 +1954,8 @@ static void *listening_get_idx(struct seq_file *seq, loff_t *pos)
> 
>  static inline int empty_bucket(struct tcp_iter_state *st)
>  {
> -	return hlist_empty(&tcp_hashinfo.ehash[st->bucket].chain) &&
> -		hlist_empty(&tcp_hashinfo.ehash[st->bucket].twchain);
> +	return hlist_nulls_empty(&tcp_hashinfo.ehash[st->bucket].chain) &&
> +		hlist_nulls_empty(&tcp_hashinfo.ehash[st->bucket].twchain);
>  }
> 
>  static void *established_get_first(struct seq_file *seq)
> @@ -1966,7 +1966,7 @@ static void *established_get_first(struct seq_file *seq)
> 
>  	for (st->bucket = 0; st->bucket < tcp_hashinfo.ehash_size; ++st->bucket) {
>  		struct sock *sk;
> -		struct hlist_node *node;
> +		struct hlist_nulls_node *node;
>  		struct inet_timewait_sock *tw;
>  		rwlock_t *lock = inet_ehash_lockp(&tcp_hashinfo, st->bucket);
> 
> @@ -1975,7 +1975,7 @@ static void *established_get_first(struct seq_file *seq)
>  			continue;
> 
>  		read_lock_bh(lock);
> -		sk_for_each(sk, node, &tcp_hashinfo.ehash[st->bucket].chain) {
> +		sk_nulls_for_each(sk, node, &tcp_hashinfo.ehash[st->bucket].chain) {
>  			if (sk->sk_family != st->family ||
>  			    !net_eq(sock_net(sk), net)) {
>  				continue;
> @@ -2004,7 +2004,7 @@ static void *established_get_next(struct seq_file *seq, void *cur)
>  {
>  	struct sock *sk = cur;
>  	struct inet_timewait_sock *tw;
> -	struct hlist_node *node;
> +	struct hlist_nulls_node *node;
>  	struct tcp_iter_state *st = seq->private;
>  	struct net *net = seq_file_net(seq);
> 
> @@ -2032,11 +2032,11 @@ get_tw:
>  			return NULL;
> 
>  		read_lock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
> -		sk = sk_head(&tcp_hashinfo.ehash[st->bucket].chain);
> +		sk = sk_nulls_head(&tcp_hashinfo.ehash[st->bucket].chain);
>  	} else
> -		sk = sk_next(sk);
> +		sk = sk_nulls_next(sk);
> 
> -	sk_for_each_from(sk, node) {
> +	sk_nulls_for_each_from(sk, node) {
>  		if (sk->sk_family == st->family && net_eq(sock_net(sk), net))
>  			goto found;
>  	}
> @@ -2375,6 +2375,7 @@ struct proto tcp_prot = {
>  	.sysctl_rmem		= sysctl_tcp_rmem,
>  	.max_header		= MAX_TCP_HEADER,
>  	.obj_size		= sizeof(struct tcp_sock),
> +	.slab_flags		= SLAB_DESTROY_BY_RCU,
>  	.twsk_prot		= &tcp_timewait_sock_ops,
>  	.rsk_prot		= &tcp_request_sock_ops,
>  	.h.hashinfo		= &tcp_hashinfo,
> diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
> index 1646a56..c1b4d40 100644
> --- a/net/ipv6/inet6_hashtables.c
> +++ b/net/ipv6/inet6_hashtables.c
> @@ -25,24 +25,28 @@
>  void __inet6_hash(struct sock *sk)
>  {
>  	struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
> -	struct hlist_head *list;
>  	rwlock_t *lock;
> 
>  	WARN_ON(!sk_unhashed(sk));
> 
>  	if (sk->sk_state == TCP_LISTEN) {
> +		struct hlist_head *list;
> +
>  		list = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
>  		lock = &hashinfo->lhash_lock;
>  		inet_listen_wlock(hashinfo);
> +		__sk_add_node(sk, list);
>  	} else {
>  		unsigned int hash;
> +		struct hlist_nulls_head *list;
> +
>  		sk->sk_hash = hash = inet6_sk_ehashfn(sk);
>  		list = &inet_ehash_bucket(hashinfo, hash)->chain;
>  		lock = inet_ehash_lockp(hashinfo, hash);
>  		write_lock(lock);
> +		__sk_nulls_add_node_rcu(sk, list);
>  	}
> 
> -	__sk_add_node(sk, list);
>  	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
>  	write_unlock(lock);
>  }
> @@ -63,33 +67,53 @@ struct sock *__inet6_lookup_established(struct net *net,
>  					   const int dif)
>  {
>  	struct sock *sk;
> -	const struct hlist_node *node;
> +	const struct hlist_nulls_node *node;
>  	const __portpair ports = INET_COMBINED_PORTS(sport, hnum);
>  	/* Optimize here for direct hit, only listening connections can
>  	 * have wildcards anyways.
>  	 */
>  	unsigned int hash = inet6_ehashfn(net, daddr, hnum, saddr, sport);
> -	struct inet_ehash_bucket *head = inet_ehash_bucket(hashinfo, hash);
> -	rwlock_t *lock = inet_ehash_lockp(hashinfo, hash);
> +	unsigned int slot = hash & (hashinfo->ehash_size - 1);
> +	struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
> 
> -	prefetch(head->chain.first);
> -	read_lock(lock);
> -	sk_for_each(sk, node, &head->chain) {
> +
> +	rcu_read_lock();
> +begin:
> +	sk_nulls_for_each_rcu(sk, node, &head->chain) {
>  		/* For IPV6 do the cheaper port and family tests first. */
> -		if (INET6_MATCH(sk, net, hash, saddr, daddr, ports, dif))
> -			goto hit; /* You sunk my battleship! */
> +		if (INET6_MATCH(sk, net, hash, saddr, daddr, ports, dif)) {
> +			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
> +				goto begintw;
> +			if (!INET6_MATCH(sk, net, hash, saddr, daddr, ports, dif)) {
> +				sock_put(sk);
> +				goto begin;
> +			}
> +		goto out;
> +		}
>  	}
> +	if (get_nulls_value(node) != slot)
> +		goto begin;
> +
> +begintw:
>  	/* Must check for a TIME_WAIT'er before going to listener hash. */
> -	sk_for_each(sk, node, &head->twchain) {
> -		if (INET6_TW_MATCH(sk, net, hash, saddr, daddr, ports, dif))
> -			goto hit;
> +	sk_nulls_for_each_rcu(sk, node, &head->twchain) {
> +		if (INET6_TW_MATCH(sk, net, hash, saddr, daddr, ports, dif)) {
> +			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt))) {
> +				sk = NULL;
> +				goto out;
> +			}
> +			if (!INET6_TW_MATCH(sk, net, hash, saddr, daddr, ports, dif)) {
> +				sock_put(sk);
> +				goto begintw;
> +			}
> +			goto out;
> +		}
>  	}
> -	read_unlock(lock);
> -	return NULL;
> -
> -hit:
> -	sock_hold(sk);
> -	read_unlock(lock);
> +	if (get_nulls_value(node) != slot)
> +		goto begintw;
> +	sk = NULL;
> +out:
> +	rcu_read_unlock();
>  	return sk;
>  }
>  EXPORT_SYMBOL(__inet6_lookup_established);
> @@ -172,14 +196,14 @@ static int __inet6_check_established(struct inet_timewait_death_row *death_row,
>  	struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
>  	rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
>  	struct sock *sk2;
> -	const struct hlist_node *node;
> +	const struct hlist_nulls_node *node;
>  	struct inet_timewait_sock *tw;
> 
>  	prefetch(head->chain.first);
>  	write_lock(lock);
> 
>  	/* Check TIME-WAIT sockets first. */
> -	sk_for_each(sk2, node, &head->twchain) {
> +	sk_nulls_for_each(sk2, node, &head->twchain) {
>  		tw = inet_twsk(sk2);
> 
>  		if (INET6_TW_MATCH(sk2, net, hash, saddr, daddr, ports, dif)) {
> @@ -192,7 +216,7 @@ static int __inet6_check_established(struct inet_timewait_death_row *death_row,
>  	tw = NULL;
> 
>  	/* And established part... */
> -	sk_for_each(sk2, node, &head->chain) {
> +	sk_nulls_for_each(sk2, node, &head->chain) {
>  		if (INET6_MATCH(sk2, net, hash, saddr, daddr, ports, dif))
>  			goto not_unique;
>  	}
> @@ -203,7 +227,7 @@ unique:
>  	inet->num = lport;
>  	inet->sport = htons(lport);
>  	WARN_ON(!sk_unhashed(sk));
> -	__sk_add_node(sk, &head->chain);
> +	__sk_nulls_add_node_rcu(sk, &head->chain);
>  	sk->sk_hash = hash;
>  	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
>  	write_unlock(lock);
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 9842764..b357870 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -2043,6 +2043,7 @@ struct proto tcpv6_prot = {
>  	.sysctl_rmem		= sysctl_tcp_rmem,
>  	.max_header		= MAX_TCP_HEADER,
>  	.obj_size		= sizeof(struct tcp6_sock),
> +	.slab_flags		= SLAB_DESTROY_BY_RCU,
>  	.twsk_prot		= &tcp6_timewait_sock_ops,
>  	.rsk_prot		= &tcp6_request_sock_ops,
>  	.h.hashinfo		= &tcp_hashinfo,

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Patch

diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
index cb31fbf..4818960 100644
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -41,8 +41,8 @@ 
  * I'll experiment with dynamic table growth later.
  */
 struct inet_ehash_bucket {
-	struct hlist_head chain;
-	struct hlist_head twchain;
+	struct hlist_nulls_head chain;
+	struct hlist_nulls_head twchain;
 };
 
 /* There are a few simple rules, which allow for local port reuse by
diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h
index 80e4977..4b8ece2 100644
--- a/include/net/inet_timewait_sock.h
+++ b/include/net/inet_timewait_sock.h
@@ -110,7 +110,7 @@  struct inet_timewait_sock {
 #define tw_state		__tw_common.skc_state
 #define tw_reuse		__tw_common.skc_reuse
 #define tw_bound_dev_if		__tw_common.skc_bound_dev_if
-#define tw_node			__tw_common.skc_node
+#define tw_node			__tw_common.skc_nulls_node
 #define tw_bind_node		__tw_common.skc_bind_node
 #define tw_refcnt		__tw_common.skc_refcnt
 #define tw_hash			__tw_common.skc_hash
@@ -137,10 +137,10 @@  struct inet_timewait_sock {
 	struct hlist_node	tw_death_node;
 };
 
-static inline void inet_twsk_add_node(struct inet_timewait_sock *tw,
-				      struct hlist_head *list)
+static inline void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
+				      struct hlist_nulls_head *list)
 {
-	hlist_add_head(&tw->tw_node, list);
+	hlist_nulls_add_head_rcu(&tw->tw_node, list);
 }
 
 static inline void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
@@ -175,7 +175,7 @@  static inline int inet_twsk_del_dead_node(struct inet_timewait_sock *tw)
 }
 
 #define inet_twsk_for_each(tw, node, head) \
-	hlist_for_each_entry(tw, node, head, tw_node)
+	hlist_nulls_for_each_entry(tw, node, head, tw_node)
 
 #define inet_twsk_for_each_inmate(tw, node, jail) \
 	hlist_for_each_entry(tw, node, jail, tw_death_node)
diff --git a/net/core/sock.c b/net/core/sock.c
index ded1eb5..38de9c3 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2082,7 +2082,9 @@  int proto_register(struct proto *prot, int alloc_slab)
 			prot->twsk_prot->twsk_slab =
 				kmem_cache_create(timewait_sock_slab_name,
 						  prot->twsk_prot->twsk_obj_size,
-						  0, SLAB_HWCACHE_ALIGN,
+						  0,
+						  SLAB_HWCACHE_ALIGN |
+							prot->slab_flags,
 						  NULL);
 			if (prot->twsk_prot->twsk_slab == NULL)
 				goto out_free_timewait_sock_slab_name;
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 528baa2..d1dd952 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -938,6 +938,7 @@  static struct proto dccp_v4_prot = {
 	.orphan_count		= &dccp_orphan_count,
 	.max_header		= MAX_DCCP_HEADER,
 	.obj_size		= sizeof(struct dccp_sock),
+	.slab_flags		= SLAB_DESTROY_BY_RCU,
 	.rsk_prot		= &dccp_request_sock_ops,
 	.twsk_prot		= &dccp_timewait_sock_ops,
 	.h.hashinfo		= &dccp_hashinfo,
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 4aa1148..f033e84 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -1140,6 +1140,7 @@  static struct proto dccp_v6_prot = {
 	.orphan_count	   = &dccp_orphan_count,
 	.max_header	   = MAX_DCCP_HEADER,
 	.obj_size	   = sizeof(struct dccp6_sock),
+	.slab_flags	   = SLAB_DESTROY_BY_RCU,
 	.rsk_prot	   = &dccp6_request_sock_ops,
 	.twsk_prot	   = &dccp6_timewait_sock_ops,
 	.h.hashinfo	   = &dccp_hashinfo,
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 46cb349..1117d4d 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -1090,8 +1090,8 @@  static int __init dccp_init(void)
 	}
 
 	for (i = 0; i < dccp_hashinfo.ehash_size; i++) {
-		INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].chain);
-		INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].twchain);
+		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))
diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 564230d..41b3672 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -778,18 +778,19 @@  skip_listen_ht:
 		struct inet_ehash_bucket *head = &hashinfo->ehash[i];
 		rwlock_t *lock = inet_ehash_lockp(hashinfo, i);
 		struct sock *sk;
-		struct hlist_node *node;
+		struct hlist_nulls_node *node;
 
 		num = 0;
 
-		if (hlist_empty(&head->chain) && hlist_empty(&head->twchain))
+		if (hlist_nulls_empty(&head->chain) &&
+			hlist_nulls_empty(&head->twchain))
 			continue;
 
 		if (i > s_i)
 			s_num = 0;
 
 		read_lock_bh(lock);
-		sk_for_each(sk, node, &head->chain) {
+		sk_nulls_for_each(sk, node, &head->chain) {
 			struct inet_sock *inet = inet_sk(sk);
 
 			if (num < s_num)
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index be41ebb..fd269cf 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -223,35 +223,65 @@  struct sock * __inet_lookup_established(struct net *net,
 	INET_ADDR_COOKIE(acookie, saddr, daddr)
 	const __portpair ports = INET_COMBINED_PORTS(sport, hnum);
 	struct sock *sk;
-	const struct hlist_node *node;
+	const struct hlist_nulls_node *node;
 	/* Optimize here for direct hit, only listening connections can
 	 * have wildcards anyways.
 	 */
 	unsigned int hash = inet_ehashfn(net, daddr, hnum, saddr, sport);
-	struct inet_ehash_bucket *head = inet_ehash_bucket(hashinfo, hash);
-	rwlock_t *lock = inet_ehash_lockp(hashinfo, hash);
+	unsigned int slot = hash & (hashinfo->ehash_size - 1);
+	struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
 
-	prefetch(head->chain.first);
-	read_lock(lock);
-	sk_for_each(sk, node, &head->chain) {
+	rcu_read_lock();
+begin:
+	sk_nulls_for_each_rcu(sk, node, &head->chain) {
 		if (INET_MATCH(sk, net, hash, acookie,
-					saddr, daddr, ports, dif))
-			goto hit; /* You sunk my battleship! */
+					saddr, daddr, ports, dif)) {
+			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
+				goto begintw;
+			if (unlikely(!INET_MATCH(sk, net, hash, acookie,
+				saddr, daddr, ports, dif))) {
+				sock_put(sk);
+				goto begin;
+			}
+			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 begin;
 
+begintw:
 	/* Must check for a TIME_WAIT'er before going to listener hash. */
-	sk_for_each(sk, node, &head->twchain) {
+	sk_nulls_for_each_rcu(sk, node, &head->twchain) {
 		if (INET_TW_MATCH(sk, net, hash, acookie,
-					saddr, daddr, ports, dif))
-			goto hit;
+					saddr, daddr, ports, dif)) {
+			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt))) {
+				sk = NULL;
+				goto out;
+			}
+			if (unlikely(!INET_TW_MATCH(sk, net, hash, acookie,
+				 saddr, daddr, ports, dif))) {
+				sock_put(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:
-	read_unlock(lock);
+	rcu_read_unlock();
 	return sk;
-hit:
-	sock_hold(sk);
-	goto out;
 }
 EXPORT_SYMBOL_GPL(__inet_lookup_established);
 
@@ -272,14 +302,14 @@  static int __inet_check_established(struct inet_timewait_death_row *death_row,
 	struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
 	rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
 	struct sock *sk2;
-	const struct hlist_node *node;
+	const struct hlist_nulls_node *node;
 	struct inet_timewait_sock *tw;
 
 	prefetch(head->chain.first);
 	write_lock(lock);
 
 	/* Check TIME-WAIT sockets first. */
-	sk_for_each(sk2, node, &head->twchain) {
+	sk_nulls_for_each(sk2, node, &head->twchain) {
 		tw = inet_twsk(sk2);
 
 		if (INET_TW_MATCH(sk2, net, hash, acookie,
@@ -293,7 +323,7 @@  static int __inet_check_established(struct inet_timewait_death_row *death_row,
 	tw = NULL;
 
 	/* And established part... */
-	sk_for_each(sk2, node, &head->chain) {
+	sk_nulls_for_each(sk2, node, &head->chain) {
 		if (INET_MATCH(sk2, net, hash, acookie,
 					saddr, daddr, ports, dif))
 			goto not_unique;
@@ -306,7 +336,7 @@  unique:
 	inet->sport = htons(lport);
 	sk->sk_hash = hash;
 	WARN_ON(!sk_unhashed(sk));
-	__sk_add_node(sk, &head->chain);
+	__sk_nulls_add_node_rcu(sk, &head->chain);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 	write_unlock(lock);
 
@@ -338,7 +368,7 @@  static inline u32 inet_sk_port_offset(const struct sock *sk)
 void __inet_hash_nolisten(struct sock *sk)
 {
 	struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
-	struct hlist_head *list;
+	struct hlist_nulls_head *list;
 	rwlock_t *lock;
 	struct inet_ehash_bucket *head;
 
@@ -350,7 +380,7 @@  void __inet_hash_nolisten(struct sock *sk)
 	lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 
 	write_lock(lock);
-	__sk_add_node(sk, list);
+	__sk_nulls_add_node_rcu(sk, list);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 	write_unlock(lock);
 }
@@ -400,13 +430,15 @@  void inet_unhash(struct sock *sk)
 		local_bh_disable();
 		inet_listen_wlock(hashinfo);
 		lock = &hashinfo->lhash_lock;
+		if (__sk_del_node_init(sk))
+			sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 	} else {
 		lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 		write_lock_bh(lock);
+		if (__sk_nulls_del_node_init_rcu(sk))
+			sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 	}
 
-	if (__sk_del_node_init(sk))
-		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 	write_unlock_bh(lock);
 out:
 	if (sk->sk_state == TCP_LISTEN)
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 1c5fd38..6068995 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -23,12 +23,12 @@  static void __inet_twsk_kill(struct inet_timewait_sock *tw,
 	rwlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
 
 	write_lock(lock);
-	if (hlist_unhashed(&tw->tw_node)) {
+	if (hlist_nulls_unhashed(&tw->tw_node)) {
 		write_unlock(lock);
 		return;
 	}
-	__hlist_del(&tw->tw_node);
-	sk_node_init(&tw->tw_node);
+	hlist_nulls_del_rcu(&tw->tw_node);
+	sk_nulls_node_init(&tw->tw_node);
 	write_unlock(lock);
 
 	/* Disassociate with bind bucket. */
@@ -92,13 +92,17 @@  void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
 
 	write_lock(lock);
 
-	/* Step 2: Remove SK from established hash. */
-	if (__sk_del_node_init(sk))
-		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
-
-	/* Step 3: Hash TW into TIMEWAIT chain. */
-	inet_twsk_add_node(tw, &ehead->twchain);
+	/*
+	 * Step 2: Hash TW into TIMEWAIT chain.
+	 * Should be done before removing sk from established chain
+	 * because readers are lockless and search established first.
+	 */
 	atomic_inc(&tw->tw_refcnt);
+	inet_twsk_add_node_rcu(tw, &ehead->twchain);
+
+	/* Step 3: Remove SK from established hash. */
+	if (__sk_nulls_del_node_init_rcu(sk))
+		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 
 	write_unlock(lock);
 }
@@ -416,7 +420,7 @@  void inet_twsk_purge(struct net *net, struct inet_hashinfo *hashinfo,
 {
 	struct inet_timewait_sock *tw;
 	struct sock *sk;
-	struct hlist_node *node;
+	struct hlist_nulls_node *node;
 	int h;
 
 	local_bh_disable();
@@ -426,7 +430,7 @@  void inet_twsk_purge(struct net *net, struct inet_hashinfo *hashinfo,
 		rwlock_t *lock = inet_ehash_lockp(hashinfo, h);
 restart:
 		write_lock(lock);
-		sk_for_each(sk, node, &head->twchain) {
+		sk_nulls_for_each(sk, node, &head->twchain) {
 
 			tw = inet_twsk(sk);
 			if (!net_eq(twsk_net(tw), net) ||
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f60a591..044224a 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2707,8 +2707,8 @@  void __init tcp_init(void)
 					thash_entries ? 0 : 512 * 1024);
 	tcp_hashinfo.ehash_size = 1 << tcp_hashinfo.ehash_size;
 	for (i = 0; i < tcp_hashinfo.ehash_size; i++) {
-		INIT_HLIST_HEAD(&tcp_hashinfo.ehash[i].chain);
-		INIT_HLIST_HEAD(&tcp_hashinfo.ehash[i].twchain);
+		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");
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index d49233f..b2e3ab2 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1857,16 +1857,16 @@  EXPORT_SYMBOL(tcp_v4_destroy_sock);
 #ifdef CONFIG_PROC_FS
 /* Proc filesystem TCP sock list dumping. */
 
-static inline struct inet_timewait_sock *tw_head(struct hlist_head *head)
+static inline struct inet_timewait_sock *tw_head(struct hlist_nulls_head *head)
 {
-	return hlist_empty(head) ? NULL :
+	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 tw->tw_node.next ?
-		hlist_entry(tw->tw_node.next, typeof(*tw), tw_node) : NULL;
+	return !is_a_nulls(tw->tw_node.next) ?
+		hlist_nulls_entry(tw->tw_node.next, typeof(*tw), tw_node) : NULL;
 }
 
 static void *listening_get_next(struct seq_file *seq, void *cur)
@@ -1954,8 +1954,8 @@  static void *listening_get_idx(struct seq_file *seq, loff_t *pos)
 
 static inline int empty_bucket(struct tcp_iter_state *st)
 {
-	return hlist_empty(&tcp_hashinfo.ehash[st->bucket].chain) &&
-		hlist_empty(&tcp_hashinfo.ehash[st->bucket].twchain);
+	return hlist_nulls_empty(&tcp_hashinfo.ehash[st->bucket].chain) &&
+		hlist_nulls_empty(&tcp_hashinfo.ehash[st->bucket].twchain);
 }
 
 static void *established_get_first(struct seq_file *seq)
@@ -1966,7 +1966,7 @@  static void *established_get_first(struct seq_file *seq)
 
 	for (st->bucket = 0; st->bucket < tcp_hashinfo.ehash_size; ++st->bucket) {
 		struct sock *sk;
-		struct hlist_node *node;
+		struct hlist_nulls_node *node;
 		struct inet_timewait_sock *tw;
 		rwlock_t *lock = inet_ehash_lockp(&tcp_hashinfo, st->bucket);
 
@@ -1975,7 +1975,7 @@  static void *established_get_first(struct seq_file *seq)
 			continue;
 
 		read_lock_bh(lock);
-		sk_for_each(sk, node, &tcp_hashinfo.ehash[st->bucket].chain) {
+		sk_nulls_for_each(sk, node, &tcp_hashinfo.ehash[st->bucket].chain) {
 			if (sk->sk_family != st->family ||
 			    !net_eq(sock_net(sk), net)) {
 				continue;
@@ -2004,7 +2004,7 @@  static void *established_get_next(struct seq_file *seq, void *cur)
 {
 	struct sock *sk = cur;
 	struct inet_timewait_sock *tw;
-	struct hlist_node *node;
+	struct hlist_nulls_node *node;
 	struct tcp_iter_state *st = seq->private;
 	struct net *net = seq_file_net(seq);
 
@@ -2032,11 +2032,11 @@  get_tw:
 			return NULL;
 
 		read_lock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
-		sk = sk_head(&tcp_hashinfo.ehash[st->bucket].chain);
+		sk = sk_nulls_head(&tcp_hashinfo.ehash[st->bucket].chain);
 	} else
-		sk = sk_next(sk);
+		sk = sk_nulls_next(sk);
 
-	sk_for_each_from(sk, node) {
+	sk_nulls_for_each_from(sk, node) {
 		if (sk->sk_family == st->family && net_eq(sock_net(sk), net))
 			goto found;
 	}
@@ -2375,6 +2375,7 @@  struct proto tcp_prot = {
 	.sysctl_rmem		= sysctl_tcp_rmem,
 	.max_header		= MAX_TCP_HEADER,
 	.obj_size		= sizeof(struct tcp_sock),
+	.slab_flags		= SLAB_DESTROY_BY_RCU,
 	.twsk_prot		= &tcp_timewait_sock_ops,
 	.rsk_prot		= &tcp_request_sock_ops,
 	.h.hashinfo		= &tcp_hashinfo,
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index 1646a56..c1b4d40 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -25,24 +25,28 @@ 
 void __inet6_hash(struct sock *sk)
 {
 	struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
-	struct hlist_head *list;
 	rwlock_t *lock;
 
 	WARN_ON(!sk_unhashed(sk));
 
 	if (sk->sk_state == TCP_LISTEN) {
+		struct hlist_head *list;
+
 		list = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
 		lock = &hashinfo->lhash_lock;
 		inet_listen_wlock(hashinfo);
+		__sk_add_node(sk, list);
 	} else {
 		unsigned int hash;
+		struct hlist_nulls_head *list;
+
 		sk->sk_hash = hash = inet6_sk_ehashfn(sk);
 		list = &inet_ehash_bucket(hashinfo, hash)->chain;
 		lock = inet_ehash_lockp(hashinfo, hash);
 		write_lock(lock);
+		__sk_nulls_add_node_rcu(sk, list);
 	}
 
-	__sk_add_node(sk, list);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 	write_unlock(lock);
 }
@@ -63,33 +67,53 @@  struct sock *__inet6_lookup_established(struct net *net,
 					   const int dif)
 {
 	struct sock *sk;
-	const struct hlist_node *node;
+	const struct hlist_nulls_node *node;
 	const __portpair ports = INET_COMBINED_PORTS(sport, hnum);
 	/* Optimize here for direct hit, only listening connections can
 	 * have wildcards anyways.
 	 */
 	unsigned int hash = inet6_ehashfn(net, daddr, hnum, saddr, sport);
-	struct inet_ehash_bucket *head = inet_ehash_bucket(hashinfo, hash);
-	rwlock_t *lock = inet_ehash_lockp(hashinfo, hash);
+	unsigned int slot = hash & (hashinfo->ehash_size - 1);
+	struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
 
-	prefetch(head->chain.first);
-	read_lock(lock);
-	sk_for_each(sk, node, &head->chain) {
+
+	rcu_read_lock();
+begin:
+	sk_nulls_for_each_rcu(sk, node, &head->chain) {
 		/* For IPV6 do the cheaper port and family tests first. */
-		if (INET6_MATCH(sk, net, hash, saddr, daddr, ports, dif))
-			goto hit; /* You sunk my battleship! */
+		if (INET6_MATCH(sk, net, hash, saddr, daddr, ports, dif)) {
+			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
+				goto begintw;
+			if (!INET6_MATCH(sk, net, hash, saddr, daddr, ports, dif)) {
+				sock_put(sk);
+				goto begin;
+			}
+		goto out;
+		}
 	}
+	if (get_nulls_value(node) != slot)
+		goto begin;
+
+begintw:
 	/* Must check for a TIME_WAIT'er before going to listener hash. */
-	sk_for_each(sk, node, &head->twchain) {
-		if (INET6_TW_MATCH(sk, net, hash, saddr, daddr, ports, dif))
-			goto hit;
+	sk_nulls_for_each_rcu(sk, node, &head->twchain) {
+		if (INET6_TW_MATCH(sk, net, hash, saddr, daddr, ports, dif)) {
+			if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt))) {
+				sk = NULL;
+				goto out;
+			}
+			if (!INET6_TW_MATCH(sk, net, hash, saddr, daddr, ports, dif)) {
+				sock_put(sk);
+				goto begintw;
+			}
+			goto out;
+		}
 	}
-	read_unlock(lock);
-	return NULL;
-
-hit:
-	sock_hold(sk);
-	read_unlock(lock);
+	if (get_nulls_value(node) != slot)
+		goto begintw;
+	sk = NULL;
+out:
+	rcu_read_unlock();
 	return sk;
 }
 EXPORT_SYMBOL(__inet6_lookup_established);
@@ -172,14 +196,14 @@  static int __inet6_check_established(struct inet_timewait_death_row *death_row,
 	struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
 	rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
 	struct sock *sk2;
-	const struct hlist_node *node;
+	const struct hlist_nulls_node *node;
 	struct inet_timewait_sock *tw;
 
 	prefetch(head->chain.first);
 	write_lock(lock);
 
 	/* Check TIME-WAIT sockets first. */
-	sk_for_each(sk2, node, &head->twchain) {
+	sk_nulls_for_each(sk2, node, &head->twchain) {
 		tw = inet_twsk(sk2);
 
 		if (INET6_TW_MATCH(sk2, net, hash, saddr, daddr, ports, dif)) {
@@ -192,7 +216,7 @@  static int __inet6_check_established(struct inet_timewait_death_row *death_row,
 	tw = NULL;
 
 	/* And established part... */
-	sk_for_each(sk2, node, &head->chain) {
+	sk_nulls_for_each(sk2, node, &head->chain) {
 		if (INET6_MATCH(sk2, net, hash, saddr, daddr, ports, dif))
 			goto not_unique;
 	}
@@ -203,7 +227,7 @@  unique:
 	inet->num = lport;
 	inet->sport = htons(lport);
 	WARN_ON(!sk_unhashed(sk));
-	__sk_add_node(sk, &head->chain);
+	__sk_nulls_add_node_rcu(sk, &head->chain);
 	sk->sk_hash = hash;
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 	write_unlock(lock);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 9842764..b357870 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -2043,6 +2043,7 @@  struct proto tcpv6_prot = {
 	.sysctl_rmem		= sysctl_tcp_rmem,
 	.max_header		= MAX_TCP_HEADER,
 	.obj_size		= sizeof(struct tcp6_sock),
+	.slab_flags		= SLAB_DESTROY_BY_RCU,
 	.twsk_prot		= &tcp6_timewait_sock_ops,
 	.rsk_prot		= &tcp6_request_sock_ops,
 	.h.hashinfo		= &tcp_hashinfo,