Subject: Re: [PATCH] netfilter: use per-cpu recursive spinlock (v6)

From: "Paul E. McKenney" <[email-masked]>
Date: Thu, 16 Apr 2009 10:58:50 -0700

On Thu, Apr 16, 2009 at 06:10:30PM +0200, Eric Dumazet wrote:
> Paul E. McKenney a écrit :
> 
> > Well, we don't really need an rwlock, especially given that we really
> > don't want two "readers" incrementing the same counter concurrently.
> > 
> > A safer approach would be to maintain a flag in the task structure
> > tracking which (if any) of the per-CPU locks you hold.  Also maintain
> > a recursion-depth counter.  If the flag says you don't already hold
> > the lock, set it and acquire the lock.  Either way, increment the
> > recursion-depth counter:
> > 
> > 	if (current->netfilter_lock_held != cur_cpu) {
> > 		BUG_ON(current->netfilter_lock_held != CPU_NONE);
> > 		spin_lock(per_cpu(..., cur_cpu));
> > 		current->netfilter_lock_held = cur_cpu;
> > 	}
> > 	current->netfilter_lock_nesting++;
> > 
> > And reverse the process to unlock:
> > 
> > 	if (--current->netfilter_lock_nesting == 0) {
> > 		spin_unlock(per_cpu(..., cur_cpu));
> > 		current->netfilter_lock_held = CPU_NONE;
> > 	}
> > 
> 
> Yes, you are right, we can avoid rwlock, but use a 'recursive' lock
> or spin_trylock()
> 
> We can use one counter close to the spinlock, 
> no need to add one or two fields to every "thread_info"
> 
> struct rec_lock {
> 	spinlock_t lock;
> 	int        count;
> };
> static DEFINE_PER_CPU(struct rec_lock, ip_tables_lock);

Yep, much better approach!

> I also considered using regular spinlocks and spin_trylock() to "detect"
> the recurse case without a global counter.
> 
> lock :
> local_bh_disable();
> int locked = spin_trylock(&__get_cpu_var(arp_tables_lock);

Hmmm...

What happens if some other CPU is actually holding the lock?  For
example, the updater?

> unlock:
> 
> if (likely(locked))
> 	spin_unlock(&__get_cpu_var(arp_tables_lock));
> local_bh_enable();
> 
> But we would lose some runtime features, I dont feel comfortable about
> this trylock version. What others people think ?

I do not believe that it actually works.

I much prefer your earlier idea of associating a counter with the lock.

But an owner field is also required, please see below.  Or please let me
know what I am missing.

							Thanx, Paul

> Here is the resulting patch, based on Stephen v4
> 
> (Not sure we *need* recursive spinlock for the arp_tables, but it seems
> better to have an uniform implementation)
> 
> 
> [PATCH] netfilter: use per-cpu recursive spinlock (v6)
> 
> Yet another alternative version of ip/ip6/arp tables locking using
> per-cpu locks.  This avoids the overhead of synchronize_net() during
> update but still removes the expensive rwlock in earlier versions.
> 
> The idea for this came from an earlier version done by Eric Dumazet.
> Locking is done per-cpu, the fast path locks on the current cpu
> and updates counters.  The slow case involves acquiring the locks on
> all cpu's.
> 
> The mutex that was added for 2.6.30 in xt_table is unnecessary since
> there already is a mutex for xt[af].mutex that is held.
> 
> We have to use recursive spinlocks because netfilter can sometimes
> nest several calls to ipt_do_table() for a given cpu.
> 
> Signed-off-by: Stephen Hemminger <[email-masked]
> Signed-off-by: Eric Dumazet <[email-masked]>
> ---
>  include/linux/netfilter/x_tables.h |    5 -
>  net/ipv4/netfilter/arp_tables.c    |  131 +++++++++------------------
>  net/ipv4/netfilter/ip_tables.c     |  130 +++++++++-----------------
>  net/ipv6/netfilter/ip6_tables.c    |  127 +++++++++-----------------
>  net/netfilter/x_tables.c           |   26 -----
>  5 files changed, 138 insertions(+), 281 deletions(-)
> 
> diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
> index 7b1a652..1ff1a76 100644
> --- a/include/linux/netfilter/x_tables.h
> +++ b/include/linux/netfilter/x_tables.h
> @@ -354,9 +354,6 @@ struct xt_table
>  	/* What hooks you will enter on */
>  	unsigned int valid_hooks;
>  
> -	/* Lock for the curtain */
> -	struct mutex lock;
> -
>  	/* Man behind the curtain... */
>  	struct xt_table_info *private;
>  
> @@ -434,8 +431,6 @@ extern void xt_proto_fini(struct net *net, u_int8_t af);
>  
>  extern struct xt_table_info *xt_alloc_table_info(unsigned int size);
>  extern void xt_free_table_info(struct xt_table_info *info);
> -extern void xt_table_entry_swap_rcu(struct xt_table_info *old,
> -				    struct xt_table_info *new);
>  
>  /*
>   * This helper is performance critical and must be inlined
> diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
> index 5ba533d..9f935f2 100644
> --- a/net/ipv4/netfilter/arp_tables.c
> +++ b/net/ipv4/netfilter/arp_tables.c
> @@ -231,6 +231,12 @@ static inline struct arpt_entry *get_entry(void *base, unsigned int offset)
>  	return (struct arpt_entry *)(base + offset);
>  }
>  
> +struct rec_lock {
> +	spinlock_t lock;
> +	int	   count; /* recursion count */

We also need an owner field:

	int owner;

> +};
> +static DEFINE_PER_CPU(struct rec_lock, arp_tables_lock);
> +
>  unsigned int arpt_do_table(struct sk_buff *skb,
>  			   unsigned int hook,
>  			   const struct net_device *in,
> @@ -246,6 +252,7 @@ unsigned int arpt_do_table(struct sk_buff *skb,
>  	void *table_base;
>  	const struct xt_table_info *private;
>  	struct xt_target_param tgpar;
> +	struct rec_lock *rl;
>  
>  	if (!pskb_may_pull(skb, arp_hdr_len(skb->dev)))
>  		return NF_DROP;
> @@ -255,7 +262,12 @@ unsigned int arpt_do_table(struct sk_buff *skb,
>  
>  	rcu_read_lock_bh();
>  	private = rcu_dereference(table->private);
> -	table_base = rcu_dereference(private->entries[smp_processor_id()]);
> +
> +	rl = &__get_cpu_var(arp_tables_lock);
> +	if (likely(rl->count++ == 0))
> +		spin_lock(&rl->lock);

But if some other CPU holds the lock, this code would fail to wait for
that other CPU to release the lock, right?  It also might corrupt the
rl->count field due to two CPUs accessing it concurrently non-atomically.

I suggest the following, preferably in a function or macro or something:

	cur_cpu = smp_processor_id();
	if (likely(rl->owner != cur_cpu) {
		spin_lock(&rl->lock);
		rl->owner = smp_processor_id();
		rl->count = 1;
	} else {
		rl->count++;
	}

And the inverse for unlock.

Or am I missing something subtle?

> +
> +	table_base = private->entries[smp_processor_id()];
>  
>  	e = get_entry(table_base, private->hook_entry[hook]);
>  	back = get_entry(table_base, private->underflow[hook]);
> @@ -273,6 +285,7 @@ unsigned int arpt_do_table(struct sk_buff *skb,
>  
>  			hdr_len = sizeof(*arp) + (2 * sizeof(struct in_addr)) +
>  				(2 * skb->dev->addr_len);
> +
>  			ADD_COUNTER(e->counters, hdr_len, 1);
>  
>  			t = arpt_get_target(e);
> @@ -328,7 +341,8 @@ unsigned int arpt_do_table(struct sk_buff *skb,
>  			e = (void *)e + e->next_offset;
>  		}
>  	} while (!hotdrop);
> -
> +	if (likely(--rl->count == 0))
> +		spin_unlock(&rl->lock);
>  	rcu_read_unlock_bh();
>  
>  	if (hotdrop)
> @@ -716,74 +730,25 @@ static void get_counters(const struct xt_table_info *t,
>  	curcpu = raw_smp_processor_id();
>  
>  	i = 0;
> +	spin_lock_bh(&per_cpu(arp_tables_lock, curcpu).lock);
>  	ARPT_ENTRY_ITERATE(t->entries[curcpu],
>  			   t->size,
>  			   set_entry_to_counter,
>  			   counters,
>  			   &i);
> +	spin_unlock_bh(&per_cpu(arp_tables_lock, curcpu).lock);
>  
>  	for_each_possible_cpu(cpu) {
>  		if (cpu == curcpu)
>  			continue;
>  		i = 0;
> +		spin_lock_bh(&per_cpu(arp_tables_lock, cpu).lock);
>  		ARPT_ENTRY_ITERATE(t->entries[cpu],
>  				   t->size,
>  				   add_entry_to_counter,
>  				   counters,
>  				   &i);
> -	}
> -}
> -
> -
> -/* We're lazy, and add to the first CPU; overflow works its fey magic
> - * and everything is OK. */
> -static int
> -add_counter_to_entry(struct arpt_entry *e,
> -		     const struct xt_counters addme[],
> -		     unsigned int *i)
> -{
> -	ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
> -
> -	(*i)++;
> -	return 0;
> -}
> -
> -/* Take values from counters and add them back onto the current cpu */
> -static void put_counters(struct xt_table_info *t,
> -			 const struct xt_counters counters[])
> -{
> -	unsigned int i, cpu;
> -
> -	local_bh_disable();
> -	cpu = smp_processor_id();
> -	i = 0;
> -	ARPT_ENTRY_ITERATE(t->entries[cpu],
> -			  t->size,
> -			  add_counter_to_entry,
> -			  counters,
> -			  &i);
> -	local_bh_enable();
> -}
> -
> -static inline int
> -zero_entry_counter(struct arpt_entry *e, void *arg)
> -{
> -	e->counters.bcnt = 0;
> -	e->counters.pcnt = 0;
> -	return 0;
> -}
> -
> -static void
> -clone_counters(struct xt_table_info *newinfo, const struct xt_table_info *info)
> -{
> -	unsigned int cpu;
> -	const void *loc_cpu_entry = info->entries[raw_smp_processor_id()];
> -
> -	memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
> -	for_each_possible_cpu(cpu) {
> -		memcpy(newinfo->entries[cpu], loc_cpu_entry, info->size);
> -		ARPT_ENTRY_ITERATE(newinfo->entries[cpu], newinfo->size,
> -				  zero_entry_counter, NULL);
> +		spin_unlock_bh(&per_cpu(arp_tables_lock, cpu).lock);
>  	}
>  }
>  
> @@ -792,7 +757,6 @@ static struct xt_counters *alloc_counters(struct xt_table *table)
>  	unsigned int countersize;
>  	struct xt_counters *counters;
>  	struct xt_table_info *private = table->private;
> -	struct xt_table_info *info;
>  
>  	/* We need atomic snapshot of counters: rest doesn't change
>  	 * (other than comefrom, which userspace doesn't care
> @@ -802,30 +766,11 @@ static struct xt_counters *alloc_counters(struct xt_table *table)
>  	counters = vmalloc_node(countersize, numa_node_id());
>  
>  	if (counters == NULL)
> -		goto nomem;
> -
> -	info = xt_alloc_table_info(private->size);
> -	if (!info)
> -		goto free_counters;
> -
> -	clone_counters(info, private);
> +		return ERR_PTR(-ENOMEM);
>  
> -	mutex_lock(&table->lock);
> -	xt_table_entry_swap_rcu(private, info);
> -	synchronize_net();	/* Wait until smoke has cleared */
> -
> -	get_counters(info, counters);
> -	put_counters(private, counters);
> -	mutex_unlock(&table->lock);
> -
> -	xt_free_table_info(info);
> +	get_counters(private, counters);
>  
>  	return counters;
> -
> - free_counters:
> -	vfree(counters);
> - nomem:
> -	return ERR_PTR(-ENOMEM);
>  }
>  
>  static int copy_entries_to_user(unsigned int total_size,
> @@ -1165,6 +1110,19 @@ static int do_replace(struct net *net, void __user *user, unsigned int len)
>  	return ret;
>  }
>  
> +/* We're lazy, and add to the first CPU; overflow works its fey magic
> + * and everything is OK. */
> +static int
> +add_counter_to_entry(struct arpt_entry *e,
> +		     const struct xt_counters addme[],
> +		     unsigned int *i)
> +{
> +	ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
> +
> +	(*i)++;
> +	return 0;
> +}
> +
>  static int do_add_counters(struct net *net, void __user *user, unsigned int len,
>  			   int compat)
>  {
> @@ -1173,7 +1131,7 @@ static int do_add_counters(struct net *net, void __user *user, unsigned int len,
>  	struct xt_counters *paddc;
>  	unsigned int num_counters;
>  	const char *name;
> -	int size;
> +	int cpu, size;
>  	void *ptmp;
>  	struct xt_table *t;
>  	const struct xt_table_info *private;
> @@ -1224,25 +1182,25 @@ static int do_add_counters(struct net *net, void __user *user, unsigned int len,
>  		goto free;
>  	}
>  
> -	mutex_lock(&t->lock);
>  	private = t->private;
>  	if (private->number != num_counters) {
>  		ret = -EINVAL;
>  		goto unlock_up_free;
>  	}
>  
> -	preempt_disable();
> -	i = 0;
>  	/* Choose the copy that is on our node */
> -	loc_cpu_entry = private->entries[smp_processor_id()];
> +	cpu = raw_smp_processor_id();
> +	spin_lock_bh(&per_cpu(arp_tables_lock, cpu).lock);
> +	loc_cpu_entry = private->entries[cpu];
> +	i = 0;
>  	ARPT_ENTRY_ITERATE(loc_cpu_entry,
>  			   private->size,
>  			   add_counter_to_entry,
>  			   paddc,
>  			   &i);
> -	preempt_enable();
> +	spin_unlock_bh(&per_cpu(arp_tables_lock, cpu).lock);
> +
>   unlock_up_free:
> -	mutex_unlock(&t->lock);
>  
>  	xt_table_unlock(t);
>  	module_put(t->me);
> @@ -1923,7 +1881,10 @@ static struct pernet_operations arp_tables_net_ops = {
>  
>  static int __init arp_tables_init(void)
>  {
> -	int ret;
> +	int cpu, ret;
> +
> +	for_each_possible_cpu(cpu)
> +		spin_lock_init(&per_cpu(arp_tables_lock, cpu).lock);
>  
>  	ret = register_pernet_subsys(&arp_tables_net_ops);
>  	if (ret < 0)
> diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
> index 810c0b6..1368b6d 100644
> --- a/net/ipv4/netfilter/ip_tables.c
> +++ b/net/ipv4/netfilter/ip_tables.c
> @@ -297,6 +297,12 @@ static void trace_packet(struct sk_buff *skb,
>  }
>  #endif
>  
> +struct rec_lock {
> +	spinlock_t lock;
> +	int	   count; /* recursion count */
> +};
> +static DEFINE_PER_CPU(struct rec_lock, ip_tables_lock);
> +
>  /* Returns one of the generic firewall policies, like NF_ACCEPT. */
>  unsigned int
>  ipt_do_table(struct sk_buff *skb,
> @@ -317,6 +323,7 @@ ipt_do_table(struct sk_buff *skb,
>  	struct xt_table_info *private;
>  	struct xt_match_param mtpar;
>  	struct xt_target_param tgpar;
> +	struct rec_lock *rl;
>  
>  	/* Initialization */
>  	ip = ip_hdr(skb);
> @@ -341,7 +348,12 @@ ipt_do_table(struct sk_buff *skb,
>  
>  	rcu_read_lock_bh();
>  	private = rcu_dereference(table->private);
> -	table_base = rcu_dereference(private->entries[smp_processor_id()]);
> +
> +	rl = &__get_cpu_var(ip_tables_lock);
> +	if (likely(rl->count++ == 0))
> +		spin_lock(&rl->lock);
> +
> +	table_base = private->entries[smp_processor_id()];
>  
>  	e = get_entry(table_base, private->hook_entry[hook]);
>  
> @@ -436,7 +448,8 @@ ipt_do_table(struct sk_buff *skb,
>  			e = (void *)e + e->next_offset;
>  		}
>  	} while (!hotdrop);
> -
> +	if (likely(--rl->count == 0))
> +		spin_unlock(&rl->lock);
>  	rcu_read_unlock_bh();
>  
>  #ifdef DEBUG_ALLOW_ALL
> @@ -902,75 +915,25 @@ get_counters(const struct xt_table_info *t,
>  	curcpu = raw_smp_processor_id();
>  
>  	i = 0;
> +	spin_lock_bh(&per_cpu(ip_tables_lock, curcpu).lock);
>  	IPT_ENTRY_ITERATE(t->entries[curcpu],
>  			  t->size,
>  			  set_entry_to_counter,
>  			  counters,
>  			  &i);
> +	spin_unlock_bh(&per_cpu(ip_tables_lock, curcpu).lock);
>  
>  	for_each_possible_cpu(cpu) {
>  		if (cpu == curcpu)
>  			continue;
>  		i = 0;
> +		spin_lock_bh(&per_cpu(ip_tables_lock, cpu).lock);
>  		IPT_ENTRY_ITERATE(t->entries[cpu],
>  				  t->size,
>  				  add_entry_to_counter,
>  				  counters,
>  				  &i);
> -	}
> -
> -}
> -
> -/* We're lazy, and add to the first CPU; overflow works its fey magic
> - * and everything is OK. */
> -static int
> -add_counter_to_entry(struct ipt_entry *e,
> -		     const struct xt_counters addme[],
> -		     unsigned int *i)
> -{
> -	ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
> -
> -	(*i)++;
> -	return 0;
> -}
> -
> -/* Take values from counters and add them back onto the current cpu */
> -static void put_counters(struct xt_table_info *t,
> -			 const struct xt_counters counters[])
> -{
> -	unsigned int i, cpu;
> -
> -	local_bh_disable();
> -	cpu = smp_processor_id();
> -	i = 0;
> -	IPT_ENTRY_ITERATE(t->entries[cpu],
> -			  t->size,
> -			  add_counter_to_entry,
> -			  counters,
> -			  &i);
> -	local_bh_enable();
> -}
> -
> -
> -static inline int
> -zero_entry_counter(struct ipt_entry *e, void *arg)
> -{
> -	e->counters.bcnt = 0;
> -	e->counters.pcnt = 0;
> -	return 0;
> -}
> -
> -static void
> -clone_counters(struct xt_table_info *newinfo, const struct xt_table_info *info)
> -{
> -	unsigned int cpu;
> -	const void *loc_cpu_entry = info->entries[raw_smp_processor_id()];
> -
> -	memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
> -	for_each_possible_cpu(cpu) {
> -		memcpy(newinfo->entries[cpu], loc_cpu_entry, info->size);
> -		IPT_ENTRY_ITERATE(newinfo->entries[cpu], newinfo->size,
> -				  zero_entry_counter, NULL);
> +		spin_unlock_bh(&per_cpu(ip_tables_lock, cpu).lock);
>  	}
>  }
>  
> @@ -979,7 +942,6 @@ static struct xt_counters * alloc_counters(struct xt_table *table)
>  	unsigned int countersize;
>  	struct xt_counters *counters;
>  	struct xt_table_info *private = table->private;
> -	struct xt_table_info *info;
>  
>  	/* We need atomic snapshot of counters: rest doesn't change
>  	   (other than comefrom, which userspace doesn't care
> @@ -988,30 +950,11 @@ static struct xt_counters * alloc_counters(struct xt_table *table)
>  	counters = vmalloc_node(countersize, numa_node_id());
>  
>  	if (counters == NULL)
> -		goto nomem;
> -
> -	info = xt_alloc_table_info(private->size);
> -	if (!info)
> -		goto free_counters;
> -
> -	clone_counters(info, private);
> -
> -	mutex_lock(&table->lock);
> -	xt_table_entry_swap_rcu(private, info);
> -	synchronize_net();	/* Wait until smoke has cleared */
> +		return ERR_PTR(-ENOMEM);
>  
> -	get_counters(info, counters);
> -	put_counters(private, counters);
> -	mutex_unlock(&table->lock);
> -
> -	xt_free_table_info(info);
> +	get_counters(private, counters);
>  
>  	return counters;
> -
> - free_counters:
> -	vfree(counters);
> - nomem:
> -	return ERR_PTR(-ENOMEM);
>  }
>  
>  static int
> @@ -1377,6 +1320,18 @@ do_replace(struct net *net, void __user *user, unsigned int len)
>  	return ret;
>  }
>  
> +/* We're lazy, and add to the first CPU; overflow works its fey magic
> + * and everything is OK. */
> +static int
> +add_counter_to_entry(struct ipt_entry *e,
> +		     const struct xt_counters addme[],
> +		     unsigned int *i)
> +{
> +	ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
> +
> +	(*i)++;
> +	return 0;
> +}
>  
>  static int
>  do_add_counters(struct net *net, void __user *user, unsigned int len, int compat)
> @@ -1386,7 +1341,7 @@ do_add_counters(struct net *net, void __user *user, unsigned int len, int compat
>  	struct xt_counters *paddc;
>  	unsigned int num_counters;
>  	const char *name;
> -	int size;
> +	int cpu, size;
>  	void *ptmp;
>  	struct xt_table *t;
>  	const struct xt_table_info *private;
> @@ -1437,25 +1392,25 @@ do_add_counters(struct net *net, void __user *user, unsigned int len, int compat
>  		goto free;
>  	}
>  
> -	mutex_lock(&t->lock);
>  	private = t->private;
>  	if (private->number != num_counters) {
>  		ret = -EINVAL;
>  		goto unlock_up_free;
>  	}
>  
> -	preempt_disable();
> -	i = 0;
>  	/* Choose the copy that is on our node */
> -	loc_cpu_entry = private->entries[raw_smp_processor_id()];
> +	cpu = raw_smp_processor_id();
> +	spin_lock_bh(&per_cpu(ip_tables_lock, cpu).lock);
> +	loc_cpu_entry = private->entries[cpu];
> +	i = 0;
>  	IPT_ENTRY_ITERATE(loc_cpu_entry,
>  			  private->size,
>  			  add_counter_to_entry,
>  			  paddc,
>  			  &i);
> -	preempt_enable();
> +	spin_unlock_bh(&per_cpu(ip_tables_lock, cpu).lock);
> +
>   unlock_up_free:
> -	mutex_unlock(&t->lock);
>  	xt_table_unlock(t);
>  	module_put(t->me);
>   free:
> @@ -2272,7 +2227,10 @@ static struct pernet_operations ip_tables_net_ops = {
>  
>  static int __init ip_tables_init(void)
>  {
> -	int ret;
> +	int cpu, ret;
> +
> +	for_each_possible_cpu(cpu)
> +		spin_lock_init(&per_cpu(ip_tables_lock, cpu).lock);
>  
>  	ret = register_pernet_subsys(&ip_tables_net_ops);
>  	if (ret < 0)
> diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
> index 800ae85..5b03479 100644
> --- a/net/ipv6/netfilter/ip6_tables.c
> +++ b/net/ipv6/netfilter/ip6_tables.c
> @@ -329,6 +329,12 @@ static void trace_packet(struct sk_buff *skb,
>  }
>  #endif
>  
> +struct rec_lock {
> +	spinlock_t lock;
> +	int	   count; /* recursion count */
> +};
> +static DEFINE_PER_CPU(struct rec_lock, ip6_tables_lock);
> +
>  /* Returns one of the generic firewall policies, like NF_ACCEPT. */
>  unsigned int
>  ip6t_do_table(struct sk_buff *skb,
> @@ -347,6 +353,7 @@ ip6t_do_table(struct sk_buff *skb,
>  	struct xt_table_info *private;
>  	struct xt_match_param mtpar;
>  	struct xt_target_param tgpar;
> +	struct rec_lock *rl;
>  
>  	/* Initialization */
>  	indev = in ? in->name : nulldevname;
> @@ -367,7 +374,12 @@ ip6t_do_table(struct sk_buff *skb,
>  
>  	rcu_read_lock_bh();
>  	private = rcu_dereference(table->private);
> -	table_base = rcu_dereference(private->entries[smp_processor_id()]);
> +
> +	rl = &__get_cpu_var(ip_tables_lock);
> +	if (likely(rl->count++ == 0))
> +		spin_lock(&rl->lock);
> +
> +	table_base = private->entries[smp_processor_id()];
>  
>  	e = get_entry(table_base, private->hook_entry[hook]);
>  
> @@ -467,6 +479,8 @@ ip6t_do_table(struct sk_buff *skb,
>  	((struct ip6t_entry *)table_base)->comefrom = NETFILTER_LINK_POISON;
>  #endif
>  	rcu_read_unlock_bh();
> +	if (likely(--rl->count == 0))
> +		spin_unlock(&rl->lock);
>  
>  #ifdef DEBUG_ALLOW_ALL
>  	return NF_ACCEPT;
> @@ -931,73 +945,25 @@ get_counters(const struct xt_table_info *t,
>  	curcpu = raw_smp_processor_id();
>  
>  	i = 0;
> +	spin_lock_bh(&per_cpu(ip6_tables_lock, curcpu).lock);
>  	IP6T_ENTRY_ITERATE(t->entries[curcpu],
>  			   t->size,
>  			   set_entry_to_counter,
>  			   counters,
>  			   &i);
> +	spin_unlock_bh(&per_cpu(ip6_tables_lock, curcpu).lock);
>  
>  	for_each_possible_cpu(cpu) {
>  		if (cpu == curcpu)
>  			continue;
>  		i = 0;
> +		spin_lock_bh(&per_cpu(ip6_tables_lock, cpu).lock);
>  		IP6T_ENTRY_ITERATE(t->entries[cpu],
>  				  t->size,
>  				  add_entry_to_counter,
>  				  counters,
>  				  &i);
> -	}
> -}
> -
> -/* We're lazy, and add to the first CPU; overflow works its fey magic
> - * and everything is OK. */
> -static int
> -add_counter_to_entry(struct ip6t_entry *e,
> -		     const struct xt_counters addme[],
> -		     unsigned int *i)
> -{
> -	ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
> -
> -	(*i)++;
> -	return 0;
> -}
> -
> -/* Take values from counters and add them back onto the current cpu */
> -static void put_counters(struct xt_table_info *t,
> -			 const struct xt_counters counters[])
> -{
> -	unsigned int i, cpu;
> -
> -	local_bh_disable();
> -	cpu = smp_processor_id();
> -	i = 0;
> -	IP6T_ENTRY_ITERATE(t->entries[cpu],
> -			   t->size,
> -			   add_counter_to_entry,
> -			   counters,
> -			   &i);
> -	local_bh_enable();
> -}
> -
> -static inline int
> -zero_entry_counter(struct ip6t_entry *e, void *arg)
> -{
> -	e->counters.bcnt = 0;
> -	e->counters.pcnt = 0;
> -	return 0;
> -}
> -
> -static void
> -clone_counters(struct xt_table_info *newinfo, const struct xt_table_info *info)
> -{
> -	unsigned int cpu;
> -	const void *loc_cpu_entry = info->entries[raw_smp_processor_id()];
> -
> -	memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
> -	for_each_possible_cpu(cpu) {
> -		memcpy(newinfo->entries[cpu], loc_cpu_entry, info->size);
> -		IP6T_ENTRY_ITERATE(newinfo->entries[cpu], newinfo->size,
> -				   zero_entry_counter, NULL);
> +		spin_unlock_bh(&per_cpu(ip6_tables_lock, cpu).lock);
>  	}
>  }
>  
> @@ -1006,7 +972,6 @@ static struct xt_counters *alloc_counters(struct xt_table *table)
>  	unsigned int countersize;
>  	struct xt_counters *counters;
>  	struct xt_table_info *private = table->private;
> -	struct xt_table_info *info;
>  
>  	/* We need atomic snapshot of counters: rest doesn't change
>  	   (other than comefrom, which userspace doesn't care
> @@ -1015,30 +980,11 @@ static struct xt_counters *alloc_counters(struct xt_table *table)
>  	counters = vmalloc_node(countersize, numa_node_id());
>  
>  	if (counters == NULL)
> -		goto nomem;
> -
> -	info = xt_alloc_table_info(private->size);
> -	if (!info)
> -		goto free_counters;
> -
> -	clone_counters(info, private);
> -
> -	mutex_lock(&table->lock);
> -	xt_table_entry_swap_rcu(private, info);
> -	synchronize_net();	/* Wait until smoke has cleared */
> +		return ERR_PTR(-ENOMEM);
>  
> -	get_counters(info, counters);
> -	put_counters(private, counters);
> -	mutex_unlock(&table->lock);
> -
> -	xt_free_table_info(info);
> +	get_counters(private, counters);
>  
>  	return counters;
> -
> - free_counters:
> -	vfree(counters);
> - nomem:
> -	return ERR_PTR(-ENOMEM);
>  }
>  
>  static int
> @@ -1405,6 +1351,19 @@ do_replace(struct net *net, void __user *user, unsigned int len)
>  	return ret;
>  }
>  
> +/* We're lazy, and add to the first CPU; overflow works its fey magic
> + * and everything is OK. */
> +static int
> +add_counter_to_entry(struct ip6t_entry *e,
> +		     const struct xt_counters addme[],
> +		     unsigned int *i)
> +{
> +	ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
> +
> +	(*i)++;
> +	return 0;
> +}
> +
>  static int
>  do_add_counters(struct net *net, void __user *user, unsigned int len,
>  		int compat)
> @@ -1465,25 +1424,26 @@ do_add_counters(struct net *net, void __user *user, unsigned int len,
>  		goto free;
>  	}
>  
> -	mutex_lock(&t->lock);
>  	private = t->private;
>  	if (private->number != num_counters) {
>  		ret = -EINVAL;
>  		goto unlock_up_free;
>  	}
>  
> -	preempt_disable();
> -	i = 0;
> +	local_bh_disable();
>  	/* Choose the copy that is on our node */
> -	loc_cpu_entry = private->entries[raw_smp_processor_id()];
> +	spin_lock(&__get_cpu_var(ip6_tables_lock).lock);
> +	loc_cpu_entry = private->entries[smp_processor_id()];
> +	i = 0;
>  	IP6T_ENTRY_ITERATE(loc_cpu_entry,
>  			  private->size,
>  			  add_counter_to_entry,
>  			  paddc,
>  			  &i);
> -	preempt_enable();
> +	spin_unlock(&__get_cpu_var(ip6_tables_lock).lock);
> +	local_bh_enable();
> +
>   unlock_up_free:
> -	mutex_unlock(&t->lock);
>  	xt_table_unlock(t);
>  	module_put(t->me);
>   free:
> @@ -2298,7 +2258,10 @@ static struct pernet_operations ip6_tables_net_ops = {
>  
>  static int __init ip6_tables_init(void)
>  {
> -	int ret;
> +	int cpu, ret;
> +
> +	for_each_possible_cpu(cpu)
> +		spin_lock_init(&per_cpu(ip6_tables_lock, cpu).lock);
>  
>  	ret = register_pernet_subsys(&ip6_tables_net_ops);
>  	if (ret < 0)
> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> index 509a956..adc1b11 100644
> --- a/net/netfilter/x_tables.c
> +++ b/net/netfilter/x_tables.c
> @@ -625,20 +625,6 @@ void xt_free_table_info(struct xt_table_info *info)
>  }
>  EXPORT_SYMBOL(xt_free_table_info);
>  
> -void xt_table_entry_swap_rcu(struct xt_table_info *oldinfo,
> -			     struct xt_table_info *newinfo)
> -{
> -	unsigned int cpu;
> -
> -	for_each_possible_cpu(cpu) {
> -		void *p = oldinfo->entries[cpu];
> -		rcu_assign_pointer(oldinfo->entries[cpu], newinfo->entries[cpu]);
> -		newinfo->entries[cpu] = p;
> -	}
> -
> -}
> -EXPORT_SYMBOL_GPL(xt_table_entry_swap_rcu);
> -
>  /* Find table by name, grabs mutex & ref.  Returns ERR_PTR() on error. */
>  struct xt_table *xt_find_table_lock(struct net *net, u_int8_t af,
>  				    const char *name)
> @@ -682,26 +668,21 @@ xt_replace_table(struct xt_table *table,
>  	      struct xt_table_info *newinfo,
>  	      int *error)
>  {
> -	struct xt_table_info *oldinfo, *private;
> +	struct xt_table_info *private;
>  
>  	/* Do the substitution. */
> -	mutex_lock(&table->lock);
>  	private = table->private;
>  	/* Check inside lock: is the old number correct? */
>  	if (num_counters != private->number) {
>  		duprintf("num_counters != table->private->number (%u/%u)\n",
>  			 num_counters, private->number);
> -		mutex_unlock(&table->lock);
>  		*error = -EAGAIN;
>  		return NULL;
>  	}
> -	oldinfo = private;
>  	rcu_assign_pointer(table->private, newinfo);
> -	newinfo->initial_entries = oldinfo->initial_entries;
> -	mutex_unlock(&table->lock);
> +	newinfo->initial_entries = private->initial_entries;
>  
> -	synchronize_net();
> -	return oldinfo;
> +	return private;
>  }
>  EXPORT_SYMBOL_GPL(xt_replace_table);
>  
> @@ -734,7 +715,6 @@ struct xt_table *xt_register_table(struct net *net, struct xt_table *table,
>  
>  	/* Simplifies replace_table code. */
>  	table->private = bootstrap;
> -	mutex_init(&table->lock);
>  
>  	if (!xt_replace_table(table, 0, newinfo, &ret))
>  		goto unlock;
> 
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