Date:	Sun, 26 Apr 2009 14:56:46 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	David Miller <davem@...emloft.net>,
	Jarek Poplawski <jarkao2@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	paulmck@...ux.vnet.ibm.com, Evgeniy Polyakov <zbr@...emap.net>,
	kaber@...sh.net, jeff.chua.linux@...il.com, laijs@...fujitsu.com,
	jengelh@...ozas.de, r000n@...0n.net, linux-kernel@...r.kernel.org,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	benh@...nel.crashing.org
Subject: Re: [PATCH] netfilter: use per-CPU recursive lock {XV}

* Eric Dumazet (dada1@...mosbay.com) wrote:
> From: Stephen Hemminger <shemminger@...tta.com>
> 
> > Epilogue due to master Jarek. Lockdep carest not about the locking
> > doth bestowed. Therefore no keys are needed.
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> 
> So far, so good, should be ready for inclusion now, nobody complained :)
> 
> I include the final patch, merge of your last two patches.
> 
> David, could you please review it once again and apply it if it's OK ?
> 
> Thanks to all for your help and patience
> 
> [PATCH] netfilter: use per-CPU recursive lock {XV}

Hi Eric,

Please... could you rename this patch according to Linus'comments ?

Suitable name would probably be :

[PATCH] netfilter: use bh disabling with per-cpu read-write lock

> 
> In days of old in 2.6.29, netfilter did locketh using a 
> lock of the reader kind when doing its table business, and do
> a writer when with pen in hand like a overworked accountant
> did replace the tables. This sucketh and caused the single
> lock to fly back and forth like a poor errant boy.
> 
> But then netfilter was blessed with RCU and the performance
> was divine, but alas there were those that suffered for
> trying to replace their many rules one at a time.
> 
> So now RCU must be vanquished from the scene, and better
> chastity belts be placed upon this valuable asset most dear.
> The locks that were but one are now replaced by one per suitor.
> 
> The repair was made after much discussion involving
> Eric the wise, and Linus the foul. With flowers springing
> up amid the thorns some peace has finally prevailed and
> all is soothed. This patch and purple prose was penned by
> in honor of "Talk like Shakespeare" day.
> 
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
> ---
> What hath changed over the last two setting suns:
> 
>   * more words, mostly correct...
> 
>   * no need to locketh for writeh on current cpu tis 
>     always so
> 
>   * the locking of all cpu's on replace is always done as
>     part of the get_counters cycle, so the sychronize swip
>     in replace tables is gone with only a comment remaing
> 
>   * Epilogue due to master Jarek. Lockdep carest not about
>     the locking doth bestowed. Therefore no keys are needed.
> 
>  include/linux/netfilter/x_tables.h |   55 ++++++++++-
>  net/ipv4/netfilter/arp_tables.c    |  125 +++++++-------------------
>  net/ipv4/netfilter/ip_tables.c     |  126 +++++++--------------------
>  net/ipv6/netfilter/ip6_tables.c    |  123 +++++++-------------------
>  net/netfilter/x_tables.c           |   50 +++++-----
>  5 files changed, 183 insertions(+), 296 deletions(-)
> 
> diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
> index 7b1a652..511debb 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 +431,56 @@ 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);
> +
> +/*
> + * Per-CPU read/write lock associated with per-cpu table entries.
> + * This is not a general solution but makes reader locking fast since
> + * there is no shared variable to cause cache ping-pong; but adds an
> + * additional write-side penalty since update must lock all
> + * possible CPU's.
> + *
> + * Read lock is used by ip/arp/ip6 tables rule processing which runs per-cpu.
> + * It needs to ensure that the rules are not being changed while packet
> + * is being processed. In some cases, the read lock will be acquired
> + * twice on the same CPU; this is okay because read locks handle nesting.
> + *
> + * Write lock is used in two cases:
> + *    1. reading counter values
> + *       all readers need to be stopped and the per-CPU values are summed.
> + *
> + *    2. replacing tables
> + *       any readers that are using the old tables have to complete
> + *       before freeing the old table. This is handled by reading
> + *	  as a side effect of reading counters

Stating that the write lock must _always_ be taken with bh disabled
might not hurt here.

> + */
> +DECLARE_PER_CPU(rwlock_t, xt_info_locks);
> +
> +static inline void xt_info_rdlock_bh(void)
> +{
> +	/*
> +	 * Note: can not use read_lock_bh(&__get_cpu_var(xt_info_locks))
> +	 * because need to ensure that preemption is disable before
> +	 * acquiring per-cpu-variable, so do it as a two step process
> +	 */
> +	local_bh_disable();
> +	read_lock(&__get_cpu_var(xt_info_locks));
> +}
> +
> +static inline void xt_info_rdunlock_bh(void)
> +{
> +	read_unlock_bh(&__get_cpu_var(xt_info_locks));
> +}
> +
> +static inline void xt_info_wrlock(unsigned int cpu)
> +{
> +	write_lock(&per_cpu(xt_info_locks, cpu));
> +}
> +
> +static inline void xt_info_wrunlock(unsigned int cpu)
> +{
> +
> +	write_unlock(&per_cpu(xt_info_locks, cpu));
> +}
>  
>  /*
>   * 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..831fe18 100644
> --- a/net/ipv4/netfilter/arp_tables.c
> +++ b/net/ipv4/netfilter/arp_tables.c
> @@ -253,9 +253,9 @@ unsigned int arpt_do_table(struct sk_buff *skb,
>  	indev = in ? in->name : nulldevname;
>  	outdev = out ? out->name : nulldevname;
>  
> -	rcu_read_lock_bh();
> -	private = rcu_dereference(table->private);
> -	table_base = rcu_dereference(private->entries[smp_processor_id()]);
> +	xt_info_rdlock_bh();
> +	private = table->private;
> +	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 +273,7 @@ unsigned int arpt_do_table(struct sk_buff *skb,
>  
>  			hdr_len = sizeof(*arp) + (2 * sizeof(struct in_addr)) +
>  				(2 * skb->dev->addr_len);
> +

This is not a whitespace cleanup patch.

>  			ADD_COUNTER(e->counters, hdr_len, 1);
>  
>  			t = arpt_get_target(e);
> @@ -328,8 +329,7 @@ unsigned int arpt_do_table(struct sk_buff *skb,
>  			e = (void *)e + e->next_offset;
>  		}
>  	} while (!hotdrop);
> -

Whitespace cleanup ?

> -	rcu_read_unlock_bh();
> +	xt_info_rdunlock_bh();
>  
>  	if (hotdrop)
>  		return NF_DROP;
> @@ -711,9 +711,12 @@ static void get_counters(const struct xt_table_info *t,
>  	/* Instead of clearing (by a previous call to memset())
>  	 * the counters and using adds, we set the counters
>  	 * with data used by 'current' CPU
> -	 * We dont care about preemption here.
> +	 *
> +	 * Bottom half has to be disabled to prevent deadlock
> +	 * if new softirq were to run and call ipt_do_table
>  	 */
> -	curcpu = raw_smp_processor_id();
> +	local_bh_disable();
> +	curcpu = smp_processor_id();
>  
>  	i = 0;
>  	ARPT_ENTRY_ITERATE(t->entries[curcpu],
> @@ -726,73 +729,22 @@ static void get_counters(const struct xt_table_info *t,
>  		if (cpu == curcpu)
>  			continue;
>  		i = 0;
> +		xt_info_wrlock(cpu);
>  		ARPT_ENTRY_ITERATE(t->entries[cpu],
>  				   t->size,
>  				   add_entry_to_counter,
>  				   counters,
>  				   &i);
> +		xt_info_wrunlock(cpu);
>  	}
> -}
> -
> -
> -/* 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();
>  }

Did you really need to move add_counter_to_entry and put_counters in
this patch ? This also seems more like a cleanup to me, if it is even
one. It does make the patch harder to follow though.

>  
> -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);
> -	}
> -}
> -
>  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 +754,11 @@ 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 copy_entries_to_user(unsigned int total_size,
> @@ -1094,8 +1027,9 @@ static int __do_replace(struct net *net, const char *name,
>  	    (newinfo->number <= oldinfo->initial_entries))
>  		module_put(t->me);
>  
> -	/* Get the old counters. */
> +	/* Get the old counters, and synchronize with replace */
>  	get_counters(oldinfo, counters);
> +
>  	/* Decrease module usage counts and free resource */
>  	loc_cpu_old_entry = oldinfo->entries[raw_smp_processor_id()];
>  	ARPT_ENTRY_ITERATE(loc_cpu_old_entry, oldinfo->size, cleanup_entry,
> @@ -1165,10 +1099,23 @@ 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)
>  {
> -	unsigned int i;
> +	unsigned int i, curcpu;
>  	struct xt_counters_info tmp;
>  	struct xt_counters *paddc;
>  	unsigned int num_counters;
> @@ -1224,26 +1171,26 @@ static int do_add_counters(struct net *net, void __user *user, unsigned int len,
>  		goto free;
>  	}
>  
> -	mutex_lock(&t->lock);
> +	local_bh_disable();
>  	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()];
> +	curcpu = smp_processor_id();
> +	loc_cpu_entry = private->entries[curcpu];
> +	xt_info_wrlock(curcpu);
>  	ARPT_ENTRY_ITERATE(loc_cpu_entry,
>  			   private->size,
>  			   add_counter_to_entry,
>  			   paddc,
>  			   &i);
> -	preempt_enable();
> +	xt_info_wrunlock(curcpu);
>   unlock_up_free:
> -	mutex_unlock(&t->lock);
> -
> +	local_bh_enable();
>  	xt_table_unlock(t);
>  	module_put(t->me);
>   free:
> diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
> index 810c0b6..2ec8d72 100644
> --- a/net/ipv4/netfilter/ip_tables.c
> +++ b/net/ipv4/netfilter/ip_tables.c
> @@ -338,10 +338,9 @@ ipt_do_table(struct sk_buff *skb,
>  	tgpar.hooknum = hook;
>  
>  	IP_NF_ASSERT(table->valid_hooks & (1 << hook));
> -
> -	rcu_read_lock_bh();
> -	private = rcu_dereference(table->private);
> -	table_base = rcu_dereference(private->entries[smp_processor_id()]);
> +	xt_info_rdlock_bh();
> +	private = table->private;
> +	table_base = private->entries[smp_processor_id()];
>  
>  	e = get_entry(table_base, private->hook_entry[hook]);
>  
> @@ -436,8 +435,7 @@ ipt_do_table(struct sk_buff *skb,
>  			e = (void *)e + e->next_offset;
>  		}
>  	} while (!hotdrop);
> -
> -	rcu_read_unlock_bh();
> +	xt_info_rdunlock_bh();
>  
>  #ifdef DEBUG_ALLOW_ALL
>  	return NF_ACCEPT;
> @@ -896,10 +894,13 @@ get_counters(const struct xt_table_info *t,
>  
>  	/* Instead of clearing (by a previous call to memset())
>  	 * the counters and using adds, we set the counters
> -	 * with data used by 'current' CPU
> -	 * We dont care about preemption here.
> +	 * with data used by 'current' CPU.
> +	 *
> +	 * Bottom half has to be disabled to prevent deadlock
> +	 * if new softirq were to run and call ipt_do_table
>  	 */
> -	curcpu = raw_smp_processor_id();
> +	local_bh_disable();
> +	curcpu = smp_processor_id();
>  
>  	i = 0;
>  	IPT_ENTRY_ITERATE(t->entries[curcpu],
> @@ -912,74 +913,22 @@ get_counters(const struct xt_table_info *t,
>  		if (cpu == curcpu)
>  			continue;
>  		i = 0;
> +		xt_info_wrlock(cpu);
>  		IPT_ENTRY_ITERATE(t->entries[cpu],
>  				  t->size,
>  				  add_entry_to_counter,
>  				  counters,
>  				  &i);
> +		xt_info_wrunlock(cpu);
>  	}
> -
> -}
> -
> -/* 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);
> -	}
> -}
> -
>  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 +937,11 @@ static struct xt_counters * alloc_counters(struct xt_table *table)
>  	counters = vmalloc_node(countersize, numa_node_id());
>  
>  	if (counters == NULL)
> -		goto nomem;
> +		return ERR_PTR(-ENOMEM);
>  
> -	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 */
> -
> -	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
> @@ -1306,8 +1236,9 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks,
>  	    (newinfo->number <= oldinfo->initial_entries))
>  		module_put(t->me);
>  
> -	/* Get the old counters. */
> +	/* Get the old counters, and synchronize with replace */
>  	get_counters(oldinfo, counters);
> +
>  	/* Decrease module usage counts and free resource */
>  	loc_cpu_old_entry = oldinfo->entries[raw_smp_processor_id()];
>  	IPT_ENTRY_ITERATE(loc_cpu_old_entry, oldinfo->size, cleanup_entry,
> @@ -1377,11 +1308,23 @@ 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)
>  {
> -	unsigned int i;
> +	unsigned int i, curcpu;
>  	struct xt_counters_info tmp;
>  	struct xt_counters *paddc;
>  	unsigned int num_counters;
> @@ -1437,25 +1380,26 @@ do_add_counters(struct net *net, void __user *user, unsigned int len, int compat
>  		goto free;
>  	}
>  
> -	mutex_lock(&t->lock);
> +	local_bh_disable();
>  	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()];
> +	curcpu = smp_processor_id();
> +	loc_cpu_entry = private->entries[curcpu];
> +	xt_info_wrlock(curcpu);
>  	IPT_ENTRY_ITERATE(loc_cpu_entry,
>  			  private->size,
>  			  add_counter_to_entry,
>  			  paddc,
>  			  &i);
> -	preempt_enable();
> +	xt_info_wrunlock(curcpu);
>   unlock_up_free:
> -	mutex_unlock(&t->lock);
> +	local_bh_enable();
>  	xt_table_unlock(t);
>  	module_put(t->me);
>   free:
> diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
> index 800ae85..219e165 100644
> --- a/net/ipv6/netfilter/ip6_tables.c
> +++ b/net/ipv6/netfilter/ip6_tables.c
> @@ -365,9 +365,9 @@ ip6t_do_table(struct sk_buff *skb,
>  
>  	IP_NF_ASSERT(table->valid_hooks & (1 << hook));
>  
> -	rcu_read_lock_bh();
> -	private = rcu_dereference(table->private);
> -	table_base = rcu_dereference(private->entries[smp_processor_id()]);
> +	xt_info_rdlock_bh();
> +	private = table->private;
> +	table_base = private->entries[smp_processor_id()];
>  
>  	e = get_entry(table_base, private->hook_entry[hook]);
>  
> @@ -466,7 +466,7 @@ ip6t_do_table(struct sk_buff *skb,
>  #ifdef CONFIG_NETFILTER_DEBUG
>  	((struct ip6t_entry *)table_base)->comefrom = NETFILTER_LINK_POISON;
>  #endif
> -	rcu_read_unlock_bh();
> +	xt_info_rdunlock_bh();
>  
>  #ifdef DEBUG_ALLOW_ALL
>  	return NF_ACCEPT;
> @@ -926,9 +926,12 @@ get_counters(const struct xt_table_info *t,
>  	/* Instead of clearing (by a previous call to memset())
>  	 * the counters and using adds, we set the counters
>  	 * with data used by 'current' CPU
> -	 * We dont care about preemption here.
> +	 *
> +	 * Bottom half has to be disabled to prevent deadlock
> +	 * if new softirq were to run and call ipt_do_table
>  	 */
> -	curcpu = raw_smp_processor_id();
> +	local_bh_disable();
> +	curcpu = smp_processor_id();
>  
>  	i = 0;
>  	IP6T_ENTRY_ITERATE(t->entries[curcpu],
> @@ -941,72 +944,22 @@ get_counters(const struct xt_table_info *t,
>  		if (cpu == curcpu)
>  			continue;
>  		i = 0;
> +		xt_info_wrlock(cpu);
>  		IP6T_ENTRY_ITERATE(t->entries[cpu],
>  				  t->size,
>  				  add_entry_to_counter,
>  				  counters,
>  				  &i);
> +		xt_info_wrunlock(cpu);
>  	}
> -}
> -
> -/* 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);
> -	}
> -}
> -
>  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 +968,11 @@ static struct xt_counters *alloc_counters(struct xt_table *table)
>  	counters = vmalloc_node(countersize, numa_node_id());
>  
>  	if (counters == NULL)
> -		goto nomem;
> +		return ERR_PTR(-ENOMEM);
>  
> -	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 */
> -
> -	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
> @@ -1334,8 +1268,9 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks,
>  	    (newinfo->number <= oldinfo->initial_entries))
>  		module_put(t->me);
>  
> -	/* Get the old counters. */
> +	/* Get the old counters, and synchronize with replace */
>  	get_counters(oldinfo, counters);
> +
>  	/* Decrease module usage counts and free resource */
>  	loc_cpu_old_entry = oldinfo->entries[raw_smp_processor_id()];
>  	IP6T_ENTRY_ITERATE(loc_cpu_old_entry, oldinfo->size, cleanup_entry,
> @@ -1405,11 +1340,24 @@ 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)
>  {
> -	unsigned int i;
> +	unsigned int i, curcpu;
>  	struct xt_counters_info tmp;
>  	struct xt_counters *paddc;
>  	unsigned int num_counters;
> @@ -1465,25 +1413,28 @@ do_add_counters(struct net *net, void __user *user, unsigned int len,
>  		goto free;
>  	}
>  
> -	mutex_lock(&t->lock);
> +

Incorrect whiteline added.

> +	local_bh_disable();
>  	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()];
> +	curcpu = smp_processor_id();
> +	xt_info_wrlock(curcpu);
> +	loc_cpu_entry = private->entries[curcpu];
>  	IP6T_ENTRY_ITERATE(loc_cpu_entry,
>  			  private->size,
>  			  add_counter_to_entry,
>  			  paddc,
>  			  &i);
> -	preempt_enable();
> +	xt_info_wrunlock(curcpu);
> +

Inconsistent whiteline.

>   unlock_up_free:
> -	mutex_unlock(&t->lock);
> +	local_bh_enable();
>  	xt_table_unlock(t);
>  	module_put(t->me);
>   free:
> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> index 509a956..5807a4d 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)
> @@ -676,32 +662,43 @@ void xt_compat_unlock(u_int8_t af)
>  EXPORT_SYMBOL_GPL(xt_compat_unlock);
>  #endif
>  
> +DEFINE_PER_CPU(rwlock_t, xt_info_locks);
> +EXPORT_PER_CPU_SYMBOL_GPL(xt_info_locks);
> +
> +
>  struct xt_table_info *
>  xt_replace_table(struct xt_table *table,
>  	      unsigned int num_counters,
>  	      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);
> +	local_bh_disable();
>  	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);
> +		local_bh_enable();
>  		*error = -EAGAIN;
>  		return NULL;
>  	}
> -	oldinfo = private;
> -	rcu_assign_pointer(table->private, newinfo);
> -	newinfo->initial_entries = oldinfo->initial_entries;
> -	mutex_unlock(&table->lock);
>  

Whiteline.....

Mathieu

> -	synchronize_net();
> -	return oldinfo;
> +	table->private = newinfo;
> +	newinfo->initial_entries = private->initial_entries;
> +
> +	/*
> +	 * Even though table entries have now been swapped, other CPU's
> +	 * may still be using the old entries. This is okay, because
> +	 * resynchronization happens because of the locking done
> +	 * during the get_counters() routine.
> +	 */
> +	local_bh_enable();
> +
> +	return private;
>  }
>  EXPORT_SYMBOL_GPL(xt_replace_table);
>  
> @@ -734,7 +731,6 @@ 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;
> @@ -1147,7 +1143,11 @@ static struct pernet_operations xt_net_ops = {
>  
>  static int __init xt_init(void)
>  {
> -	int i, rv;
> +	unsigned int i;
> +	int rv;
> +
> +	for_each_possible_cpu(i)
> +		rwlock_init(&per_cpu(xt_info_locks, i));
>  
>  	xt = kmalloc(sizeof(struct xt_af) * NFPROTO_NUMPROTO, GFP_KERNEL);
>  	if (!xt)

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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