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Message-ID: <20090128073727.GB7732@linux.vnet.ibm.com>
Date: Tue, 27 Jan 2009 23:37:27 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Stephen Hemminger <shemminger@...tta.com>
Cc: David Miller <davem@...emloft.net>,
Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org
Subject: Re: [RFT 4/4] netfilter: convert x_tables to use RCU
On Tue, Jan 27, 2009 at 03:53:14PM -0800, Stephen Hemminger wrote:
> Replace existing reader/writer lock with Read-Copy-Update to
> elminate the overhead of a read lock on each incoming packet.
> This should reduce the overhead of iptables especially on SMP
> systems.
>
> The previous code used a reader-writer lock for two purposes.
> The first was to ensure that the xt_table_info reference was not in
> process of being changed. Since xt_table_info is only freed via one
> routine, it was a direct conversion to RCU.
>
> The other use of the reader-writer lock was to to block changes
> to counters while they were being read. This synchronization was
> fixed by the previous patch. But still need to make sure table info
> isn't going away. There are a couple of harmless races in reading
> the counters, but we always give a valid values they just aren't
> exactly frozen in time across all cpu's.
Looks good from an RCU perspective!
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
>
>
> ---
> include/linux/netfilter/x_tables.h | 10 ++++++--
> net/ipv4/netfilter/arp_tables.c | 12 +++++-----
> net/ipv4/netfilter/ip_tables.c | 12 +++++-----
> net/ipv6/netfilter/ip6_tables.c | 12 +++++-----
> net/netfilter/x_tables.c | 44 ++++++++++++++++++++++++++-----------
> 5 files changed, 58 insertions(+), 32 deletions(-)
>
> --- a/include/linux/netfilter/x_tables.h 2009-01-27 15:33:10.791377313 -0800
> +++ b/include/linux/netfilter/x_tables.h 2009-01-27 15:46:26.024128742 -0800
> @@ -352,8 +352,8 @@ struct xt_table
> /* What hooks you will enter on */
> unsigned int valid_hooks;
>
> - /* Lock for the curtain */
> - rwlock_t lock;
> + /* Lock for curtain */
> + spinlock_t lock;
>
> /* Man behind the curtain... */
> struct xt_table_info *private;
> @@ -383,6 +383,12 @@ struct xt_table_info
> unsigned int hook_entry[NF_INET_NUMHOOKS];
> unsigned int underflow[NF_INET_NUMHOOKS];
>
> + /* For the dustman... */
> + union {
> + struct rcu_head rcu;
> + struct work_struct work;
> + };
> +
> /* ipt_entry tables: one per CPU */
> /* Note : this field MUST be the last one, see XT_TABLE_INFO_SZ */
> void *entries[1];
> --- a/net/ipv4/netfilter/arp_tables.c 2009-01-27 15:45:34.566650540 -0800
> +++ b/net/ipv4/netfilter/arp_tables.c 2009-01-27 15:46:26.024128742 -0800
> @@ -237,8 +237,8 @@ unsigned int arpt_do_table(struct sk_buf
> indev = in ? in->name : nulldevname;
> outdev = out ? out->name : nulldevname;
>
> - read_lock_bh(&table->lock);
> - private = table->private;
> + rcu_read_lock_bh();
> + private = rcu_dereference(table->private);
> table_base = (void *)private->entries[smp_processor_id()];
> e = get_entry(table_base, private->hook_entry[hook]);
> back = get_entry(table_base, private->underflow[hook]);
> @@ -313,7 +313,7 @@ unsigned int arpt_do_table(struct sk_buf
> e = (void *)e + e->next_offset;
> }
> } while (!hotdrop);
> - read_unlock_bh(&table->lock);
> + rcu_read_unlock_bh();
>
> if (hotdrop)
> return NF_DROP;
> @@ -1154,8 +1154,8 @@ static int do_add_counters(struct net *n
> goto free;
> }
>
> - write_lock_bh(&t->lock);
> - private = t->private;
> + rcu_read_lock_bh();
> + private = rcu_dereference(t->private);
> if (private->number != num_counters) {
> ret = -EINVAL;
> goto unlock_up_free;
> @@ -1170,7 +1170,7 @@ static int do_add_counters(struct net *n
> paddc,
> &i);
> unlock_up_free:
> - write_unlock_bh(&t->lock);
> + rcu_read_unlock_bh();
> xt_table_unlock(t);
> module_put(t->me);
> free:
> --- a/net/ipv4/netfilter/ip_tables.c 2009-01-27 15:45:05.766673246 -0800
> +++ b/net/ipv4/netfilter/ip_tables.c 2009-01-27 15:46:26.024128742 -0800
> @@ -347,9 +347,9 @@ ipt_do_table(struct sk_buff *skb,
> mtpar.family = tgpar.family = NFPROTO_IPV4;
> tgpar.hooknum = hook;
>
> - read_lock_bh(&table->lock);
> + rcu_read_lock_bh();
> IP_NF_ASSERT(table->valid_hooks & (1 << hook));
> - private = table->private;
> + private = rcu_dereference(table->private);
> table_base = (void *)private->entries[smp_processor_id()];
> e = get_entry(table_base, private->hook_entry[hook]);
>
> @@ -447,7 +447,7 @@ ipt_do_table(struct sk_buff *skb,
> }
> } while (!hotdrop);
>
> - read_unlock_bh(&table->lock);
> + rcu_read_unlock_bh();
>
> #ifdef DEBUG_ALLOW_ALL
> return NF_ACCEPT;
> @@ -1399,8 +1399,8 @@ do_add_counters(struct net *net, void __
> goto free;
> }
>
> - write_lock_bh(&t->lock);
> - private = t->private;
> + rcu_read_lock_bh();
> + private = rcu_dereference(t->private);
> if (private->number != num_counters) {
> ret = -EINVAL;
> goto unlock_up_free;
> @@ -1415,7 +1415,7 @@ do_add_counters(struct net *net, void __
> paddc,
> &i);
> unlock_up_free:
> - write_unlock_bh(&t->lock);
> + rcu_read_unlock_bh();
> xt_table_unlock(t);
> module_put(t->me);
> free:
> --- a/net/ipv6/netfilter/ip6_tables.c 2009-01-27 15:45:22.262639173 -0800
> +++ b/net/ipv6/netfilter/ip6_tables.c 2009-01-27 15:46:26.028128353 -0800
> @@ -373,9 +373,9 @@ ip6t_do_table(struct sk_buff *skb,
> mtpar.family = tgpar.family = NFPROTO_IPV6;
> tgpar.hooknum = hook;
>
> - read_lock_bh(&table->lock);
> + rcu_read_lock_bh();
> IP_NF_ASSERT(table->valid_hooks & (1 << hook));
> - private = table->private;
> + private = rcu_dereference(table->private);
> table_base = (void *)private->entries[smp_processor_id()];
> e = get_entry(table_base, private->hook_entry[hook]);
>
> @@ -476,7 +476,7 @@ ip6t_do_table(struct sk_buff *skb,
> #ifdef CONFIG_NETFILTER_DEBUG
> ((struct ip6t_entry *)table_base)->comefrom = NETFILTER_LINK_POISON;
> #endif
> - read_unlock_bh(&table->lock);
> + rcu_read_unlock_bh();
>
> #ifdef DEBUG_ALLOW_ALL
> return NF_ACCEPT;
> @@ -1430,8 +1430,8 @@ do_add_counters(struct net *net, void __
> goto free;
> }
>
> - write_lock_bh(&t->lock);
> - private = t->private;
> + rcu_read_lock_bh();
> + private = rcu_dereference(t->private);
> if (private->number != num_counters) {
> ret = -EINVAL;
> goto unlock_up_free;
> @@ -1446,7 +1446,7 @@ do_add_counters(struct net *net, void __
> paddc,
> &i);
> unlock_up_free:
> - write_unlock_bh(&t->lock);
> + rcu_read_unlock_bh();
> xt_table_unlock(t);
> module_put(t->me);
> free:
> --- a/net/netfilter/x_tables.c 2009-01-27 15:14:06.004743434 -0800
> +++ b/net/netfilter/x_tables.c 2009-01-27 15:48:07.194667206 -0800
> @@ -611,17 +611,37 @@ struct xt_table_info *xt_alloc_table_inf
> }
> EXPORT_SYMBOL(xt_alloc_table_info);
>
> -void xt_free_table_info(struct xt_table_info *info)
> +/* callback to do free for vmalloc'd case */
> +static void xt_free_table_info_work(struct work_struct *arg)
> +{
> + struct xt_table_info *info = container_of(arg, struct xt_table_info, work);
> + unsigned int cpu;
> +
> + for_each_possible_cpu(cpu)
> + vfree(info->entries[cpu]);
> + kfree(info);
> +}
> +
> +/* callback to do free after all cpu's are done */
> +static void xt_free_table_info_rcu(struct rcu_head *arg)
> {
> - int cpu;
> + struct xt_table_info *info = container_of(arg, struct xt_table_info, rcu);
>
> - for_each_possible_cpu(cpu) {
> - if (info->size <= PAGE_SIZE)
> + if (info->size <= PAGE_SIZE) {
> + unsigned int cpu;
> + for_each_possible_cpu(cpu)
> kfree(info->entries[cpu]);
> - else
> - vfree(info->entries[cpu]);
> + kfree(info);
> + } else {
> + /* can't safely call vfree in current context */
> + INIT_WORK(&info->work, xt_free_table_info_work);
> + schedule_work(&info->work);
> }
> - kfree(info);
> +}
> +
> +void xt_free_table_info(struct xt_table_info *info)
> +{
> + call_rcu(&info->rcu, xt_free_table_info_rcu);
> }
> EXPORT_SYMBOL(xt_free_table_info);
>
> @@ -671,20 +691,20 @@ xt_replace_table(struct xt_table *table,
> struct xt_table_info *oldinfo, *private;
>
> /* Do the substitution. */
> - write_lock_bh(&table->lock);
> + spin_lock_bh(&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);
> - write_unlock_bh(&table->lock);
> + spin_unlock_bh(&table->lock);
> *error = -EAGAIN;
> return NULL;
> }
> oldinfo = private;
> - table->private = newinfo;
> + rcu_assign_pointer(table->private, newinfo);
> newinfo->initial_entries = oldinfo->initial_entries;
> - write_unlock_bh(&table->lock);
> + spin_unlock_bh(&table->lock);
>
> return oldinfo;
> }
> @@ -719,7 +739,7 @@ struct xt_table *xt_register_table(struc
>
> /* Simplifies replace_table code. */
> table->private = bootstrap;
> - rwlock_init(&table->lock);
> + spin_lock_init(&table->lock);
>
> if (!xt_replace_table(table, 0, newinfo, &ret))
> goto unlock;
>
> --
>
> --
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