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Date: Fri, 30 Jan 2009 08:02:39 +0100 From: Eric Dumazet <dada1@...mosbay.com> To: Stephen Hemminger <shemminger@...tta.com> CC: David Miller <davem@...emloft.net>, netdev@...r.kernel.org Subject: Re: [PATCH 5/5] netfilter: convert x_tables to use RCU Eric Dumazet a écrit : > Stephen Hemminger a écrit : >> On Fri, 30 Jan 2009 00:04:16 +0100 >> Eric Dumazet <dada1@...mosbay.com> wrote: >> >>> Stephen Hemminger a écrit : >>>> 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. >>>> >>>> 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 | 48 ++++++++++++++++++++++++++----------- >>>> 5 files changed, 60 insertions(+), 34 deletions(-) >>>> >>>> --- a/include/linux/netfilter/x_tables.h 2009-01-28 22:04:39.316517913 -0800 >>>> +++ b/include/linux/netfilter/x_tables.h 2009-01-28 22:14:54.648490491 -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; >>>> @@ -386,6 +386,12 @@ struct xt_table_info >>>> /* Secret compartment */ >>>> seqcount_t *seq; >>>> >>>> + /* 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 */ >>>> char *entries[1]; >>>> --- a/net/ipv4/netfilter/arp_tables.c 2009-01-28 22:13:16.423490077 -0800 >>>> +++ b/net/ipv4/netfilter/arp_tables.c 2009-01-28 22:14:54.648490491 -0800 >>>> @@ -238,8 +238,8 @@ 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()]; >>>> seq = per_cpu_ptr(private->seq, smp_processor_id()); >>>> e = get_entry(table_base, private->hook_entry[hook]); >>>> @@ -315,7 +315,7 @@ 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; >>>> @@ -1163,8 +1163,8 @@ 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; >>>> @@ -1179,7 +1179,7 @@ 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 2009-01-28 22:06:10.596739805 -0800 >>>> +++ b/net/ipv4/netfilter/ip_tables.c 2009-01-28 22:14:54.648490491 -0800 >>>> @@ -348,9 +348,9 @@ 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()]; >>>> seq = per_cpu_ptr(private->seq, smp_processor_id()); >>>> e = get_entry(table_base, private->hook_entry[hook]); >>>> @@ -449,7 +449,7 @@ 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; >>>> @@ -1408,8 +1408,8 @@ 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); >>> I feel litle bit nervous seeing a write_lock_bh() changed to a rcu_read_lock() >> Facts, it is only updating entries on current cpu > > Yes, like done in ipt_do_table() ;) > > Fact is we need to tell other threads, running on other cpus, that an update > of our entries is running. > > Let me check if your v4 and xt_counters abstraction already solved this problem. Hum, I just checked and indeed there is a problem... #define SUM_COUNTER(s,c) do { (s).bcnt += (c).bcnt; (s).pcnt += (c).pcnt; } while(0) need to be changed to use #define SUM_COUNTER(s, c) do { xt_incr_counter(s, (c).cnt, (c).pcnt);} while (0) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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