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Subject[PATCH] netfilter: use per-cpu spinlock rather than RCU (v3)
This is an 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.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

---
include/linux/netfilter/x_tables.h | 5 -
net/ipv4/netfilter/arp_tables.c | 112 +++++++++------------------------
net/ipv4/netfilter/ip_tables.c | 123 +++++++++++--------------------------
net/ipv6/netfilter/ip6_tables.c | 119 +++++++++++------------------------
net/netfilter/x_tables.c | 28 --------
5 files changed, 110 insertions(+), 277 deletions(-)
--- a/include/linux/netfilter/x_tables.h 2009-04-14 10:13:59.932292529 -0700
+++ b/include/linux/netfilter/x_tables.h 2009-04-14 10:14:04.121043331 -0700
@@ -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 *ne

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
--- a/net/ipv4/netfilter/ip_tables.c 2009-04-14 10:13:59.923167357 -0700
+++ b/net/ipv4/netfilter/ip_tables.c 2009-04-14 11:13:51.066830533 -0700
@@ -297,6 +297,8 @@ static void trace_packet(struct sk_buff
}
#endif

+static DEFINE_PER_CPU(spinlock_t, ip_tables_lock);
+
/* Returns one of the generic firewall policies, like NF_ACCEPT. */
unsigned int
ipt_do_table(struct sk_buff *skb,
@@ -339,9 +341,13 @@ ipt_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()]);
+ /* Not spin_lock_bh() because get_cpu_var
+ * needs to happen after preempt is disabled
+ */
+ local_bh_disable();
+ spin_lock(&__get_cpu_var(ip_tables_lock));
+ private = table->private;
+ table_base = private->entries[smp_processor_id()];

e = get_entry(table_base, private->hook_entry[hook]);

@@ -436,8 +442,8 @@ ipt_do_table(struct sk_buff *skb,
e = (void *)e + e->next_offset;
}
} while (!hotdrop);
-
- rcu_read_unlock_bh();
+ spin_unlock(&__get_cpu_var(ip_tables_lock));
+ local_bh_enable();

#ifdef DEBUG_ALLOW_ALL
return NF_ACCEPT;
@@ -902,75 +908,25 @@ get_counters(const struct xt_table_info
curcpu = raw_smp_processor_id();

i = 0;
+ spin_lock_bh(&per_cpu(ip_tables_lock, curcpu));
IPT_ENTRY_ITERATE(t->entries[curcpu],
t->size,
set_entry_to_counter,
counters,
&i);
+ spin_unlock_bh(&per_cpu(ip_tables_lock, curcpu));

for_each_possible_cpu(cpu) {
if (cpu == curcpu)
continue;
i = 0;
+ spin_lock_bh(&per_cpu(ip_tables_lock, cpu));
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));
}
}

@@ -979,7 +935,6 @@ static struct xt_counters * alloc_counte
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
@@ -990,26 +945,10 @@ static struct xt_counters * alloc_counte
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 */
-
- 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);
}
@@ -1377,6 +1316,18 @@ do_replace(struct net *net, void __user
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)
@@ -1437,25 +1388,26 @@ do_add_counters(struct net *net, void __
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()];
+ local_bh_disable();
+ spin_lock(&__get_cpu_var(ip_tables_lock));
+ loc_cpu_entry = private->entries[smp_processor_id()];
+ i = 0;
IPT_ENTRY_ITERATE(loc_cpu_entry,
private->size,
add_counter_to_entry,
paddc,
&i);
- preempt_enable();
+ spin_unlock(&__get_cpu_var(ip_tables_lock));
+ local_bh_enable();
+
unlock_up_free:
- mutex_unlock(&t->lock);
xt_table_unlock(t);
module_put(t->me);
free:
@@ -2272,7 +2224,10 @@ static struct pernet_operations ip_table

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));

ret = register_pernet_subsys(&ip_tables_net_ops);
if (ret < 0)
--- a/net/netfilter/x_tables.c 2009-04-14 10:13:59.901168540 -0700
+++ b/net/netfilter/x_tables.c 2009-04-14 10:14:04.123043143 -0700
@@ -625,20 +625,6 @@ void xt_free_table_info(struct xt_table_
}
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 +668,19 @@ 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);
-
- synchronize_net();
- return oldinfo;
+ newinfo->initial_entries = private->initial_entries;
+ return xchg(&table->private, newinfo);
}
EXPORT_SYMBOL_GPL(xt_replace_table);

@@ -734,7 +713,6 @@ struct xt_table *xt_register_table(struc

/* Simplifies replace_table code. */
table->private = bootstrap;
- mutex_init(&table->lock);

if (!xt_replace_table(table, 0, newinfo, &ret))
goto unlock;
--- a/net/ipv6/netfilter/ip6_tables.c 2009-04-14 10:13:59.909167832 -0700
+++ b/net/ipv6/netfilter/ip6_tables.c 2009-04-14 11:15:15.405141464 -0700
@@ -329,6 +329,8 @@ static void trace_packet(struct sk_buff
}
#endif

+static DEFINE_PER_CPU(spinlock_t, ip6_tables_lock);
+
/* Returns one of the generic firewall policies, like NF_ACCEPT. */
unsigned int
ip6t_do_table(struct sk_buff *skb,
@@ -365,9 +367,10 @@ 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()]);
+ local_bh_disable();
+ spin_lock(&__get_cpu_var(ip6_tables_lock));
+ private = table->private;
+ table_base = private->entries[smp_processor_id()];

e = get_entry(table_base, private->hook_entry[hook]);

@@ -466,7 +469,8 @@ 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();
+ spin_unlock(&__get_cpu_var(ip6_tables_lock));
+ local_bh_enable();

#ifdef DEBUG_ALLOW_ALL
return NF_ACCEPT;
@@ -931,73 +935,25 @@ get_counters(const struct xt_table_info
curcpu = raw_smp_processor_id();

i = 0;
+ spin_lock_bh(&per_cpu(ip6_tables_lock, curcpu));
IP6T_ENTRY_ITERATE(t->entries[curcpu],
t->size,
set_entry_to_counter,
counters,
&i);
+ spin_unlock_bh(&per_cpu(ip6_tables_lock, curcpu));

for_each_possible_cpu(cpu) {
if (cpu == curcpu)
continue;
i = 0;
+ spin_lock_bh(&per_cpu(ip6_tables_lock, cpu));
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));
}
}

@@ -1006,7 +962,6 @@ static struct xt_counters *alloc_counter
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
@@ -1017,26 +972,9 @@ static struct xt_counters *alloc_counter
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 */
-
- 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);
}
@@ -1405,6 +1343,19 @@ do_replace(struct net *net, void __user
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 +1416,26 @@ do_add_counters(struct net *net, void __
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));
+ 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));
+ local_bh_enable();
+
unlock_up_free:
- mutex_unlock(&t->lock);
xt_table_unlock(t);
module_put(t->me);
free:
@@ -2298,7 +2250,10 @@ static struct pernet_operations ip6_tabl

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));

ret = register_pernet_subsys(&ip6_tables_net_ops);
if (ret < 0)
--- a/net/ipv4/netfilter/arp_tables.c 2009-04-14 10:13:59.915167635 -0700
+++ b/net/ipv4/netfilter/arp_tables.c 2009-04-14 14:12:30.169955949 -0700
@@ -231,6 +231,8 @@ static inline struct arpt_entry *get_ent
return (struct arpt_entry *)(base + offset);
}

+static DEFINE_PER_CPU(spinlock_t, arp_tables_lock);
+
unsigned int arpt_do_table(struct sk_buff *skb,
unsigned int hook,
const struct net_device *in,
@@ -253,9 +255,10 @@ unsigned int arpt_do_table(struct sk_buf
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()]);
+ local_bh_disable();
+ spin_lock(&__get_cpu_var(arp_tables_lock));
+ 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]);
@@ -328,8 +331,8 @@ unsigned int arpt_do_table(struct sk_buf
e = (void *)e + e->next_offset;
}
} while (!hotdrop);
-
- rcu_read_unlock_bh();
+ spin_unlock(&__get_cpu_var(arp_tables_lock));
+ local_bh_enable();

if (hotdrop)
return NF_DROP;
@@ -716,74 +719,25 @@ static void get_counters(const struct xt
curcpu = raw_smp_processor_id();

i = 0;
+ spin_lock_bh(&per_cpu(arp_tables_lock, curcpu));
ARPT_ENTRY_ITERATE(t->entries[curcpu],
t->size,
set_entry_to_counter,
counters,
&i);
+ spin_unlock_bh(&per_cpu(arp_tables_lock, curcpu));

for_each_possible_cpu(cpu) {
if (cpu == curcpu)
continue;
i = 0;
+ spin_lock_bh(&per_cpu(arp_tables_lock, cpu));
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));
}
}

@@ -792,7 +746,6 @@ static struct xt_counters *alloc_counter
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
@@ -804,26 +757,10 @@ static struct xt_counters *alloc_counter
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 */
-
- 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);
}
@@ -1165,6 +1102,19 @@ static int do_replace(struct net *net, v
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)
{
@@ -1224,25 +1174,25 @@ static int do_add_counters(struct net *n
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 */
+ local_bh_disable();
+ spin_lock(&__get_cpu_var(arp_tables_lock));
loc_cpu_entry = private->entries[smp_processor_id()];
+ i = 0;
ARPT_ENTRY_ITERATE(loc_cpu_entry,
private->size,
add_counter_to_entry,
paddc,
&i);
- preempt_enable();
+ spin_unlock(&__get_cpu_var(arp_tables_lock));
+ local_bh_enable();
unlock_up_free:
- mutex_unlock(&t->lock);

xt_table_unlock(t);
module_put(t->me);
@@ -1923,7 +1873,10 @@ static struct pernet_operations arp_tabl

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));

ret = register_pernet_subsys(&arp_tables_net_ops);
if (ret < 0)

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