Re: [PATCH net-next] netfilter: x_table: speedup compat operations

Pablo Neira Ayuso
2011-01-12T20:44:46Z

On 18/12/10 18:35, Eric Dumazet wrote:
> One iptables invocation with 135000 rules takes 35 seconds of cpu time
> on a recent server, using a 32bit distro and a 64bit kernel.
>
> We eventually trigger NMI/RCU watchdog.
>
> INFO: rcu_sched_state detected stall on CPU 3 (t=6000 jiffies)
>
> COMPAT mode has quadratic behavior and consume 16 bytes of memory per
> rule.
>
> Switch the xt_compat algos to use an array instead of list, and use a
> binary search to locate an offset in the sorted array.
>
> This halves memory need (8 bytes per rule), and removes quadratic
> behavior [ O(N*N) -> O(N*log2(N)) ]
>
> Time of iptables goes from 35 s to 150 ms.
>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> ---
> include/linux/netfilter/x_tables.h | 3
> net/bridge/netfilter/ebtables.c | 1
> net/ipv4/netfilter/arp_tables.c | 2
> net/ipv4/netfilter/ip_tables.c | 2
> net/ipv6/netfilter/ip6_tables.c | 2
> net/netfilter/x_tables.c | 82 +++++++++++++++------------
> 6 files changed, 57 insertions(+), 35 deletions(-)
>
> diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
> index 742bec0..0f04d98 100644
> --- a/include/linux/netfilter/x_tables.h
> +++ b/include/linux/netfilter/x_tables.h
> @@ -611,8 +611,9 @@ struct _compat_xt_align {
> extern void xt_compat_lock(u_int8_t af);
> extern void xt_compat_unlock(u_int8_t af);
>
> -extern int xt_compat_add_offset(u_int8_t af, unsigned int offset, short delta);
> +extern int xt_compat_add_offset(u_int8_t af, unsigned int offset, int delta);
> extern void xt_compat_flush_offsets(u_int8_t af);
> +extern void xt_compat_init_offsets(u_int8_t af, unsigned int number);
> extern int xt_compat_calc_jump(u_int8_t af, unsigned int offset);
>
> extern int xt_compat_match_offset(const struct xt_match *match);
> diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
> index cbc9f39..2bf2fb2 100644
> --- a/net/bridge/netfilter/ebtables.c
> +++ b/net/bridge/netfilter/ebtables.c
> @@ -1764,6 +1764,7 @@ static int compat_table_info(const struct ebt_table_info *info,
>
> newinfo->entries_size = size;
>
> + xt_compat_init_offsets(AF_INET, info->nentries);
> return EBT_ENTRY_ITERATE(entries, size, compat_calc_entry, info,
> entries, newinfo);
> }
> diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
> index 3fac340..47e5178 100644
> --- a/net/ipv4/netfilter/arp_tables.c
> +++ b/net/ipv4/netfilter/arp_tables.c
> @@ -883,6 +883,7 @@ static int compat_table_info(const struct xt_table_info *info,
> memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
> newinfo->initial_entries = 0;
> loc_cpu_entry = info->entries[raw_smp_processor_id()];
> + xt_compat_init_offsets(NFPROTO_ARP, info->number);
> xt_entry_foreach(iter, loc_cpu_entry, info->size) {
> ret = compat_calc_entry(iter, info, loc_cpu_entry, newinfo);
> if (ret != 0)
> @@ -1350,6 +1351,7 @@ static int translate_compat_table(const char *name,
> duprintf("translate_compat_table: size %u\n", info->size);
> j = 0;
> xt_compat_lock(NFPROTO_ARP);
> + xt_compat_init_offsets(NFPROTO_ARP, number);
> /* Walk through entries, checking offsets. */
> xt_entry_foreach(iter0, entry0, total_size) {
> ret = check_compat_entry_size_and_hooks(iter0, info, &size,
> diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
> index a846d63..c5a75d7 100644
> --- a/net/ipv4/netfilter/ip_tables.c
> +++ b/net/ipv4/netfilter/ip_tables.c
> @@ -1080,6 +1080,7 @@ static int compat_table_info(const struct xt_table_info *info,
> memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
> newinfo->initial_entries = 0;
> loc_cpu_entry = info->entries[raw_smp_processor_id()];
> + xt_compat_init_offsets(AF_INET, info->number);
> xt_entry_foreach(iter, loc_cpu_entry, info->size) {
> ret = compat_calc_entry(iter, info, loc_cpu_entry, newinfo);
> if (ret != 0)
> @@ -1681,6 +1682,7 @@ translate_compat_table(struct net *net,
> duprintf("translate_compat_table: size %u\n", info->size);
> j = 0;
> xt_compat_lock(AF_INET);
> + xt_compat_init_offsets(AF_INET, number);
> /* Walk through entries, checking offsets. */
> xt_entry_foreach(iter0, entry0, total_size) {
> ret = check_compat_entry_size_and_hooks(iter0, info, &size,
> diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
> index 4555823..0c9973a 100644
> --- a/net/ipv6/netfilter/ip6_tables.c
> +++ b/net/ipv6/netfilter/ip6_tables.c
> @@ -1093,6 +1093,7 @@ static int compat_table_info(const struct xt_table_info *info,
> memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
> newinfo->initial_entries = 0;
> loc_cpu_entry = info->entries[raw_smp_processor_id()];
> + xt_compat_init_offsets(AF_INET6, info->number);
> xt_entry_foreach(iter, loc_cpu_entry, info->size) {
> ret = compat_calc_entry(iter, info, loc_cpu_entry, newinfo);
> if (ret != 0)
> @@ -1696,6 +1697,7 @@ translate_compat_table(struct net *net,
> duprintf("translate_compat_table: size %u\n", info->size);
> j = 0;
> xt_compat_lock(AF_INET6);
> + xt_compat_init_offsets(AF_INET6, number);
> /* Walk through entries, checking offsets. */
> xt_entry_foreach(iter0, entry0, total_size) {
> ret = check_compat_entry_size_and_hooks(iter0, info, &size,
> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> index 8046350..75182ed 100644
> --- a/net/netfilter/x_tables.c
> +++ b/net/netfilter/x_tables.c
> @@ -38,9 +38,8 @@ MODULE_DESCRIPTION("{ip,ip6,arp,eb}_tables backend module");
> #define SMP_ALIGN(x) (((x) + SMP_CACHE_BYTES-1) & ~(SMP_CACHE_BYTES-1))
>
> struct compat_delta {
> - struct compat_delta *next;
> - unsigned int offset;
> - int delta;
> + unsigned int offset; /* offset in kernel */
> + int delta; /* delta in 32bit user land */
> };
>
> struct xt_af {
> @@ -49,7 +48,9 @@ struct xt_af {
> struct list_head target;
> #ifdef CONFIG_COMPAT
> struct mutex compat_mutex;
> - struct compat_delta *compat_offsets;
> + struct compat_delta *compat_tab;
> + unsigned int number; /* number of slots in compat_tab[] */
> + unsigned int cur; /* number of used slots in compat_tab[] */
> #endif
> };
>
> @@ -414,54 +415,67 @@ int xt_check_match(struct xt_mtchk_param *par,
> EXPORT_SYMBOL_GPL(xt_check_match);
>
> #ifdef CONFIG_COMPAT
> -int xt_compat_add_offset(u_int8_t af, unsigned int offset, short delta)
> +int xt_compat_add_offset(u_int8_t af, unsigned int offset, int delta)
> {
> - struct compat_delta *tmp;
> + struct xt_af *xp = &xt[af];
>
> - tmp = kmalloc(sizeof(struct compat_delta), GFP_KERNEL);
> - if (!tmp)
> - return -ENOMEM;
> + if (!xp->compat_tab) {
> + if (!xp->number)
> + return -EINVAL;
> + xp->compat_tab = vmalloc(sizeof(struct compat_delta) * xp->number);
> + if (!xp->compat_tab)
> + return -ENOMEM;
> + xp->cur = 0;
> + }
>
> - tmp->offset = offset;
> - tmp->delta = delta;
> + if (xp->cur >= xp->number)
> + return -EINVAL;

minor glitch: We leak xp->compat_tab if this error condition above is true.

>
> - if (xt[af].compat_offsets) {
> - tmp->next = xt[af].compat_offsets->next;
> - xt[af].compat_offsets->next = tmp;
> - } else {
> - xt[af].compat_offsets = tmp;
> - tmp->next = NULL;
> - }
> + if (xp->cur)
> + delta += xp->compat_tab[xp->cur - 1].delta;
> + xp->compat_tab[xp->cur].offset = offset;
> + xp->compat_tab[xp->cur].delta = delta;
> + xp->cur++;
> return 0;
> }
> EXPORT_SYMBOL_GPL(xt_compat_add_offset);
>
> void xt_compat_flush_offsets(u_int8_t af)
> {
> - struct compat_delta *tmp, *next;
> -
> - if (xt[af].compat_offsets) {
> - for (tmp = xt[af].compat_offsets; tmp; tmp = next) {
> - next = tmp->next;
> - kfree(tmp);
> - }
> - xt[af].compat_offsets = NULL;
> + if (xt[af].compat_tab) {
> + vfree(xt[af].compat_tab);
> + xt[af].compat_tab = NULL;
> + xt[af].number = 0;
> }
> }
> EXPORT_SYMBOL_GPL(xt_compat_flush_offsets);
>
> int xt_compat_calc_jump(u_int8_t af, unsigned int offset)
> {
> - struct compat_delta *tmp;
> - int delta;
> -
> - for (tmp = xt[af].compat_offsets, delta = 0; tmp; tmp = tmp->next)
> - if (tmp->offset < offset)
> - delta += tmp->delta;
> - return delta;
> + struct compat_delta *tmp = xt[af].compat_tab;
> + int mid, left = 0, right = xt[af].cur - 1;
> +
> + while (left <= right) {
> + mid = (left + right) >> 1;
> + if (offset > tmp[mid].offset)
> + left = mid + 1;
> + else if (offset < tmp[mid].offset)
> + right = mid - 1;
> + else
> + return mid ? tmp[mid - 1].delta : 0;
> + }
> + WARN_ON_ONCE(1);
> + return 0;
> }
> EXPORT_SYMBOL_GPL(xt_compat_calc_jump);
>
> +void xt_compat_init_offsets(u_int8_t af, unsigned int number)
> +{
> + xt[af].number = number;
> + xt[af].cur = 0;
> +}
> +EXPORT_SYMBOL(xt_compat_init_offsets);
> +
> int xt_compat_match_offset(const struct xt_match *match)
> {
> u_int16_t csize = match->compatsize ? : match->matchsize;
> @@ -1337,7 +1351,7 @@ static int __init xt_init(void)
> mutex_init(&xt[i].mutex);
> #ifdef CONFIG_COMPAT
> mutex_init(&xt[i].compat_mutex);
> - xt[i].compat_offsets = NULL;
> + xt[i].compat_tab = NULL;
> #endif
> INIT_LIST_HEAD(&xt[i].target);
> INIT_LIST_HEAD(&xt[i].match);
>
>
> --
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