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Commit 83723d60 authored by Eric Dumazet's avatar Eric Dumazet Committed by Pablo Neira Ayuso
Browse files

netfilter: x_tables: dont block BH while reading counters 



Using "iptables -L" with a lot of rules have a too big BH latency.
Jesper mentioned ~6 ms and worried of frame drops.

Switch to a per_cpu seqlock scheme, so that taking a snapshot of
counters doesnt need to block BH (for this cpu, but also other cpus).

This adds two increments on seqlock sequence per ipt_do_table() call,
its a reasonable cost for allowing "iptables -L" not block BH
processing.

Reported-by: default avatarJesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
Acked-by: default avatarStephen Hemminger <shemminger@vyatta.com>
Acked-by: default avatarJesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent 45b9f509

include/linux/netfilter/x_tables.h

+5 −5
Original line number Diff line number Diff line
@@ -472,7 +472,7 @@ extern void xt_free_table_info(struct xt_table_info *info); 
 *  necessary for reading the counters.

 */

struct xt_info_lock {

	spinlock_t lock;

	seqlock_t lock;

	unsigned char readers;

};

DECLARE_PER_CPU(struct xt_info_lock, xt_info_locks);
@@ -497,7 +497,7 @@ static inline void xt_info_rdlock_bh(void) 
	local_bh_disable();

	lock = &__get_cpu_var(xt_info_locks);

	if (likely(!lock->readers++))

		spin_lock(&lock->lock);

		write_seqlock(&lock->lock);

}



static inline void xt_info_rdunlock_bh(void)
@@ -505,7 +505,7 @@ static inline void xt_info_rdunlock_bh(void) 
	struct xt_info_lock *lock = &__get_cpu_var(xt_info_locks);



	if (likely(!--lock->readers))

		spin_unlock(&lock->lock);

		write_sequnlock(&lock->lock);

	local_bh_enable();

}
@@ -516,12 +516,12 @@ static inline void xt_info_rdunlock_bh(void) 
 */

static inline void xt_info_wrlock(unsigned int cpu)

{

	spin_lock(&per_cpu(xt_info_locks, cpu).lock);

	write_seqlock(&per_cpu(xt_info_locks, cpu).lock);

}



static inline void xt_info_wrunlock(unsigned int cpu)

{

	spin_unlock(&per_cpu(xt_info_locks, cpu).lock);

	write_sequnlock(&per_cpu(xt_info_locks, cpu).lock);

}



/*

net/ipv4/netfilter/arp_tables.c

+14 −31
Original line number Diff line number Diff line
@@ -710,42 +710,25 @@ static void get_counters(const struct xt_table_info *t, 
	struct arpt_entry *iter;

	unsigned int cpu;

	unsigned int i;

	unsigned int curcpu = get_cpu();



	/* Instead of clearing (by a previous call to memset())

	 * the counters and using adds, we set the counters

	 * 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

	 */

	local_bh_disable();

	i = 0;

	xt_entry_foreach(iter, t->entries[curcpu], t->size) {

		SET_COUNTER(counters[i], iter->counters.bcnt,

			    iter->counters.pcnt);

		++i;

	}

	local_bh_enable();

	/* Processing counters from other cpus, we can let bottom half enabled,

	 * (preemption is disabled)

	 */



	for_each_possible_cpu(cpu) {

		if (cpu == curcpu)

			continue;

		seqlock_t *lock = &per_cpu(xt_info_locks, cpu).lock;



		i = 0;

		local_bh_disable();

		xt_info_wrlock(cpu);

		xt_entry_foreach(iter, t->entries[cpu], t->size) {

			ADD_COUNTER(counters[i], iter->counters.bcnt,

				    iter->counters.pcnt);

			u64 bcnt, pcnt;

			unsigned int start;



			do {

				start = read_seqbegin(lock);

				bcnt = iter->counters.bcnt;

				pcnt = iter->counters.pcnt;

			} while (read_seqretry(lock, start));



			ADD_COUNTER(counters[i], bcnt, pcnt);

			++i;

		}

		xt_info_wrunlock(cpu);

		local_bh_enable();

	}

	put_cpu();

}



static struct xt_counters *alloc_counters(const struct xt_table *table)
@@ -759,7 +742,7 @@ static struct xt_counters *alloc_counters(const struct xt_table *table) 
	 * about).

	 */

	countersize = sizeof(struct xt_counters) * private->number;

	counters = vmalloc(countersize);

	counters = vzalloc(countersize);



	if (counters == NULL)

		return ERR_PTR(-ENOMEM);
@@ -1007,7 +990,7 @@ static int __do_replace(struct net *net, const char *name, 
	struct arpt_entry *iter;



	ret = 0;

	counters = vmalloc(num_counters * sizeof(struct xt_counters));

	counters = vzalloc(num_counters * sizeof(struct xt_counters));

	if (!counters) {

		ret = -ENOMEM;

		goto out;

net/ipv4/netfilter/ip_tables.c

+14 −31
Original line number Diff line number Diff line
@@ -884,42 +884,25 @@ get_counters(const struct xt_table_info *t, 
	struct ipt_entry *iter;

	unsigned int cpu;

	unsigned int i;

	unsigned int curcpu = get_cpu();



	/* Instead of clearing (by a previous call to memset())

	 * the counters and using adds, we set the counters

	 * 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

	 */

	local_bh_disable();

	i = 0;

	xt_entry_foreach(iter, t->entries[curcpu], t->size) {

		SET_COUNTER(counters[i], iter->counters.bcnt,

			    iter->counters.pcnt);

		++i;

	}

	local_bh_enable();

	/* Processing counters from other cpus, we can let bottom half enabled,

	 * (preemption is disabled)

	 */



	for_each_possible_cpu(cpu) {

		if (cpu == curcpu)

			continue;

		seqlock_t *lock = &per_cpu(xt_info_locks, cpu).lock;



		i = 0;

		local_bh_disable();

		xt_info_wrlock(cpu);

		xt_entry_foreach(iter, t->entries[cpu], t->size) {

			ADD_COUNTER(counters[i], iter->counters.bcnt,

				    iter->counters.pcnt);

			u64 bcnt, pcnt;

			unsigned int start;



			do {

				start = read_seqbegin(lock);

				bcnt = iter->counters.bcnt;

				pcnt = iter->counters.pcnt;

			} while (read_seqretry(lock, start));



			ADD_COUNTER(counters[i], bcnt, pcnt);

			++i; /* macro does multi eval of i */

		}

		xt_info_wrunlock(cpu);

		local_bh_enable();

	}

	put_cpu();

}



static struct xt_counters *alloc_counters(const struct xt_table *table)
@@ -932,7 +915,7 @@ static struct xt_counters *alloc_counters(const struct xt_table *table) 
	   (other than comefrom, which userspace doesn't care

	   about). */

	countersize = sizeof(struct xt_counters) * private->number;

	counters = vmalloc(countersize);

	counters = vzalloc(countersize);



	if (counters == NULL)

		return ERR_PTR(-ENOMEM);
@@ -1203,7 +1186,7 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks, 
	struct ipt_entry *iter;



	ret = 0;

	counters = vmalloc(num_counters * sizeof(struct xt_counters));

	counters = vzalloc(num_counters * sizeof(struct xt_counters));

	if (!counters) {

		ret = -ENOMEM;

		goto out;

net/ipv6/netfilter/ip6_tables.c

+14 −31
Original line number Diff line number Diff line
@@ -897,42 +897,25 @@ get_counters(const struct xt_table_info *t, 
	struct ip6t_entry *iter;

	unsigned int cpu;

	unsigned int i;

	unsigned int curcpu = get_cpu();



	/* Instead of clearing (by a previous call to memset())

	 * the counters and using adds, we set the counters

	 * 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

	 */

	local_bh_disable();

	i = 0;

	xt_entry_foreach(iter, t->entries[curcpu], t->size) {

		SET_COUNTER(counters[i], iter->counters.bcnt,

			    iter->counters.pcnt);

		++i;

	}

	local_bh_enable();

	/* Processing counters from other cpus, we can let bottom half enabled,

	 * (preemption is disabled)

	 */



	for_each_possible_cpu(cpu) {

		if (cpu == curcpu)

			continue;

		seqlock_t *lock = &per_cpu(xt_info_locks, cpu).lock;



		i = 0;

		local_bh_disable();

		xt_info_wrlock(cpu);

		xt_entry_foreach(iter, t->entries[cpu], t->size) {

			ADD_COUNTER(counters[i], iter->counters.bcnt,

				    iter->counters.pcnt);

			u64 bcnt, pcnt;

			unsigned int start;



			do {

				start = read_seqbegin(lock);

				bcnt = iter->counters.bcnt;

				pcnt = iter->counters.pcnt;

			} while (read_seqretry(lock, start));



			ADD_COUNTER(counters[i], bcnt, pcnt);

			++i;

		}

		xt_info_wrunlock(cpu);

		local_bh_enable();

	}

	put_cpu();

}



static struct xt_counters *alloc_counters(const struct xt_table *table)
@@ -945,7 +928,7 @@ static struct xt_counters *alloc_counters(const struct xt_table *table) 
	   (other than comefrom, which userspace doesn't care

	   about). */

	countersize = sizeof(struct xt_counters) * private->number;

	counters = vmalloc(countersize);

	counters = vzalloc(countersize);



	if (counters == NULL)

		return ERR_PTR(-ENOMEM);
@@ -1216,7 +1199,7 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks, 
	struct ip6t_entry *iter;



	ret = 0;

	counters = vmalloc(num_counters * sizeof(struct xt_counters));

	counters = vzalloc(num_counters * sizeof(struct xt_counters));

	if (!counters) {

		ret = -ENOMEM;

		goto out;

net/netfilter/x_tables.c

+2 −1
Original line number Diff line number Diff line
@@ -1325,7 +1325,8 @@ static int __init xt_init(void) 


	for_each_possible_cpu(i) {

		struct xt_info_lock *lock = &per_cpu(xt_info_locks, i);

		spin_lock_init(&lock->lock);



		seqlock_init(&lock->lock);

		lock->readers = 0;

	}