netfilter: get rid of atomic ops in fast path

extern struct xt_table_info *xt_alloc_table_info(unsigned int size);

extern void xt_free_table_info(struct xt_table_info *info);

/*

 * Per-CPU spinlock associated with per-cpu table entries, and

 * with a counter for the "reading" side that allows a recursive

 * reader to avoid taking the lock and deadlocking.

 *

 * "reading" is used by ip/arp/ip6 tables rule processing which runs per-cpu.

 * It needs to ensure that the rules are not being changed while the packet

 * is being processed. In some cases, the read lock will be acquired

 * twice on the same CPU; this is okay because of the count.

/**

 * xt_recseq - recursive seqcount for netfilter use

 * 

 * "writing" is used when reading counters.

 *  During replace any readers that are using the old tables have to complete

 *  before freeing the old table. This is handled by the write locking

 *  necessary for reading the counters.

 * Packet processing changes the seqcount only if no recursion happened

 * get_counters() can use read_seqcount_begin()/read_seqcount_retry(),

 * because we use the normal seqcount convention :

 * Low order bit set to 1 if a writer is active.

 */

struct xt_info_lock {

	seqlock_t lock;

	unsigned char readers;

};

DECLARE_PER_CPU(struct xt_info_lock, xt_info_locks);

DECLARE_PER_CPU(seqcount_t, xt_recseq);

/*

 * Note: we need to ensure that preemption is disabled before acquiring

 * the per-cpu-variable, so we do it as a two step process rather than

 * using "spin_lock_bh()".

 *

 * We _also_ need to disable bottom half processing before updating our

 * nesting count, to make sure that the only kind of re-entrancy is this

 * code being called by itself: since the count+lock is not an atomic

 * operation, we can allow no races.

/**

 * xt_write_recseq_begin - start of a write section

 *

 * _Only_ that special combination of being per-cpu and never getting

 * re-entered asynchronously means that the count is safe.

 * Begin packet processing : all readers must wait the end

 * 1) Must be called with preemption disabled

 * 2) softirqs must be disabled too (or we should use irqsafe_cpu_add())

 * Returns :

 *  1 if no recursion on this cpu

 *  0 if recursion detected

 */

static inline void xt_info_rdlock_bh(void)

static inline unsigned int xt_write_recseq_begin(void)

{

	struct xt_info_lock *lock;

	unsigned int addend;

	local_bh_disable();

	lock = &__get_cpu_var(xt_info_locks);

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

		write_seqlock(&lock->lock);

}

static inline void xt_info_rdunlock_bh(void)

{

	struct xt_info_lock *lock = &__get_cpu_var(xt_info_locks);

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

		write_sequnlock(&lock->lock);

	local_bh_enable();

}

	/*

	 * Low order bit of sequence is set if we already

	 * called xt_write_recseq_begin().

	 */

	addend = (__this_cpu_read(xt_recseq.sequence) + 1) & 1;

	/*

 * The "writer" side needs to get exclusive access to the lock,

 * regardless of readers.  This must be called with bottom half

 * processing (and thus also preemption) disabled.

	 * This is kind of a write_seqcount_begin(), but addend is 0 or 1

	 * We dont check addend value to avoid a test and conditional jump,

	 * since addend is most likely 1

	 */

static inline void xt_info_wrlock(unsigned int cpu)

{

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

	__this_cpu_add(xt_recseq.sequence, addend);

	smp_wmb();

	return addend;

}

static inline void xt_info_wrunlock(unsigned int cpu)

/**

 * xt_write_recseq_end - end of a write section

 * @addend: return value from previous xt_write_recseq_begin()

 *

 * End packet processing : all readers can proceed

 * 1) Must be called with preemption disabled

 * 2) softirqs must be disabled too (or we should use irqsafe_cpu_add())

 */

static inline void xt_write_recseq_end(unsigned int addend)

{

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

	/* this is kind of a write_seqcount_end(), but addend is 0 or 1 */

	smp_wmb();

	__this_cpu_add(xt_recseq.sequence, addend);

}

/*

	void *table_base;

	const struct xt_table_info *private;

	struct xt_action_param acpar;

	unsigned int addend;

	if (!pskb_may_pull(skb, arp_hdr_len(skb->dev)))

		return NF_DROP;

	indev = in ? in->name : nulldevname;

	outdev = out ? out->name : nulldevname;

	xt_info_rdlock_bh();

	local_bh_disable();

	addend = xt_write_recseq_begin();

	private = table->private;

	table_base = private->entries[smp_processor_id()];

			/* Verdict */

			break;

	} while (!acpar.hotdrop);

	xt_info_rdunlock_bh();

	xt_write_recseq_end(addend);

	local_bh_enable();

	if (acpar.hotdrop)

		return NF_DROP;

	unsigned int i;

	for_each_possible_cpu(cpu) {

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

		seqcount_t *s = &per_cpu(xt_recseq, cpu);

		i = 0;

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

			unsigned int start;

			do {

				start = read_seqbegin(lock);

				start = read_seqcount_begin(s);

				bcnt = iter->counters.bcnt;

				pcnt = iter->counters.pcnt;

			} while (read_seqretry(lock, start));

			} while (read_seqcount_retry(s, start));

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

			++i;

	int ret = 0;

	void *loc_cpu_entry;

	struct arpt_entry *iter;

	unsigned int addend;

#ifdef CONFIG_COMPAT

	struct compat_xt_counters_info compat_tmp;

	/* Choose the copy that is on our node */

	curcpu = smp_processor_id();

	loc_cpu_entry = private->entries[curcpu];

	xt_info_wrlock(curcpu);

	addend = xt_write_recseq_begin();

	xt_entry_foreach(iter, loc_cpu_entry, private->size) {

		ADD_COUNTER(iter->counters, paddc[i].bcnt, paddc[i].pcnt);

		++i;

	}

	xt_info_wrunlock(curcpu);

	xt_write_recseq_end(addend);

 unlock_up_free:

	local_bh_enable();

	xt_table_unlock(t);

}

EXPORT_SYMBOL_GPL(ipt_alloc_initial_table);

/*

   We keep a set of rules for each CPU, so we can avoid write-locking

   them in the softirq when updating the counters and therefore

   only need to read-lock in the softirq; doing a write_lock_bh() in user

   context stops packets coming through and allows user context to read

   the counters or update the rules.

   Hence the start of any table is given by get_table() below.  */

/* Returns whether matches rule or not. */

/* Performance critical - called for every packet */

static inline bool

	unsigned int *stackptr, origptr, cpu;

	const struct xt_table_info *private;

	struct xt_action_param acpar;

	unsigned int addend;

	/* Initialization */

	ip = ip_hdr(skb);

	acpar.hooknum = hook;

	IP_NF_ASSERT(table->valid_hooks & (1 << hook));

	xt_info_rdlock_bh();

	local_bh_disable();

	addend = xt_write_recseq_begin();

	private = table->private;

	cpu        = smp_processor_id();

	table_base = private->entries[cpu];

	pr_debug("Exiting %s; resetting sp from %u to %u\n",

		 __func__, *stackptr, origptr);

	*stackptr = origptr;

	xt_info_rdunlock_bh();

 	xt_write_recseq_end(addend);

 	local_bh_enable();

#ifdef DEBUG_ALLOW_ALL

	return NF_ACCEPT;

#else

	unsigned int i;

	for_each_possible_cpu(cpu) {

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

		seqcount_t *s = &per_cpu(xt_recseq, cpu);

		i = 0;

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

			unsigned int start;

			do {

				start = read_seqbegin(lock);

				start = read_seqcount_begin(s);

				bcnt = iter->counters.bcnt;

				pcnt = iter->counters.pcnt;

			} while (read_seqretry(lock, start));

			} while (read_seqcount_retry(s, start));

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

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

	int ret = 0;

	void *loc_cpu_entry;

	struct ipt_entry *iter;

	unsigned int addend;

#ifdef CONFIG_COMPAT

	struct compat_xt_counters_info compat_tmp;

	/* Choose the copy that is on our node */

	curcpu = smp_processor_id();

	loc_cpu_entry = private->entries[curcpu];

	xt_info_wrlock(curcpu);

	addend = xt_write_recseq_begin();

	xt_entry_foreach(iter, loc_cpu_entry, private->size) {

		ADD_COUNTER(iter->counters, paddc[i].bcnt, paddc[i].pcnt);

		++i;

	}

	xt_info_wrunlock(curcpu);

	xt_write_recseq_end(addend);

 unlock_up_free:

	local_bh_enable();

	xt_table_unlock(t);

	unsigned int *stackptr, origptr, cpu;

	const struct xt_table_info *private;

	struct xt_action_param acpar;

	unsigned int addend;

	/* Initialization */

	indev = in ? in->name : nulldevname;

	IP_NF_ASSERT(table->valid_hooks & (1 << hook));

	xt_info_rdlock_bh();

	local_bh_disable();

	addend = xt_write_recseq_begin();

	private = table->private;

	cpu        = smp_processor_id();

	table_base = private->entries[cpu];

	} while (!acpar.hotdrop);

	*stackptr = origptr;

	xt_info_rdunlock_bh();

 	xt_write_recseq_end(addend);

 	local_bh_enable();

#ifdef DEBUG_ALLOW_ALL

	return NF_ACCEPT;

	unsigned int i;

	for_each_possible_cpu(cpu) {

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

		seqcount_t *s = &per_cpu(xt_recseq, cpu);

		i = 0;

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

			unsigned int start;

			do {

				start = read_seqbegin(lock);

				start = read_seqcount_begin(s);

				bcnt = iter->counters.bcnt;

				pcnt = iter->counters.pcnt;

			} while (read_seqretry(lock, start));

			} while (read_seqcount_retry(s, start));

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

			++i;

	int ret = 0;

	const void *loc_cpu_entry;

	struct ip6t_entry *iter;

	unsigned int addend;

#ifdef CONFIG_COMPAT

	struct compat_xt_counters_info compat_tmp;

	i = 0;

	/* Choose the copy that is on our node */

	curcpu = smp_processor_id();

	xt_info_wrlock(curcpu);

	addend = xt_write_recseq_begin();

	loc_cpu_entry = private->entries[curcpu];

	xt_entry_foreach(iter, loc_cpu_entry, private->size) {

		ADD_COUNTER(iter->counters, paddc[i].bcnt, paddc[i].pcnt);

		++i;

	}

	xt_info_wrunlock(curcpu);

	xt_write_recseq_end(addend);

 unlock_up_free:

	local_bh_enable();

EXPORT_SYMBOL_GPL(xt_compat_unlock);

#endif

DEFINE_PER_CPU(struct xt_info_lock, xt_info_locks);

EXPORT_PER_CPU_SYMBOL_GPL(xt_info_locks);

DEFINE_PER_CPU(seqcount_t, xt_recseq);

EXPORT_PER_CPU_SYMBOL_GPL(xt_recseq);

static int xt_jumpstack_alloc(struct xt_table_info *i)

{

	int rv;

	for_each_possible_cpu(i) {

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

		seqlock_init(&lock->lock);

		lock->readers = 0;

		seqcount_init(&per_cpu(xt_recseq, i));

	}

	xt = kmalloc(sizeof(struct xt_af) * NFPROTO_NUMPROTO, GFP_KERNEL);