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Commit b145425f authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

inetpeer: remove AVL implementation in favor of RB tree 



As discussed in Faro during Netfilter Workshop 2017, RB trees can be
used with RCU, using a seqlock.

Note that net/rxrpc/conn_service.c is already using this.

This patch converts inetpeer from AVL tree to RB tree, since it allows
to remove private AVL implementation in favor of shared RB code.

$ size net/ipv4/inetpeer.before net/ipv4/inetpeer.after
   text    data     bss     dec     hex filename
   3195      40     128    3363     d23 net/ipv4/inetpeer.before
   1562      24       0    1586     632 net/ipv4/inetpeer.after

The same technique can be used to speed up
net/netfilter/nft_set_rbtree.c (removing rwlock contention in fast path)

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 27eac47b

include/net/inetpeer.h

+2 −9
Original line number Diff line number Diff line
@@ -33,18 +33,12 @@ struct inetpeer_addr { 
};



struct inet_peer {

	/* group together avl_left,avl_right,v4daddr to speedup lookups */

	struct inet_peer __rcu	*avl_left, *avl_right;

	struct rb_node		rb_node;

	struct inetpeer_addr	daddr;

	__u32			avl_height;



	u32			metrics[RTAX_MAX];

	u32			rate_tokens;	/* rate limiting for ICMP */

	unsigned long		rate_last;

	union {

		struct list_head	gc_list;

		struct rcu_head     gc_rcu;

	};

	/*

	 * Once inet_peer is queued for deletion (refcnt == 0), following field

	 * is not available: rid
@@ -55,7 +49,6 @@ struct inet_peer { 
			atomic_t			rid;		/* Frag reception counter */

		};

		struct rcu_head         rcu;

		struct inet_peer	*gc_next;

	};



	/* following fields might be frequently dirtied */
@@ -64,7 +57,7 @@ struct inet_peer { 
};



struct inet_peer_base {

	struct inet_peer __rcu	*root;

	struct rb_root		rb_root;

	seqlock_t		lock;

	int			total;

};

net/ipv4/inetpeer.c

+90 −338
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ 
 *  also be removed if the pool is overloaded i.e. if the total amount of

 *  entries is greater-or-equal than the threshold.

 *

 *  Node pool is organised as an AVL tree.

 *  Node pool is organised as an RB tree.

 *  Such an implementation has been chosen not just for fun.  It's a way to

 *  prevent easy and efficient DoS attacks by creating hash collisions.  A huge

 *  amount of long living nodes in a single hash slot would significantly delay
@@ -45,7 +45,7 @@ 
 *      AND reference count being 0.

 *  3.  Global variable peer_total is modified under the pool lock.

 *  4.  struct inet_peer fields modification:

 *		avl_left, avl_right, avl_parent, avl_height: pool lock

 *		rb_node: pool lock

 *		refcnt: atomically against modifications on other CPU;

 *		   usually under some other lock to prevent node disappearing

 *		daddr: unchangeable
@@ -53,30 +53,15 @@ 


static struct kmem_cache *peer_cachep __read_mostly;



static LIST_HEAD(gc_list);

static const int gc_delay = 60 * HZ;

static struct delayed_work gc_work;

static DEFINE_SPINLOCK(gc_lock);



#define node_height(x) x->avl_height



#define peer_avl_empty ((struct inet_peer *)&peer_fake_node)

#define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node)

static const struct inet_peer peer_fake_node = {

	.avl_left	= peer_avl_empty_rcu,

	.avl_right	= peer_avl_empty_rcu,

	.avl_height	= 0

};



void inet_peer_base_init(struct inet_peer_base *bp)

{

	bp->root = peer_avl_empty_rcu;

	bp->rb_root = RB_ROOT;

	seqlock_init(&bp->lock);

	bp->total = 0;

}

EXPORT_SYMBOL_GPL(inet_peer_base_init);



#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */

#define PEER_MAX_GC 32



/* Exported for sysctl_net_ipv4.  */

int inet_peer_threshold __read_mostly = 65536 + 128;	/* start to throw entries more
@@ -84,53 +69,6 @@ int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries m 
int inet_peer_minttl __read_mostly = 120 * HZ;	/* TTL under high load: 120 sec */

int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;	/* usual time to live: 10 min */



static void inetpeer_gc_worker(struct work_struct *work)

{

	struct inet_peer *p, *n, *c;

	struct list_head list;



	spin_lock_bh(&gc_lock);

	list_replace_init(&gc_list, &list);

	spin_unlock_bh(&gc_lock);



	if (list_empty(&list))

		return;



	list_for_each_entry_safe(p, n, &list, gc_list) {



		if (need_resched())

			cond_resched();



		c = rcu_dereference_protected(p->avl_left, 1);

		if (c != peer_avl_empty) {

			list_add_tail(&c->gc_list, &list);

			p->avl_left = peer_avl_empty_rcu;

		}



		c = rcu_dereference_protected(p->avl_right, 1);

		if (c != peer_avl_empty) {

			list_add_tail(&c->gc_list, &list);

			p->avl_right = peer_avl_empty_rcu;

		}



		n = list_entry(p->gc_list.next, struct inet_peer, gc_list);



		if (refcount_read(&p->refcnt) == 1) {

			list_del(&p->gc_list);

			kmem_cache_free(peer_cachep, p);

		}

	}



	if (list_empty(&list))

		return;



	spin_lock_bh(&gc_lock);

	list_splice(&list, &gc_list);

	spin_unlock_bh(&gc_lock);



	schedule_delayed_work(&gc_work, gc_delay);

}



/* Called from ip_output.c:ip_init  */

void __init inet_initpeers(void)

{
@@ -153,225 +91,62 @@ void __init inet_initpeers(void) 
			sizeof(struct inet_peer),

			0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,

			NULL);



	INIT_DEFERRABLE_WORK(&gc_work, inetpeer_gc_worker);

}



#define rcu_deref_locked(X, BASE)				\

	rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock))



/*

 * Called with local BH disabled and the pool lock held.

 */

#define lookup(_daddr, _stack, _base)				\

({								\

	struct inet_peer *u;					\

	struct inet_peer __rcu **v;				\

								\

	stackptr = _stack;					\

	*stackptr++ = &_base->root;				\

	for (u = rcu_deref_locked(_base->root, _base);		\

	     u != peer_avl_empty;) {				\

		int cmp = inetpeer_addr_cmp(_daddr, &u->daddr);	\

		if (cmp == 0)					\

			break;					\

		if (cmp == -1)					\

			v = &u->avl_left;			\

		else						\

			v = &u->avl_right;			\

		*stackptr++ = v;				\

		u = rcu_deref_locked(*v, _base);		\

	}							\

	u;							\

})



/*

 * Called with rcu_read_lock()

 * Because we hold no lock against a writer, its quite possible we fall

 * in an endless loop.

 * But every pointer we follow is guaranteed to be valid thanks to RCU.

 * We exit from this function if number of links exceeds PEER_MAXDEPTH

 */

static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,

				    struct inet_peer_base *base)

/* Called with rcu_read_lock() or base->lock held */

static struct inet_peer *lookup(const struct inetpeer_addr *daddr,

				struct inet_peer_base *base,

				unsigned int seq,

				struct inet_peer *gc_stack[],

				unsigned int *gc_cnt,

				struct rb_node **parent_p,

				struct rb_node ***pp_p)

{

	struct inet_peer *u = rcu_dereference(base->root);

	int count = 0;

	struct rb_node **pp, *parent;

	struct inet_peer *p;



	while (u != peer_avl_empty) {

		int cmp = inetpeer_addr_cmp(daddr, &u->daddr);

	pp = &base->rb_root.rb_node;

	parent = NULL;

	while (*pp) {

		int cmp;



		parent = rcu_dereference_raw(*pp);

		p = rb_entry(parent, struct inet_peer, rb_node);

		cmp = inetpeer_addr_cmp(daddr, &p->daddr);

		if (cmp == 0) {

			/* Before taking a reference, check if this entry was

			 * deleted (refcnt=0)

			 */

			if (!refcount_inc_not_zero(&u->refcnt)) {

				u = NULL;

			if (!refcount_inc_not_zero(&p->refcnt))

				break;

			return p;

		}

			return u;

		if (gc_stack) {

			if (*gc_cnt < PEER_MAX_GC)

				gc_stack[(*gc_cnt)++] = p;

		} else if (unlikely(read_seqretry(&base->lock, seq))) {

			break;

		}

		if (cmp == -1)

			u = rcu_dereference(u->avl_left);

			pp = &(*pp)->rb_left;

		else

			u = rcu_dereference(u->avl_right);

		if (unlikely(++count == PEER_MAXDEPTH))

			break;

			pp = &(*pp)->rb_right;

	}

	*parent_p = parent;

	*pp_p = pp;

	return NULL;

}



/* Called with local BH disabled and the pool lock held. */

#define lookup_rightempty(start, base)				\

({								\

	struct inet_peer *u;					\

	struct inet_peer __rcu **v;				\

	*stackptr++ = &start->avl_left;				\

	v = &start->avl_left;					\

	for (u = rcu_deref_locked(*v, base);			\

	     u->avl_right != peer_avl_empty_rcu;) {		\

		v = &u->avl_right;				\

		*stackptr++ = v;				\

		u = rcu_deref_locked(*v, base);			\

	}							\

	u;							\

})



/* Called with local BH disabled and the pool lock held.

 * Variable names are the proof of operation correctness.

 * Look into mm/map_avl.c for more detail description of the ideas.

 */

static void peer_avl_rebalance(struct inet_peer __rcu **stack[],

			       struct inet_peer __rcu ***stackend,

			       struct inet_peer_base *base)

{

	struct inet_peer __rcu **nodep;

	struct inet_peer *node, *l, *r;

	int lh, rh;



	while (stackend > stack) {

		nodep = *--stackend;

		node = rcu_deref_locked(*nodep, base);

		l = rcu_deref_locked(node->avl_left, base);

		r = rcu_deref_locked(node->avl_right, base);

		lh = node_height(l);

		rh = node_height(r);

		if (lh > rh + 1) { /* l: RH+2 */

			struct inet_peer *ll, *lr, *lrl, *lrr;

			int lrh;

			ll = rcu_deref_locked(l->avl_left, base);

			lr = rcu_deref_locked(l->avl_right, base);

			lrh = node_height(lr);

			if (lrh <= node_height(ll)) {	/* ll: RH+1 */

				RCU_INIT_POINTER(node->avl_left, lr);	/* lr: RH or RH+1 */

				RCU_INIT_POINTER(node->avl_right, r);	/* r: RH */

				node->avl_height = lrh + 1; /* RH+1 or RH+2 */

				RCU_INIT_POINTER(l->avl_left, ll);       /* ll: RH+1 */

				RCU_INIT_POINTER(l->avl_right, node);	/* node: RH+1 or RH+2 */

				l->avl_height = node->avl_height + 1;

				RCU_INIT_POINTER(*nodep, l);

			} else { /* ll: RH, lr: RH+1 */

				lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */

				lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */

				RCU_INIT_POINTER(node->avl_left, lrr);	/* lrr: RH or RH-1 */

				RCU_INIT_POINTER(node->avl_right, r);	/* r: RH */

				node->avl_height = rh + 1; /* node: RH+1 */

				RCU_INIT_POINTER(l->avl_left, ll);	/* ll: RH */

				RCU_INIT_POINTER(l->avl_right, lrl);	/* lrl: RH or RH-1 */

				l->avl_height = rh + 1;	/* l: RH+1 */

				RCU_INIT_POINTER(lr->avl_left, l);	/* l: RH+1 */

				RCU_INIT_POINTER(lr->avl_right, node);	/* node: RH+1 */

				lr->avl_height = rh + 2;

				RCU_INIT_POINTER(*nodep, lr);

			}

		} else if (rh > lh + 1) { /* r: LH+2 */

			struct inet_peer *rr, *rl, *rlr, *rll;

			int rlh;

			rr = rcu_deref_locked(r->avl_right, base);

			rl = rcu_deref_locked(r->avl_left, base);

			rlh = node_height(rl);

			if (rlh <= node_height(rr)) {	/* rr: LH+1 */

				RCU_INIT_POINTER(node->avl_right, rl);	/* rl: LH or LH+1 */

				RCU_INIT_POINTER(node->avl_left, l);	/* l: LH */

				node->avl_height = rlh + 1; /* LH+1 or LH+2 */

				RCU_INIT_POINTER(r->avl_right, rr);	/* rr: LH+1 */

				RCU_INIT_POINTER(r->avl_left, node);	/* node: LH+1 or LH+2 */

				r->avl_height = node->avl_height + 1;

				RCU_INIT_POINTER(*nodep, r);

			} else { /* rr: RH, rl: RH+1 */

				rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */

				rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */

				RCU_INIT_POINTER(node->avl_right, rll);	/* rll: LH or LH-1 */

				RCU_INIT_POINTER(node->avl_left, l);	/* l: LH */

				node->avl_height = lh + 1; /* node: LH+1 */

				RCU_INIT_POINTER(r->avl_right, rr);	/* rr: LH */

				RCU_INIT_POINTER(r->avl_left, rlr);	/* rlr: LH or LH-1 */

				r->avl_height = lh + 1;	/* r: LH+1 */

				RCU_INIT_POINTER(rl->avl_right, r);	/* r: LH+1 */

				RCU_INIT_POINTER(rl->avl_left, node);	/* node: LH+1 */

				rl->avl_height = lh + 2;

				RCU_INIT_POINTER(*nodep, rl);

			}

		} else {

			node->avl_height = (lh > rh ? lh : rh) + 1;

		}

	}

}



/* Called with local BH disabled and the pool lock held. */

#define link_to_pool(n, base)					\

do {								\

	n->avl_height = 1;					\

	n->avl_left = peer_avl_empty_rcu;			\

	n->avl_right = peer_avl_empty_rcu;			\

	/* lockless readers can catch us now */			\

	rcu_assign_pointer(**--stackptr, n);			\

	peer_avl_rebalance(stack, stackptr, base);		\

} while (0)



static void inetpeer_free_rcu(struct rcu_head *head)

{

	kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));

}



static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,

			     struct inet_peer __rcu **stack[PEER_MAXDEPTH])

{

	struct inet_peer __rcu ***stackptr, ***delp;



	if (lookup(&p->daddr, stack, base) != p)

		BUG();

	delp = stackptr - 1; /* *delp[0] == p */

	if (p->avl_left == peer_avl_empty_rcu) {

		*delp[0] = p->avl_right;

		--stackptr;

	} else {

		/* look for a node to insert instead of p */

		struct inet_peer *t;

		t = lookup_rightempty(p, base);

		BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);

		**--stackptr = t->avl_left;

		/* t is removed, t->daddr > x->daddr for any

		 * x in p->avl_left subtree.

		 * Put t in the old place of p. */

		RCU_INIT_POINTER(*delp[0], t);

		t->avl_left = p->avl_left;

		t->avl_right = p->avl_right;

		t->avl_height = p->avl_height;

		BUG_ON(delp[1] != &p->avl_left);

		delp[1] = &t->avl_left; /* was &p->avl_left */

	}

	peer_avl_rebalance(stack, stackptr, base);

	base->total--;

	call_rcu(&p->rcu, inetpeer_free_rcu);

}



/* perform garbage collect on all items stacked during a lookup */

static int inet_peer_gc(struct inet_peer_base *base,

			struct inet_peer __rcu **stack[PEER_MAXDEPTH],

			struct inet_peer __rcu ***stackptr)

static void inet_peer_gc(struct inet_peer_base *base,

			 struct inet_peer *gc_stack[],

			 unsigned int gc_cnt)

{

	struct inet_peer *p, *gchead = NULL;

	struct inet_peer *p;

	__u32 delta, ttl;

	int cnt = 0;

	int i;



	if (base->total >= inet_peer_threshold)

		ttl = 0; /* be aggressive */
@@ -379,43 +154,38 @@ static int inet_peer_gc(struct inet_peer_base *base, 
		ttl = inet_peer_maxttl

				- (inet_peer_maxttl - inet_peer_minttl) / HZ *

					base->total / inet_peer_threshold * HZ;

	stackptr--; /* last stack slot is peer_avl_empty */

	while (stackptr > stack) {

		stackptr--;

		p = rcu_deref_locked(**stackptr, base);

		if (refcount_read(&p->refcnt) == 1) {

			smp_rmb();

	for (i = 0; i < gc_cnt; i++) {

		p = gc_stack[i];

		delta = (__u32)jiffies - p->dtime;

			if (delta >= ttl && refcount_dec_if_one(&p->refcnt)) {

				p->gc_next = gchead;

				gchead = p;

			}

		if (delta < ttl || !refcount_dec_if_one(&p->refcnt))

			gc_stack[i] = NULL;

	}

	for (i = 0; i < gc_cnt; i++) {

		p = gc_stack[i];

		if (p) {

			rb_erase(&p->rb_node, &base->rb_root);

			base->total--;

			call_rcu(&p->rcu, inetpeer_free_rcu);

		}

	while ((p = gchead) != NULL) {

		gchead = p->gc_next;

		cnt++;

		unlink_from_pool(p, base, stack);

	}

	return cnt;

}



struct inet_peer *inet_getpeer(struct inet_peer_base *base,

			       const struct inetpeer_addr *daddr,

			       int create)

{

	struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;

	struct inet_peer *p;

	unsigned int sequence;

	int invalidated, gccnt = 0;

	struct inet_peer *p, *gc_stack[PEER_MAX_GC];

	struct rb_node **pp, *parent;

	unsigned int gc_cnt, seq;

	int invalidated;



	/* Attempt a lockless lookup first.

	 * Because of a concurrent writer, we might not find an existing entry.

	 */

	rcu_read_lock();

	sequence = read_seqbegin(&base->lock);

	p = lookup_rcu(daddr, base);

	invalidated = read_seqretry(&base->lock, sequence);

	seq = read_seqbegin(&base->lock);

	p = lookup(daddr, base, seq, NULL, &gc_cnt, &parent, &pp);

	invalidated = read_seqretry(&base->lock, seq);

	rcu_read_unlock();



	if (p)
@@ -428,20 +198,13 @@ struct inet_peer *inet_getpeer(struct inet_peer_base *base, 
	/* retry an exact lookup, taking the lock before.

	 * At least, nodes should be hot in our cache.

	 */

	parent = NULL;

	write_seqlock_bh(&base->lock);

relookup:

	p = lookup(daddr, stack, base);

	if (p != peer_avl_empty) {

		refcount_inc(&p->refcnt);

		write_sequnlock_bh(&base->lock);

		return p;

	}

	if (!gccnt) {

		gccnt = inet_peer_gc(base, stack, stackptr);

		if (gccnt && create)

			goto relookup;

	}

	p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;



	gc_cnt = 0;

	p = lookup(daddr, base, seq, gc_stack, &gc_cnt, &parent, &pp);

	if (!p && create) {

		p = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);

		if (p) {

			p->daddr = *daddr;

			refcount_set(&p->refcnt, 2);
@@ -452,12 +215,14 @@ struct inet_peer *inet_getpeer(struct inet_peer_base *base, 
			 * calculation of tokens is at its maximum.

			 */

			p->rate_last = jiffies - 60*HZ;

		INIT_LIST_HEAD(&p->gc_list);



		/* Link the node. */

		link_to_pool(p, base);

			rb_link_node(&p->rb_node, parent, pp);

			rb_insert_color(&p->rb_node, &base->rb_root);

			base->total++;

		}

	}

	if (gc_cnt)

		inet_peer_gc(base, gc_stack, gc_cnt);

	write_sequnlock_bh(&base->lock);



	return p;
@@ -467,8 +232,9 @@ EXPORT_SYMBOL_GPL(inet_getpeer); 
void inet_putpeer(struct inet_peer *p)

{

	p->dtime = (__u32)jiffies;

	smp_mb__before_atomic();

	refcount_dec(&p->refcnt);



	if (refcount_dec_and_test(&p->refcnt))

		call_rcu(&p->rcu, inetpeer_free_rcu);

}

EXPORT_SYMBOL_GPL(inet_putpeer);
@@ -513,30 +279,16 @@ bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout) 
}

EXPORT_SYMBOL(inet_peer_xrlim_allow);



static void inetpeer_inval_rcu(struct rcu_head *head)

{

	struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu);



	spin_lock_bh(&gc_lock);

	list_add_tail(&p->gc_list, &gc_list);

	spin_unlock_bh(&gc_lock);



	schedule_delayed_work(&gc_work, gc_delay);

}



void inetpeer_invalidate_tree(struct inet_peer_base *base)

{

	struct inet_peer *root;



	write_seqlock_bh(&base->lock);

	struct inet_peer *p, *n;



	root = rcu_deref_locked(base->root, base);

	if (root != peer_avl_empty) {

		base->root = peer_avl_empty_rcu;

		base->total = 0;

		call_rcu(&root->gc_rcu, inetpeer_inval_rcu);

	rbtree_postorder_for_each_entry_safe(p, n, &base->rb_root, rb_node) {

		inet_putpeer(p);

		cond_resched();

	}



	write_sequnlock_bh(&base->lock);

	base->rb_root = RB_ROOT;

	base->total = 0;

}

EXPORT_SYMBOL(inetpeer_invalidate_tree);