neighbour: Create netdev->neighbour association

Create a mapping between a netdev and its neighoburs,
allowing for much cheaper flushes.

Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20241107160444.2913124-7-gnaaman@drivenets.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/net_cachelines/net_device.rst

@@ -188,4 +188,5 @@ u64                                 max_pacing_offload_horizon
 struct_napi_config*                 napi_config
 unsigned_long                       gro_flush_timeout
 u32                                 napi_defer_hard_irqs
+struct hlist_head                   neighbours[2]
 =================================== =========================== =================== =================== ===================================================================================

include/linux/netdevice.h

@@ -52,6 +52,7 @@
 #include <net/net_trackers.h>
 #include <net/net_debug.h>
 #include <net/dropreason-core.h>
+#include <net/neighbour_tables.h>
 
 struct netpoll_info;
 struct device;
@@ -2032,6 +2033,9 @@ enum netdev_reg_state {
  *	@napi_defer_hard_irqs:	If not zero, provides a counter that would
  *				allow to avoid NIC hard IRQ, on busy queues.
  *
+ *	@neighbours:	List heads pointing to this device's neighbours'
+ *			dev_list, one per address-family.
+ *
  *	FIXME: cleanup struct net_device such that network protocol info
  *	moves out.
  */
@@ -2440,6 +2444,9 @@ struct net_device {
 	 */
 	struct net_shaper_hierarchy *net_shaper_hierarchy;
 #endif
+
+	struct hlist_head neighbours[NEIGH_NR_TABLES];
+
 	u8			priv[] ____cacheline_aligned
 				       __counted_by(priv_len);
 } ____cacheline_aligned;

include/net/neighbour.h

@@ -29,6 +29,7 @@
 #include <linux/sysctl.h>
 #include <linux/workqueue.h>
 #include <net/rtnetlink.h>
+#include <net/neighbour_tables.h>
 
 /*
  * NUD stands for "neighbor unreachability detection"
@@ -136,6 +137,7 @@ struct neigh_statistics {
 
 struct neighbour {
 	struct hlist_node	hash;
+	struct hlist_node	dev_list;
 	struct neigh_table	*tbl;
 	struct neigh_parms	*parms;
 	unsigned long		confirmed;
@@ -236,13 +238,6 @@ struct neigh_table {
 	struct pneigh_entry	**phash_buckets;
 };
 
-enum {
-	NEIGH_ARP_TABLE = 0,
-	NEIGH_ND_TABLE = 1,
-	NEIGH_NR_TABLES,
-	NEIGH_LINK_TABLE = NEIGH_NR_TABLES /* Pseudo table for neigh_xmit */
-};
-
 static inline int neigh_parms_family(struct neigh_parms *p)
 {
 	return p->tbl->family;

include/net/neighbour_tables.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NET_NEIGHBOUR_TABLES_H
+#define _NET_NEIGHBOUR_TABLES_H
+
+enum {
+	NEIGH_ARP_TABLE = 0,
+	NEIGH_ND_TABLE = 1,
+	NEIGH_NR_TABLES,
+	NEIGH_LINK_TABLE = NEIGH_NR_TABLES /* Pseudo table for neigh_xmit */
+};
+
+#endif

net/core/neighbour.c

@@ -60,6 +60,25 @@ static int pneigh_ifdown_and_unlock(struct neigh_table *tbl,
 static const struct seq_operations neigh_stat_seq_ops;
 #endif
 
+static struct hlist_head *neigh_get_dev_table(struct net_device *dev, int family)
+{
+	int i;
+
+	switch (family) {
+	default:
+		DEBUG_NET_WARN_ON_ONCE(1);
+		fallthrough; /* to avoid panic by null-ptr-deref */
+	case AF_INET:
+		i = NEIGH_ARP_TABLE;
+		break;
+	case AF_INET6:
+		i = NEIGH_ND_TABLE;
+		break;
+	}
+
+	return &dev->neighbours[i];
+}
+
 /*
    Neighbour hash table buckets are protected with rwlock tbl->lock.
 
@@ -211,6 +230,7 @@ bool neigh_remove_one(struct neighbour *n)
 	write_lock(&n->lock);
 	if (refcount_read(&n->refcnt) == 1) {
 		hlist_del_rcu(&n->hash);
+		hlist_del_rcu(&n->dev_list);
 		neigh_mark_dead(n);
 		retval = true;
 	}
@@ -351,48 +371,42 @@ static void pneigh_queue_purge(struct sk_buff_head *list, struct net *net,
 static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
 			    bool skip_perm)
 {
-	int i;
-	struct neigh_hash_table *nht;
+	struct hlist_head *dev_head;
+	struct hlist_node *tmp;
+	struct neighbour *n;
 
-	nht = rcu_dereference_protected(tbl->nht,
-					lockdep_is_held(&tbl->lock));
+	dev_head = neigh_get_dev_table(dev, tbl->family);
 
-	for (i = 0; i < (1 << nht->hash_shift); i++) {
-		struct hlist_node *tmp;
-		struct neighbour *n;
+	hlist_for_each_entry_safe(n, tmp, dev_head, dev_list) {
+		if (skip_perm && n->nud_state & NUD_PERMANENT)
+			continue;
 
-		neigh_for_each_in_bucket_safe(n, tmp, &nht->hash_heads[i]) {
-			if (dev && n->dev != dev)
-				continue;
-			if (skip_perm && n->nud_state & NUD_PERMANENT)
-				continue;
-
-			hlist_del_rcu(&n->hash);
-			write_lock(&n->lock);
-			neigh_del_timer(n);
-			neigh_mark_dead(n);
-			if (refcount_read(&n->refcnt) != 1) {
-				/* The most unpleasant situation.
-				   We must destroy neighbour entry,
-				   but someone still uses it.
-
-				   The destroy will be delayed until
-				   the last user releases us, but
-				   we must kill timers etc. and move
-				   it to safe state.
-				 */
-				__skb_queue_purge(&n->arp_queue);
-				n->arp_queue_len_bytes = 0;
-				WRITE_ONCE(n->output, neigh_blackhole);
-				if (n->nud_state & NUD_VALID)
-					n->nud_state = NUD_NOARP;
-				else
-					n->nud_state = NUD_NONE;
-				neigh_dbg(2, "neigh %p is stray\n", n);
-			}
-			write_unlock(&n->lock);
-			neigh_cleanup_and_release(n);
+		hlist_del_rcu(&n->hash);
+		hlist_del_rcu(&n->dev_list);
+		write_lock(&n->lock);
+		neigh_del_timer(n);
+		neigh_mark_dead(n);
+		if (refcount_read(&n->refcnt) != 1) {
+			/* The most unpleasant situation.
+			 * We must destroy neighbour entry,
+			 * but someone still uses it.
+			 *
+			 * The destroy will be delayed until
+			 * the last user releases us, but
+			 * we must kill timers etc. and move
+			 * it to safe state.
+			 */
+			__skb_queue_purge(&n->arp_queue);
+			n->arp_queue_len_bytes = 0;
+			WRITE_ONCE(n->output, neigh_blackhole);
+			if (n->nud_state & NUD_VALID)
+				n->nud_state = NUD_NOARP;
+			else
+				n->nud_state = NUD_NONE;
+			neigh_dbg(2, "neigh %p is stray\n", n);
 		}
+		write_unlock(&n->lock);
+		neigh_cleanup_and_release(n);
 	}
 }
 
@@ -655,6 +669,10 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 	if (want_ref)
 		neigh_hold(n);
 	hlist_add_head_rcu(&n->hash, &nht->hash_heads[hash_val]);
+
+	hlist_add_head_rcu(&n->dev_list,
+			   neigh_get_dev_table(dev, tbl->family));
+
 	write_unlock_bh(&tbl->lock);
 	neigh_dbg(2, "neigh %p is created\n", n);
 	rc = n;
@@ -935,6 +953,7 @@ static void neigh_periodic_work(struct work_struct *work)
 			     !time_in_range_open(jiffies, n->used,
 						 n->used + NEIGH_VAR(n->parms, GC_STALETIME)))) {
 				hlist_del_rcu(&n->hash);
+				hlist_del_rcu(&n->dev_list);
 				neigh_mark_dead(n);
 				write_unlock(&n->lock);
 				neigh_cleanup_and_release(n);
@@ -3054,6 +3073,7 @@ void __neigh_for_each_release(struct neigh_table *tbl,
 			release = cb(n);
 			if (release) {
 				hlist_del_rcu(&n->hash);
+				hlist_del_rcu(&n->dev_list);
 				neigh_mark_dead(n);
 			}
 			write_unlock(&n->lock);