bonding: delete migrated IP addresses from the rlb hash table

Bonding in balance-alb mode records information from ARP packets
passing through the bond in a hash table (rx_hashtbl).

At certain situations (e.g. link change of a slave),
rlb_update_rx_clients() will send out ARP packets to update ARP
caches of other hosts on the network to achieve RX load
balancing.

The problem is that once an IP address is recorded in the hash
table, it stays there indefinitely. If this IP address is
migrated to a different host in the network, bonding still sends
out ARP packets that poison other systems' ARP caches with
invalid information.

This patch solves this by looking at all incoming ARP packets,
and checking if the source IP address is one of the source
addresses stored in the rx_hashtbl. If it is, but the MAC
addresses differ, the corresponding hash table entries are
removed. Thus, when an IP address is migrated, the first ARP
broadcast by its new owner will purge the offending entries of
rx_hashtbl.

The hash table is hashed by ip_dst. To be able to do the above
check efficiently (not walking the whole hash table), we need a
reverse mapping (by ip_src).

I added three new members in struct rlb_client_info:
   rx_hashtbl[x].src_first will point to the start of a list of
      entries for which hash(ip_src) == x.
   The list is linked with src_next and src_prev.

When an incoming ARP packet arrives at rlb_arp_recv()
rlb_purge_src_ip() can quickly walk only the entries on the
corresponding lists, i.e. the entries that are likely to contain
the offending IP address.

To avoid confusion, I renamed these existing fields of struct
rlb_client_info:
	next -> used_next
	prev -> used_prev
	rx_hashtbl_head -> rx_hashtbl_used_head

(The current linked list is _not_ a list of hash table
entries with colliding ip_dst. It's a list of entries that are
being used; its purpose is to avoid walking the whole hash table
when looking for used entries.)
Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_alb.h

@@ -94,15 +94,35 @@ struct tlb_client_info {
 
 /* -------------------------------------------------------------------------
  * struct rlb_client_info contains all info related to a specific rx client
- * connection. This is the Clients Hash Table entry struct
+ * connection. This is the Clients Hash Table entry struct.
+ * Note that this is not a proper hash table; if a new client's IP address
+ * hash collides with an existing client entry, the old entry is replaced.
+ *
+ * There is a linked list (linked by the used_next and used_prev members)
+ * linking all the used entries of the hash table. This allows updating
+ * all the clients without walking over all the unused elements of the table.
+ *
+ * There are also linked lists of entries with identical hash(ip_src). These
+ * allow cleaning up the table from ip_src<->mac_src associations that have
+ * become outdated and would cause sending out invalid ARP updates to the
+ * network. These are linked by the (src_next and src_prev members).
  * -------------------------------------------------------------------------
  */
 struct rlb_client_info {
 	__be32 ip_src;		/* the server IP address */
 	__be32 ip_dst;		/* the client IP address */
+	u8  mac_src[ETH_ALEN];	/* the server MAC address */
 	u8  mac_dst[ETH_ALEN];	/* the client MAC address */
-	u32 next;		/* The next Hash table entry index */
-	u32 prev;		/* The previous Hash table entry index */
+
+	/* list of used hash table entries, starting at rx_hashtbl_used_head */
+	u32 used_next;
+	u32 used_prev;
+
+	/* ip_src based hashing */
+	u32 src_next;	/* next entry with same hash(ip_src) */
+	u32 src_prev;	/* prev entry with same hash(ip_src) */
+	u32 src_first;	/* first entry with hash(ip_src) == this entry's index */
+
 	u8  assigned;		/* checking whether this entry is assigned */
 	u8  ntt;		/* flag - need to transmit client info */
 	struct slave *slave;	/* the slave assigned to this client */
@@ -131,7 +151,7 @@ struct alb_bond_info {
 	int rlb_enabled;
 	struct rlb_client_info	*rx_hashtbl;	/* Receive hash table */
 	spinlock_t		rx_hashtbl_lock;
-	u32			rx_hashtbl_head;
+	u32			rx_hashtbl_used_head;
 	u8			rx_ntt;	/* flag - need to transmit
 					 * to all rx clients
 					 */

drivers/net/bonding/bond_debugfs.c

@@ -31,8 +31,9 @@ static int bond_debug_rlb_hash_show(struct seq_file *m, void *v)
 
 	spin_lock_bh(&(BOND_ALB_INFO(bond).rx_hashtbl_lock));
 
-	hash_index = bond_info->rx_hashtbl_head;
-	for (; hash_index != RLB_NULL_INDEX; hash_index = client_info->next) {
+	hash_index = bond_info->rx_hashtbl_used_head;
+	for (; hash_index != RLB_NULL_INDEX;
+	     hash_index = client_info->used_next) {
 		client_info = &(bond_info->rx_hashtbl[hash_index]);
 		seq_printf(m, "%-15pI4 %-15pI4 %-17pM %s\n",
 			&client_info->ip_src,