inet: Add family scope inetpeer flushes.

This implementation can deal with having many inetpeer roots, which is
a necessary prerequisite for per-FIB table rooted peer tables.

Each family (AF_INET, AF_INET6) has a sequence number which we bump
when we get a family invalidation request.

Each peer lookup cheaply checks whether the flush sequence of the
root we are using is out of date, and if so flushes it and updates
the sequence number.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/inetpeer.h

@@ -68,6 +68,7 @@ struct inet_peer {
 struct inet_peer_base {
 	struct inet_peer __rcu	*root;
 	seqlock_t		lock;
+	u32			flush_seq;
 	int			total;
 };
 
@@ -168,6 +169,7 @@ extern void inet_putpeer(struct inet_peer *p);
 extern bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout);
 
 extern void inetpeer_invalidate_tree(struct inet_peer_base *);
+extern void inetpeer_invalidate_family(int family);
 
 /*
  * temporary check to make sure we dont access rid, ip_id_count, tcp_ts,

net/ipv4/inetpeer.c

@@ -86,10 +86,36 @@ void inet_peer_base_init(struct inet_peer_base *bp)
 {
 	bp->root = peer_avl_empty_rcu;
 	seqlock_init(&bp->lock);
+	bp->flush_seq = ~0U;
 	bp->total = 0;
 }
 EXPORT_SYMBOL_GPL(inet_peer_base_init);
 
+static atomic_t v4_seq = ATOMIC_INIT(0);
+static atomic_t v6_seq = ATOMIC_INIT(0);
+
+static atomic_t *inetpeer_seq_ptr(int family)
+{
+	return (family == AF_INET ? &v4_seq : &v6_seq);
+}
+
+static inline void flush_check(struct inet_peer_base *base, int family)
+{
+	atomic_t *fp = inetpeer_seq_ptr(family);
+
+	if (unlikely(base->flush_seq != atomic_read(fp))) {
+		inetpeer_invalidate_tree(base);
+		base->flush_seq = atomic_read(fp);
+	}
+}
+
+void inetpeer_invalidate_family(int family)
+{
+	atomic_t *fp = inetpeer_seq_ptr(family);
+
+	atomic_inc(fp);
+}
+
 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
 
 /* Exported for sysctl_net_ipv4.  */
@@ -437,6 +463,8 @@ struct inet_peer *inet_getpeer(struct inet_peer_base *base,
 	unsigned int sequence;
 	int invalidated, gccnt = 0;
 
+	flush_check(base, daddr->family);
+
 	/* Attempt a lockless lookup first.
 	 * Because of a concurrent writer, we might not find an existing entry.
 	 */

net/ipv4/route.c

@@ -935,7 +935,7 @@ static void rt_cache_invalidate(struct net *net)
 
 	get_random_bytes(&shuffle, sizeof(shuffle));
 	atomic_add(shuffle + 1U, &net->ipv4.rt_genid);
-	inetpeer_invalidate_tree(net->ipv4.peers);
+	inetpeer_invalidate_family(AF_INET);
 }
 
 /*