ipv6: Avoid redoing fib6_lookup() with reachable = 0 by saving fn

This patch save the fn before doing rt6_backtrack.
Hence, without redo-ing the fib6_lookup(), saved_fn can be used
to redo rt6_select() with RT6_LOOKUP_F_REACHABLE off.

Some minor changes I think make sense to review as a single patch:
* Remove the 'out:' goto label.
* Remove the 'reachable' variable. Only use the 'strict' variable instead.

After this patch, "failing ip6_ins_rt()" should be the only case that
requires a redo of fib6_lookup().

Cc: David Miller <davem@davemloft.net>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -917,31 +917,40 @@ static struct rt6_info *rt6_alloc_clone(struct rt6_info *ort,
 static struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table, int oif,
 				      struct flowi6 *fl6, int flags)
 {
-	struct fib6_node *fn;
+	struct fib6_node *fn, *saved_fn;
 	struct rt6_info *rt, *nrt;
 	int strict = 0;
 	int attempts = 3;
 	int err;
-	int reachable = net->ipv6.devconf_all->forwarding ? 0 : RT6_LOOKUP_F_REACHABLE;
 
 	strict |= flags & RT6_LOOKUP_F_IFACE;
+	if (net->ipv6.devconf_all->forwarding == 0)
+		strict |= RT6_LOOKUP_F_REACHABLE;
 
 redo_fib6_lookup_lock:
 	read_lock_bh(&table->tb6_lock);
 
-redo_fib6_lookup:
 	fn = fib6_lookup(&table->tb6_root, &fl6->daddr, &fl6->saddr);
+	saved_fn = fn;
 
 redo_rt6_select:
-	rt = rt6_select(fn, oif, strict | reachable);
+	rt = rt6_select(fn, oif, strict);
 	if (rt->rt6i_nsiblings)
-		rt = rt6_multipath_select(rt, fl6, oif, strict | reachable);
+		rt = rt6_multipath_select(rt, fl6, oif, strict);
 	if (rt == net->ipv6.ip6_null_entry) {
 		fn = fib6_backtrack(fn, &fl6->saddr);
 		if (fn)
 			goto redo_rt6_select;
-		else
-			goto out;
+		else if (strict & RT6_LOOKUP_F_REACHABLE) {
+			/* also consider unreachable route */
+			strict &= ~RT6_LOOKUP_F_REACHABLE;
+			fn = saved_fn;
+			goto redo_rt6_select;
+		} else {
+			dst_hold(&rt->dst);
+			read_unlock_bh(&table->tb6_lock);
+			goto out2;
+		}
 	}
 
 	dst_hold(&rt->dst);
@@ -977,13 +986,6 @@ static struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
 	ip6_rt_put(rt);
 	goto redo_fib6_lookup_lock;
 
-out:
-	if (reachable) {
-		reachable = 0;
-		goto redo_fib6_lookup;
-	}
-	dst_hold(&rt->dst);
-	read_unlock_bh(&table->tb6_lock);
 out2:
 	rt->dst.lastuse = jiffies;
 	rt->dst.__use++;