Re: [PATCH 09/15] ipv4: Cache output routes in fib_info nexthops.

On Wed, 2012-07-18 at 11:24 -0700, David Miller wrote:

If we have an output route that lacks nexthop exceptions, we can cache
it in the FIB info nexthop.

Such routes will have DST_HOST cleared because such routes refer to a
family of destinations, rather than just one.

-			   const struct fib_result *res,
+static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
+{
+	static DEFINE_SPINLOCK(fib_cache_lock);
+	struct rtable **p = &nh->nh_rth_output;
+
+	if (*p)
+		return;
+
+	spin_lock_bh(&fib_cache_lock);
+	if (!*p) {
+		*p = rt;
+		dst_clone(&rt->dst);
+	}
+	spin_unlock_bh(&fib_cache_lock);
+}
+

This probably should use cmpxchg()

static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
{
	struct rtable **p = &nh->nh_rth_output;

	if (*p)
               return;

	if (cmpxchg(p, NULL, rt) == NULL)
		dst_clone(&rt->dst);
}