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

[Eric Dumazet <eric.dumazet@gmail.com>]

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);
}