NFS: Lockless DNS lookups

Enable RCU protected lookup in the legacy DNS resolver.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfs/dns_resolve.c

@@ -65,6 +65,7 @@ struct nfs_dns_ent {
 
 	struct sockaddr_storage addr;
 	size_t addrlen;
+	struct rcu_head rcu_head;
 };
 
 
@@ -101,15 +102,23 @@ static void nfs_dns_ent_init(struct cache_head *cnew,
 	}
 }
 
-static void nfs_dns_ent_put(struct kref *ref)
+static void nfs_dns_ent_free_rcu(struct rcu_head *head)
 {
 	struct nfs_dns_ent *item;
 
-	item = container_of(ref, struct nfs_dns_ent, h.ref);
+	item = container_of(head, struct nfs_dns_ent, rcu_head);
 	kfree(item->hostname);
 	kfree(item);
 }
 
+static void nfs_dns_ent_put(struct kref *ref)
+{
+	struct nfs_dns_ent *item;
+
+	item = container_of(ref, struct nfs_dns_ent, h.ref);
+	call_rcu(item, nfs_dns_ent_free_rcu);
+}
+
 static struct cache_head *nfs_dns_ent_alloc(void)
 {
 	struct nfs_dns_ent *item = kmalloc(sizeof(*item), GFP_KERNEL);
@@ -195,7 +204,7 @@ static struct nfs_dns_ent *nfs_dns_lookup(struct cache_detail *cd,
 {
 	struct cache_head *ch;
 
-	ch = sunrpc_cache_lookup(cd,
+	ch = sunrpc_cache_lookup_rcu(cd,
 			&key->h,
 			nfs_dns_hash(key));
 	if (!ch)