instance_create(u_int16_t group_num, int pid)
 {
        struct nfulnl_instance *inst;
+       int err;
 
        write_lock_bh(&instances_lock);
        if (__instance_lookup(group_num)) {
-               inst = NULL;
+               err = -EEXIST;
                goto out_unlock;
        }
 
        inst = kzalloc(sizeof(*inst), GFP_ATOMIC);
-       if (!inst)
+       if (!inst) {
+               err = -ENOMEM;
                goto out_unlock;
+       }
 
        if (!try_module_get(THIS_MODULE)) {
                kfree(inst);
+               err = -EAGAIN;
                goto out_unlock;
        }
 
 
 out_unlock:
        write_unlock_bh(&instances_lock);
-       return NULL;
+       return ERR_PTR(err);
 }
 
 static void __nfulnl_flush(struct nfulnl_instance *inst);
 
                        inst = instance_create(group_num,
                                               NETLINK_CB(skb).pid);
-                       if (!inst) {
-                               ret = -EINVAL;
+                       if (IS_ERR(inst)) {
+                               ret = PTR_ERR(inst);
                                goto out;
                        }
                        break;
 
 static struct nfqnl_instance *
 instance_create(u_int16_t queue_num, int pid)
 {
-       struct nfqnl_instance *inst = NULL;
+       struct nfqnl_instance *inst;
        unsigned int h;
+       int err;
 
        spin_lock(&instances_lock);
-       if (instance_lookup(queue_num))
+       if (instance_lookup(queue_num)) {
+               err = -EEXIST;
                goto out_unlock;
+       }
 
        inst = kzalloc(sizeof(*inst), GFP_ATOMIC);
-       if (!inst)
+       if (!inst) {
+               err = -ENOMEM;
                goto out_unlock;
+       }
 
        inst->queue_num = queue_num;
        inst->peer_pid = pid;
        INIT_LIST_HEAD(&inst->queue_list);
        INIT_RCU_HEAD(&inst->rcu);
 
-       if (!try_module_get(THIS_MODULE))
+       if (!try_module_get(THIS_MODULE)) {
+               err = -EAGAIN;
                goto out_free;
+       }
 
        h = instance_hashfn(queue_num);
        hlist_add_head_rcu(&inst->hlist, &instance_table[h]);
        kfree(inst);
 out_unlock:
        spin_unlock(&instances_lock);
-       return NULL;
+       return ERR_PTR(err);
 }
 
 static void nfqnl_flush(struct nfqnl_instance *queue, nfqnl_cmpfn cmpfn,
                                goto err_out_unlock;
                        }
                        queue = instance_create(queue_num, NETLINK_CB(skb).pid);
-                       if (!queue) {
-                               ret = -EINVAL;
+                       if (IS_ERR(queue)) {
+                               ret = PTR_ERR(queue);
                                goto err_out_unlock;
                        }
                        break;