net: sched: flower: add reference counter to flower mask

Extend fl_flow_mask structure with reference counter to allow parallel
modification without relying on rtnl lock. Use rcu read lock to safely
lookup mask and increment reference counter in order to accommodate
concurrent deletes.
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_flower.c

@@ -76,6 +76,7 @@ struct fl_flow_mask {
 	struct list_head filters;
 	struct rcu_work rwork;
 	struct list_head list;
+	refcount_t refcnt;
 };
 
 struct fl_flow_tmplt {
@@ -320,6 +321,7 @@ static int fl_init(struct tcf_proto *tp)
 
 static void fl_mask_free(struct fl_flow_mask *mask)
 {
+	WARN_ON(!list_empty(&mask->filters));
 	rhashtable_destroy(&mask->ht);
 	kfree(mask);
 }
@@ -335,7 +337,7 @@ static void fl_mask_free_work(struct work_struct *work)
 static bool fl_mask_put(struct cls_fl_head *head, struct fl_flow_mask *mask,
 			bool async)
 {
-	if (!list_empty(&mask->filters))
+	if (!refcount_dec_and_test(&mask->refcnt))
 		return false;
 
 	rhashtable_remove_fast(&head->ht, &mask->ht_node, mask_ht_params);
@@ -1301,6 +1303,7 @@ static struct fl_flow_mask *fl_create_new_mask(struct cls_fl_head *head,
 
 	INIT_LIST_HEAD_RCU(&newmask->filters);
 
+	refcount_set(&newmask->refcnt, 1);
 	err = rhashtable_insert_fast(&head->ht, &newmask->ht_node,
 				     mask_ht_params);
 	if (err)
@@ -1324,9 +1327,13 @@ static int fl_check_assign_mask(struct cls_fl_head *head,
 				struct fl_flow_mask *mask)
 {
 	struct fl_flow_mask *newmask;
+	int ret = 0;
 
+	rcu_read_lock();
 	fnew->mask = rhashtable_lookup_fast(&head->ht, mask, mask_ht_params);
 	if (!fnew->mask) {
+		rcu_read_unlock();
+
 		if (fold)
 			return -EINVAL;
 
@@ -1335,11 +1342,15 @@ static int fl_check_assign_mask(struct cls_fl_head *head,
 			return PTR_ERR(newmask);
 
 		fnew->mask = newmask;
+		return 0;
 	} else if (fold && fold->mask != fnew->mask) {
-		return -EINVAL;
+		ret = -EINVAL;
+	} else if (!refcount_inc_not_zero(&fnew->mask->refcnt)) {
+		/* Mask was deleted concurrently, try again */
+		ret = -EAGAIN;
 	}
-
-	return 0;
+	rcu_read_unlock();
+	return ret;
 }
 
 static int fl_set_parms(struct net *net, struct tcf_proto *tp,
@@ -1476,6 +1487,7 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 		list_replace_rcu(&fold->list, &fnew->list);
 		fold->deleted = true;
 
+		fl_mask_put(head, fold->mask, true);
 		if (!tc_skip_hw(fold->flags))
 			fl_hw_destroy_filter(tp, fold, NULL);
 		tcf_unbind_filter(tp, &fold->res);
@@ -1525,7 +1537,7 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 	if (!tc_skip_hw(fnew->flags))
 		fl_hw_destroy_filter(tp, fnew, NULL);
 errout_mask:
-	fl_mask_put(head, fnew->mask, false);
+	fl_mask_put(head, fnew->mask, true);
 errout:
 	tcf_exts_destroy(&fnew->exts);
 	kfree(fnew);