net: sched: cls_matchall: allow to delete filter

Currently user is unable to delete the filter. See following example:
$ tc filter add dev ens16np1 ingress pref 1 handle 1 matchall action drop
$ tc filter show dev ens16np1 ingress
filter protocol all pref 1 matchall chain 0
filter protocol all pref 1 matchall chain 0 handle 0x1
  in_hw
        action order 1: gact action drop
         random type none pass val 0
         index 1 ref 1 bind 1

$ tc filter del dev ens16np1 ingress pref 1 handle 1 matchall action drop
RTNETLINK answers: Operation not supported

Implement tcf_proto_ops->delete() op and allow user to delete the filter.
Reported-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_matchall.c

@@ -21,6 +21,7 @@ struct cls_mall_head {
 	unsigned int in_hw_count;
 	struct tc_matchall_pcnt __percpu *pf;
 	struct rcu_work rwork;
+	bool deleting;
 };
 
 static int mall_classify(struct sk_buff *skb, const struct tcf_proto *tp,
@@ -258,7 +259,11 @@ static int mall_change(struct net *net, struct sk_buff *in_skb,
 static int mall_delete(struct tcf_proto *tp, void *arg, bool *last,
 		       bool rtnl_held, struct netlink_ext_ack *extack)
 {
-	return -EOPNOTSUPP;
+	struct cls_mall_head *head = rtnl_dereference(tp->root);
+
+	head->deleting = true;
+	*last = true;
+	return 0;
 }
 
 static void mall_walk(struct tcf_proto *tp, struct tcf_walker *arg,
@@ -269,7 +274,7 @@ static void mall_walk(struct tcf_proto *tp, struct tcf_walker *arg,
 	if (arg->count < arg->skip)
 		goto skip;
 
-	if (!head)
+	if (!head || head->deleting)
 		return;
 	if (arg->fn(tp, head, arg) < 0)
 		arg->stop = 1;