net_sched: destroy proto tp when all filters are gone

Kernel automatically creates a tp for each
(kind, protocol, priority) tuple, which has handle 0,
when we add a new filter, but it still is left there
after we remove our own, unless we don't specify the
handle (literally means all the filters under
the tuple). For example this one is left:

# tc filter show dev eth0
filter parent 8001: protocol arp pref 49152 basic

The user-space is hard to clean up these for kernel
because filters like u32 are organized in a complex way.
So kernel is responsible to remove it after all filters
are gone. Each type of filter has its own way to
store the filters, so each type has to provide its
way to check if all filters are gone.

Cc: Jamal Hadi Salim <[e-mail]>
Signed-off-by: Cong Wang <[e-mail]>
Signed-off-by: Cong Wang <[e-mail]>
Acked-by: Jamal Hadi Salim<[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/sch_generic.h

···
 					    const struct tcf_proto *,
 					    struct tcf_result *);
 	int			(*init)(struct tcf_proto*);
-	void			(*destroy)(struct tcf_proto*);
+	bool			(*destroy)(struct tcf_proto*, bool);
 
 	unsigned long		(*get)(struct tcf_proto*, u32 handle);
 	int			(*change)(struct net *net, struct sk_buff *,
···
 				const struct Qdisc_ops *ops, u32 parentid);
 void __qdisc_calculate_pkt_len(struct sk_buff *skb,
 			       const struct qdisc_size_table *stab);
-void tcf_destroy(struct tcf_proto *tp);
+bool tcf_destroy(struct tcf_proto *tp, bool force);
 void tcf_destroy_chain(struct tcf_proto __rcu **fl);
 
 /* Reset all TX qdiscs greater then index of a device.  */

net/sched/cls_api.c

···
 			RCU_INIT_POINTER(*back, next);
 
 			tfilter_notify(net, skb, n, tp, fh, RTM_DELTFILTER);
-			tcf_destroy(tp);
+			tcf_destroy(tp, true);
 			err = 0;
 			goto errout;
 		}
···
 			err = -EEXIST;
 			if (n->nlmsg_flags & NLM_F_EXCL) {
 				if (tp_created)
-					tcf_destroy(tp);
+					tcf_destroy(tp, true);
 				goto errout;
 			}
 			break;
 		case RTM_DELTFILTER:
 			err = tp->ops->delete(tp, fh);
-			if (err == 0)
+			if (err == 0) {
 				tfilter_notify(net, skb, n, tp, fh, RTM_DELTFILTER);
+				if (tcf_destroy(tp, false)) {
+					struct tcf_proto *next = rtnl_dereference(tp->next);
+
+					RCU_INIT_POINTER(*back, next);
+				}
+			}
 			goto errout;
 		case RTM_GETTFILTER:
 			err = tfilter_notify(net, skb, n, tp, fh, RTM_NEWTFILTER);
···
 		tfilter_notify(net, skb, n, tp, fh, RTM_NEWTFILTER);
 	} else {
 		if (tp_created)
-			tcf_destroy(tp);
+			tcf_destroy(tp, true);
 	}
 
 errout:

net/sched/cls_basic.c

···
 	kfree(f);
 }
 
-static void basic_destroy(struct tcf_proto *tp)
+static bool basic_destroy(struct tcf_proto *tp, bool force)
 {
 	struct basic_head *head = rtnl_dereference(tp->root);
 	struct basic_filter *f, *n;
+
+	if (!force && !list_empty(&head->flist))
+		return false;
 
 	list_for_each_entry_safe(f, n, &head->flist, link) {
 		list_del_rcu(&f->link);
···
 	}
 	RCU_INIT_POINTER(tp->root, NULL);
 	kfree_rcu(head, rcu);
+	return true;
 }
 
 static int basic_delete(struct tcf_proto *tp, unsigned long arg)

net/sched/cls_bpf.c

···
 	return 0;
 }
 
-static void cls_bpf_destroy(struct tcf_proto *tp)
+static bool cls_bpf_destroy(struct tcf_proto *tp, bool force)
 {
 	struct cls_bpf_head *head = rtnl_dereference(tp->root);
 	struct cls_bpf_prog *prog, *tmp;
+
+	if (!force && !list_empty(&head->plist))
+		return false;
 
 	list_for_each_entry_safe(prog, tmp, &head->plist, link) {
 		list_del_rcu(&prog->link);
···
 
 	RCU_INIT_POINTER(tp->root, NULL);
 	kfree_rcu(head, rcu);
+	return true;
 }
 
 static unsigned long cls_bpf_get(struct tcf_proto *tp, u32 handle)

net/sched/cls_cgroup.c

···
 	return err;
 }
 
-static void cls_cgroup_destroy(struct tcf_proto *tp)
+static bool cls_cgroup_destroy(struct tcf_proto *tp, bool force)
 {
 	struct cls_cgroup_head *head = rtnl_dereference(tp->root);
+
+	if (!force)
+		return false;
 
 	if (head) {
 		RCU_INIT_POINTER(tp->root, NULL);
 		call_rcu(&head->rcu, cls_cgroup_destroy_rcu);
 	}
+	return true;
 }
 
 static int cls_cgroup_delete(struct tcf_proto *tp, unsigned long arg)

net/sched/cls_flow.c

···
 	return 0;
 }
 
-static void flow_destroy(struct tcf_proto *tp)
+static bool flow_destroy(struct tcf_proto *tp, bool force)
 {
 	struct flow_head *head = rtnl_dereference(tp->root);
 	struct flow_filter *f, *next;
+
+	if (!force && !list_empty(&head->filters))
+		return false;
 
 	list_for_each_entry_safe(f, next, &head->filters, list) {
 		list_del_rcu(&f->list);
···
 	}
 	RCU_INIT_POINTER(tp->root, NULL);
 	kfree_rcu(head, rcu);
+	return true;
 }
 
 static unsigned long flow_get(struct tcf_proto *tp, u32 handle)

net/sched/cls_fw.c

···
 	kfree(f);
 }
 
-static void fw_destroy(struct tcf_proto *tp)
+static bool fw_destroy(struct tcf_proto *tp, bool force)
 {
 	struct fw_head *head = rtnl_dereference(tp->root);
 	struct fw_filter *f;
 	int h;
 
 	if (head == NULL)
-		return;
+		return true;
+
+	if (!force) {
+		for (h = 0; h < HTSIZE; h++)
+			if (rcu_access_pointer(head->ht[h]))
+				return false;
+	}
 
 	for (h = 0; h < HTSIZE; h++) {
 		while ((f = rtnl_dereference(head->ht[h])) != NULL) {
···
 	}
 	RCU_INIT_POINTER(tp->root, NULL);
 	kfree_rcu(head, rcu);
+	return true;
 }
 
 static int fw_delete(struct tcf_proto *tp, unsigned long arg)

net/sched/cls_route.c

···
 	kfree(f);
 }
 
-static void route4_destroy(struct tcf_proto *tp)
+static bool route4_destroy(struct tcf_proto *tp, bool force)
 {
 	struct route4_head *head = rtnl_dereference(tp->root);
 	int h1, h2;
 
 	if (head == NULL)
-		return;
+		return true;
+
+	if (!force) {
+		for (h1 = 0; h1 <= 256; h1++) {
+			if (rcu_access_pointer(head->table[h1]))
+				return false;
+		}
+	}
 
 	for (h1 = 0; h1 <= 256; h1++) {
 		struct route4_bucket *b;
···
 	}
 	RCU_INIT_POINTER(tp->root, NULL);
 	kfree_rcu(head, rcu);
+	return true;
 }
 
 static int route4_delete(struct tcf_proto *tp, unsigned long arg)

net/sched/cls_rsvp.h

···
 	kfree_rcu(f, rcu);
 }
 
-static void rsvp_destroy(struct tcf_proto *tp)
+static bool rsvp_destroy(struct tcf_proto *tp, bool force)
 {
 	struct rsvp_head *data = rtnl_dereference(tp->root);
 	int h1, h2;
 
 	if (data == NULL)
-		return;
+		return true;
+
+	if (!force) {
+		for (h1 = 0; h1 < 256; h1++) {
+			if (rcu_access_pointer(data->ht[h1]))
+				return false;
+		}
+	}
 
 	RCU_INIT_POINTER(tp->root, NULL);
 
···
 		}
 	}
 	kfree_rcu(data, rcu);
+	return true;
 }
 
 static int rsvp_delete(struct tcf_proto *tp, unsigned long arg)

net/sched/cls_tcindex.c

···
 	}
 }
 
-static void tcindex_destroy(struct tcf_proto *tp)
+static bool tcindex_destroy(struct tcf_proto *tp, bool force)
 {
 	struct tcindex_data *p = rtnl_dereference(tp->root);
 	struct tcf_walker walker;
+
+	if (!force)
+		return false;
 
 	pr_debug("tcindex_destroy(tp %p),p %p\n", tp, p);
 	walker.count = 0;
···
 
 	RCU_INIT_POINTER(tp->root, NULL);
 	call_rcu(&p->rcu, __tcindex_destroy);
+	return true;
 }
 
 

net/sched/cls_u32.c

···
 	return -ENOENT;
 }
 
-static void u32_destroy(struct tcf_proto *tp)
+static bool ht_empty(struct tc_u_hnode *ht)
+{
+	unsigned int h;
+
+	for (h = 0; h <= ht->divisor; h++)
+		if (rcu_access_pointer(ht->ht[h]))
+			return false;
+
+	return true;
+}
+
+static bool u32_destroy(struct tcf_proto *tp, bool force)
 {
 	struct tc_u_common *tp_c = tp->data;
 	struct tc_u_hnode *root_ht = rtnl_dereference(tp->root);
 
 	WARN_ON(root_ht == NULL);
+
+	if (!force) {
+		if (root_ht) {
+			if (root_ht->refcnt > 1)
+				return false;
+			if (root_ht->refcnt == 1) {
+				if (!ht_empty(root_ht))
+					return false;
+			}
+		}
+	}
 
 	if (root_ht && --root_ht->refcnt == 0)
 		u32_destroy_hnode(tp, root_ht);
···
 	}
 
 	tp->data = NULL;
+	return true;
 }
 
 static int u32_delete(struct tcf_proto *tp, unsigned long arg)

net/sched/sch_api.c

···
 }
 EXPORT_SYMBOL(tc_classify);
 
-void tcf_destroy(struct tcf_proto *tp)
+bool tcf_destroy(struct tcf_proto *tp, bool force)
 {
-	tp->ops->destroy(tp);
-	module_put(tp->ops->owner);
-	kfree_rcu(tp, rcu);
+	if (tp->ops->destroy(tp, force)) {
+		module_put(tp->ops->owner);
+		kfree_rcu(tp, rcu);
+		return true;
+	}
+
+	return false;
 }
 
 void tcf_destroy_chain(struct tcf_proto __rcu **fl)
···
 
 	while ((tp = rtnl_dereference(*fl)) != NULL) {
 		RCU_INIT_POINTER(*fl, tp->next);
-		tcf_destroy(tp);
+		tcf_destroy(tp, true);
 	}
 }
 EXPORT_SYMBOL(tcf_destroy_chain);