mptcp: add userspace pm addr entry refcount

This patch adds the refcount of addree entry in userspace PM. Add a new
counter 'refcnt' in struct mptcp_pm_addr_entry, initiated to 1.

Increase this counter when an address is announced or a subflow is created
in mptcp_pm_nl_announce_doit() and mptcp_pm_nl_subflow_create_doit(). And
decrease it when an address is removed or a subflow is closed in
mptcp_pm_nl_remove_doit() and mptcp_userspace_pm_delete_local_addr(). If
the counter reaches to 1, free this entry.

Closes: multipath-tcp#403
Fixes: 24430f8 ("mptcp: add address into userspace pm list")
Signed-off-by: Geliang Tang <geliang.tang@linux.dev>

net/mptcp/pm_userspace.c

@@ -64,6 +64,7 @@ static int mptcp_userspace_pm_append_new_local_addr(struct mptcp_sock *msk,
 						1);
 	list_add_tail_rcu(&e->list, &msk->pm.userspace_pm_local_addr_list);
 	msk->pm.local_addr_used++;
+	refcount_set(&e->refcnt, 1);
 	ret = e->addr.id;
 
 append_err:
@@ -96,12 +97,11 @@ static int mptcp_userspace_pm_delete_local_addr(struct mptcp_sock *msk,
 
 	entry = mptcp_userspace_pm_get_entry(msk, &addr->addr);
 	if (entry) {
-		/* TODO: a refcount is needed because the entry can
-		 * be used multiple times (e.g. fullmesh mode).
-		 */
-		list_del_rcu(&entry->list);
-		kfree(entry);
-		msk->pm.local_addr_used--;
+		if (!refcount_dec_not_one(&entry->refcnt)) {
+			list_del_rcu(&entry->list);
+			kfree(entry);
+			msk->pm.local_addr_used--;
+		}
 		return 0;
 	}
 
@@ -213,6 +213,11 @@ int mptcp_pm_nl_announce_doit(struct sk_buff *skb, struct genl_info *info)
 	spin_lock_bh(&msk->pm.lock);
 
 	if (mptcp_pm_alloc_anno_list(msk, &addr_val.addr)) {
+		struct mptcp_pm_addr_entry *entry;
+
+		entry = mptcp_userspace_pm_get_entry(msk, &addr_val.addr);
+		if (entry && !refcount_inc_not_zero(&entry->refcnt))
+			pr_debug("userspace pm uninitialized entry");
 		msk->pm.add_addr_signaled++;
 		mptcp_pm_announce_addr(msk, &addr_val.addr, false);
 		mptcp_pm_nl_addr_send_ack(msk);
@@ -318,8 +323,10 @@ int mptcp_pm_nl_remove_doit(struct sk_buff *skb, struct genl_info *info)
 
 	mptcp_pm_remove_addrs(msk, &free_list);
 
-	list_del_rcu(&match->list);
-	kfree(match);
+	if (!refcount_dec_not_one(&match->refcnt)) {
+		list_del_rcu(&match->list);
+		kfree(match);
+	}
 
 	release_sock(sk);
 
@@ -403,10 +410,16 @@ int mptcp_pm_nl_subflow_create_doit(struct sk_buff *skb, struct genl_info *info)
 	release_sock(sk);
 
 	spin_lock_bh(&msk->pm.lock);
-	if (err)
+	if (err) {
 		mptcp_userspace_pm_delete_local_addr(msk, &local);
-	else
+	} else {
+		struct mptcp_pm_addr_entry *entry;
+
+		entry = mptcp_userspace_pm_get_entry(msk, &local.addr);
+		if (entry && !refcount_inc_not_zero(&entry->refcnt))
+			pr_debug("userspace pm uninitialized entry");
 		msk->pm.subflows++;
+	}
 	spin_unlock_bh(&msk->pm.lock);
 
  create_err:

net/mptcp/protocol.h

@@ -8,6 +8,7 @@
 #define __MPTCP_PROTOCOL_H
 
 #include <linux/random.h>
+#include <linux/refcount.h>
 #include <net/tcp.h>
 #include <net/inet_connection_sock.h>
 #include <uapi/linux/mptcp.h>
@@ -242,6 +243,7 @@ struct mptcp_pm_addr_entry {
 	u8			flags;
 	int			ifindex;
 	struct socket		*lsk;
+	refcount_t		refcnt;
 };
 
 struct mptcp_data_frag {