This patch adds userspace PM address entry refcont. Add a new refcont
filed in struct mptcp_pm_addr_entry, inited to 1, and another filed
subflows, inited to 0, to store how many subflows have been established
on this address entry.

Increase both values in mptcp_nl_cmd_sf_create(), and decrease refcont
in mptcp_userspace_pm_delete_local_addr() according the subflows value.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/pm_userspace.c | 27 +++++++++++++++++++++------
 net/mptcp/protocol.h     |  3 +++
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index 359ecc65fc73..091f299db010 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -70,6 +70,8 @@ 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++;
+		e->subflows = 0;
+		refcount_set(&e->refcnt, 1);
 		ret = e->addr.id;
 	} else if (match) {
 		ret = entry->addr.id;
@@ -102,14 +104,20 @@ static int mptcp_userspace_pm_delete_local_addr(struct mptcp_sock *msk,
 						struct mptcp_pm_addr_entry *addr)
 {
 	struct mptcp_pm_addr_entry *entry;
+	int i;
 
 	entry = mptcp_userspace_pm_get_entry(msk, &addr->addr);
 	if (!entry)
 		return -EINVAL;
 
-	/* TODO: a refcount is needed because the entry can
-	 * be used multiple times (e.g. fullmesh mode).
-	 */
+	for (i = 0; i < entry->subflows; i++) {
+		if (!refcount_dec_not_one(&entry->refcnt)) {
+			pr_debug("userspace refcount error: refcnt=%d, subflows=%d",
+				 refcount_read(&entry->refcnt), entry->subflows);
+			return -EINVAL;
+		}
+	}
+
 	list_del_rcu(&entry->list);
 	kfree(entry);
 	msk->pm.local_addr_used--;
@@ -380,10 +388,17 @@ int mptcp_nl_cmd_sf_create(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
-		msk->pm.subflows++;
+	} else {
+		struct mptcp_pm_addr_entry *entry;
+
+		entry = mptcp_userspace_pm_get_entry(msk, &addr_l);
+		if (entry && refcount_inc_not_zero(&entry->refcnt)) {
+			msk->pm.subflows++;
+			entry->subflows++;
+		}
+	}
 	spin_unlock_bh(&msk->pm.lock);
 
  create_err:
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 15c85be21fd9..06465c8c21e4 100644
--- a/net/mptcp/protocol.h
+++ b/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>
@@ -241,6 +242,8 @@ struct mptcp_pm_addr_entry {
 	u8			flags;
 	int			ifindex;
 	struct socket		*lsk;
+	u8			subflows;
+	refcount_t		refcnt;
 };
 
 struct mptcp_data_frag {
-- 
2.35.3