mptcp: use WRITE_ONCE for the pernet *_max

This patch uses WRITE_ONCE() for all the pernet add_addr_signal_max,
add_addr_accept_max, local_addr_max and subflows_max fields in struct
pm_nl_pernet to avoid concurrency issues.
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/pm_netlink.c

@@ -572,6 +572,7 @@ static int mptcp_pm_nl_append_new_local_addr(struct pm_nl_pernet *pernet,
 					     struct mptcp_pm_addr_entry *entry)
 {
 	struct mptcp_pm_addr_entry *cur;
+	unsigned int addr_max;
 	int ret = -EINVAL;
 
 	spin_lock_bh(&pernet->lock);
@@ -614,10 +615,14 @@ static int mptcp_pm_nl_append_new_local_addr(struct pm_nl_pernet *pernet,
 	if (entry->addr.id > pernet->next_id)
 		pernet->next_id = entry->addr.id;
 
-	if (entry->addr.flags & MPTCP_PM_ADDR_FLAG_SIGNAL)
-		pernet->add_addr_signal_max++;
-	if (entry->addr.flags & MPTCP_PM_ADDR_FLAG_SUBFLOW)
-		pernet->local_addr_max++;
+	if (entry->addr.flags & MPTCP_PM_ADDR_FLAG_SIGNAL) {
+		addr_max = pernet->add_addr_signal_max;
+		WRITE_ONCE(pernet->add_addr_signal_max, addr_max + 1);
+	}
+	if (entry->addr.flags & MPTCP_PM_ADDR_FLAG_SUBFLOW) {
+		addr_max = pernet->local_addr_max;
+		WRITE_ONCE(pernet->local_addr_max, addr_max + 1);
+	}
 
 	pernet->addrs++;
 	list_add_tail_rcu(&entry->list, &pernet->local_addr_list);
@@ -912,6 +917,7 @@ static int mptcp_nl_cmd_del_addr(struct sk_buff *skb, struct genl_info *info)
 	struct nlattr *attr = info->attrs[MPTCP_PM_ATTR_ADDR];
 	struct pm_nl_pernet *pernet = genl_info_pm_nl(info);
 	struct mptcp_pm_addr_entry addr, *entry;
+	unsigned int addr_max;
 	int ret;
 
 	ret = mptcp_pm_parse_addr(attr, info, false, &addr);
@@ -925,10 +931,14 @@ static int mptcp_nl_cmd_del_addr(struct sk_buff *skb, struct genl_info *info)
 		spin_unlock_bh(&pernet->lock);
 		return -EINVAL;
 	}
-	if (entry->addr.flags & MPTCP_PM_ADDR_FLAG_SIGNAL)
-		pernet->add_addr_signal_max--;
-	if (entry->addr.flags & MPTCP_PM_ADDR_FLAG_SUBFLOW)
-		pernet->local_addr_max--;
+	if (entry->addr.flags & MPTCP_PM_ADDR_FLAG_SIGNAL) {
+		addr_max = pernet->add_addr_signal_max;
+		WRITE_ONCE(pernet->add_addr_signal_max, addr_max - 1);
+	}
+	if (entry->addr.flags & MPTCP_PM_ADDR_FLAG_SUBFLOW) {
+		addr_max = pernet->local_addr_max;
+		WRITE_ONCE(pernet->local_addr_max, addr_max - 1);
+	}
 
 	pernet->addrs--;
 	list_del_rcu(&entry->list);
@@ -956,9 +966,9 @@ static void __flush_addrs(struct net *net, struct list_head *list)
 
 static void __reset_counters(struct pm_nl_pernet *pernet)
 {
-	pernet->add_addr_signal_max = 0;
-	pernet->add_addr_accept_max = 0;
-	pernet->local_addr_max = 0;
+	WRITE_ONCE(pernet->add_addr_signal_max, 0);
+	WRITE_ONCE(pernet->add_addr_accept_max, 0);
+	WRITE_ONCE(pernet->local_addr_max, 0);
 	pernet->addrs = 0;
 }