Merge branch 'mptcp-pm-lockless-list-traversal-and-cleanup'

Matthieu Baerts says:

====================
mptcp: pm: lockless list traversal and cleanup

Here are two patches improving the MPTCP in-kernel path-manager.

- Patch 1: the get and dump endpoints operations are iterating over the
  endpoints list in a lockless way.

- Patch 2: reduce the code duplication to lookup an endpoint.
====================

Link: https://patch.msgid.link/20241115-net-next-mptcp-pm-lockless-dump-v1-0-f4a1bcb4ca2c@kernel.org
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

net/mptcp/pm_netlink.c

@@ -512,7 +512,8 @@ __lookup_addr_by_id(struct pm_nl_pernet *pernet, unsigned int id)
 {
 	struct mptcp_pm_addr_entry *entry;
 
-	list_for_each_entry(entry, &pernet->local_addr_list, list) {
+	list_for_each_entry_rcu(entry, &pernet->local_addr_list, list,
+				lockdep_is_held(&pernet->lock)) {
 		if (entry->addr.id == id)
 			return entry;
 	}
@@ -1142,17 +1143,13 @@ int mptcp_pm_nl_get_local_id(struct mptcp_sock *msk, struct mptcp_addr_info *skc
 {
 	struct mptcp_pm_addr_entry *entry;
 	struct pm_nl_pernet *pernet;
-	int ret = -1;
+	int ret;
 
 	pernet = pm_nl_get_pernet_from_msk(msk);
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(entry, &pernet->local_addr_list, list) {
-		if (mptcp_addresses_equal(&entry->addr, skc, entry->addr.port)) {
-			ret = entry->addr.id;
-			break;
-		}
-	}
+	entry = __lookup_addr(pernet, skc);
+	ret = entry ? entry->addr.id : -1;
 	rcu_read_unlock();
 	if (ret >= 0)
 		return ret;
@@ -1179,15 +1176,11 @@ bool mptcp_pm_nl_is_backup(struct mptcp_sock *msk, struct mptcp_addr_info *skc)
 {
 	struct pm_nl_pernet *pernet = pm_nl_get_pernet_from_msk(msk);
 	struct mptcp_pm_addr_entry *entry;
-	bool backup = false;
+	bool backup;
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(entry, &pernet->local_addr_list, list) {
-		if (mptcp_addresses_equal(&entry->addr, skc, entry->addr.port)) {
-			backup = !!(entry->flags & MPTCP_PM_ADDR_FLAG_BACKUP);
-			break;
-		}
-	}
+	entry = __lookup_addr(pernet, skc);
+	backup = entry && !!(entry->flags & MPTCP_PM_ADDR_FLAG_BACKUP);
 	rcu_read_unlock();
 
 	return backup;
@@ -1824,7 +1817,7 @@ int mptcp_pm_nl_get_addr(struct sk_buff *skb, struct genl_info *info)
 		goto fail;
 	}
 
-	spin_lock_bh(&pernet->lock);
+	rcu_read_lock();
 	entry = __lookup_addr_by_id(pernet, addr.addr.id);
 	if (!entry) {
 		GENL_SET_ERR_MSG(info, "address not found");
@@ -1838,11 +1831,11 @@ int mptcp_pm_nl_get_addr(struct sk_buff *skb, struct genl_info *info)
 
 	genlmsg_end(msg, reply);
 	ret = genlmsg_reply(msg, info);
-	spin_unlock_bh(&pernet->lock);
+	rcu_read_unlock();
 	return ret;
 
 unlock_fail:
-	spin_unlock_bh(&pernet->lock);
+	rcu_read_unlock();
 
 fail:
 	nlmsg_free(msg);
@@ -1866,7 +1859,7 @@ int mptcp_pm_nl_dump_addr(struct sk_buff *msg,
 
 	pernet = pm_nl_get_pernet(net);
 
-	spin_lock_bh(&pernet->lock);
+	rcu_read_lock();
 	for (i = id; i < MPTCP_PM_MAX_ADDR_ID + 1; i++) {
 		if (test_bit(i, pernet->id_bitmap)) {
 			entry = __lookup_addr_by_id(pernet, i);
@@ -1891,7 +1884,7 @@ int mptcp_pm_nl_dump_addr(struct sk_buff *msg,
 			genlmsg_end(msg, hdr);
 		}
 	}
-	spin_unlock_bh(&pernet->lock);
+	rcu_read_unlock();
 
 	cb->args[0] = id;
 	return msg->len;