So that we can skip already used endpoint at local address
selection time.
This allows for fair local endpoints usage in case of subflow
failure.

As a side effect, this patch also enforces that each endpoint
is used at most once for each mptcp connection.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/pm.c         | 1 +
 net/mptcp/pm_netlink.c | 8 +++++++-
 net/mptcp/protocol.h   | 1 +
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index 761995a34124..1ff856dd92c4 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -376,6 +376,7 @@ void mptcp_pm_data_reset(struct mptcp_sock *msk)
 	WRITE_ONCE(msk->pm.accept_subflow, false);
 	WRITE_ONCE(msk->pm.remote_deny_join_id0, false);
 	msk->pm.status = 0;
+	bitmap_zero(msk->pm.endpoint_usage_mask, 256);
 
 	mptcp_pm_nl_data_init(msk);
 }
diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 3186d33b5208..78b68a8216b6 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -173,6 +173,9 @@ select_local_address(const struct pm_nl_pernet *pernet,
 		if (!(entry->flags & MPTCP_PM_ADDR_FLAG_SUBFLOW))
 			continue;
 
+		if (test_bit(entry->addr.id, msk->pm.endpoint_usage_mask))
+			continue;
+
 		if (entry->addr.family != sk->sk_family) {
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 			if ((entry->addr.family == AF_INET &&
@@ -512,8 +515,10 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 			check_work_pending(msk);
 			nr = fill_remote_addresses_vec(msk, fullmesh, addrs);
 			spin_unlock_bh(&msk->pm.lock);
-			for (i = 0; i < nr; i++)
+			for (i = 0; i < nr; i++) {
+				set_bit(local->addr.id, msk->pm.endpoint_usage_mask);
 				__mptcp_subflow_connect(sk, &local->addr, &addrs[i]);
+			}
 			spin_lock_bh(&msk->pm.lock);
 			return;
 		}
@@ -1282,6 +1287,7 @@ static int mptcp_nl_remove_subflow_and_signal_addr(struct net *net,
 		mptcp_pm_remove_anno_addr(msk, addr, remove_subflow);
 		if (remove_subflow)
 			mptcp_pm_remove_subflow(msk, &list);
+		clear_bit(addr->id, msk->pm.endpoint_usage_mask);
 		release_sock(sk);
 
 next:
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index a6a4bd7de5b4..d384f285b6c1 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -190,6 +190,7 @@ struct mptcp_pm_data {
 
 	spinlock_t	lock;		/*protects the whole PM data */
 
+	DECLARE_BITMAP(endpoint_usage_mask, 256);
 	u8		addr_signal;
 	bool		server_side;
 	bool		work_pending;
-- 
2.33.1