[PATCH export v3 3/4] mptcp: reset subflow on MP_FAIL when OoO queue is non-empty

[Chenguang Zhao <chenguang.zhao@linux.dev>]

From: Chenguang Zhao <zhaochenguang@kylinos.cn>

Infinite mapping needs contiguous data. If the MPTCP OoO queue is not
empty, reset the subflow instead of falling back.

Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
---
 net/mptcp/pm.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index ba7c6f80a183..8c263084db7b 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -882,6 +882,16 @@ void mptcp_pm_mp_fail_received(struct sock *sk, u64 fail_seq)
 		spin_unlock_bh(&msk->fallback_lock);
 		return;
 	}
+
+	/* RFC8684 §3.7: Infinite mapping requires contiguous data */
+	if (!subflow->fail_tout &&
+	    !RB_EMPTY_ROOT(&msk->out_of_order_queue)) {
+		spin_unlock_bh(&msk->fallback_lock);
+		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_FALLBACKFAILED);
+		mptcp_subflow_reset(sk);
+		return;
+	}
+
 	msk->allow_subflows = false;
 	spin_unlock_bh(&msk->fallback_lock);
 
-- 
2.25.1