[PATCH v2] mptcp: ensure there is unacked data at all subflow

[Yonglong Li <liyonglong@chinatelecom.cn>]

MPTCP-level retransmit may take place if first subflow
without data in its write queue and second subflow is likely to
have unacked data left in its write queue. In this condition data
maybe double retransmited.

Signed-off-by: Yonglong Li <liyonglong@chinatelecom.cn>
---
 net/mptcp/protocol.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 9d7e7e1..66707ab 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2072,6 +2072,7 @@ static struct sock *mptcp_subflow_get_retrans(const struct mptcp_sock *msk)
 {
 	struct mptcp_subflow_context *subflow;
 	struct sock *backup = NULL;
+	struct sock *idle = NULL;
 
 	sock_owned_by_me((const struct sock *)msk);
 
@@ -2097,10 +2098,11 @@ static struct sock *mptcp_subflow_get_retrans(const struct mptcp_sock *msk)
 			continue;
 		}
 
-		return ssk;
+		if (!idle)
+			idle = ssk;
 	}
 
-	return backup;
+	return idle ? : backup;
 }
 
 static void mptcp_dispose_initial_subflow(struct mptcp_sock *msk)
-- 
1.8.3.1