[PATCH net-next 03/10] mptcp: skip to next candidate if subflow has unacked data

[Mat Martineau <mathew.j.martineau@linux.intel.com>]

From: Florian Westphal <fw@strlen.de>

In case a subflow path is blocked, MPTCP-level retransmit may not take
place anymore because such subflow is likely to have unacked data left
in its write queue.

Ignore subflows that have experienced loss and test next candidate.

Fixes: 3b1d6210a95773691 ("mptcp: implement and use MPTCP-level retransmission")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
---
 net/mptcp/protocol.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index a46a542b1766..806c0658e42f 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1725,8 +1725,11 @@ static struct sock *mptcp_subflow_get_retrans(const struct mptcp_sock *msk)
 			continue;
 
 		/* still data outstanding at TCP level?  Don't retransmit. */
-		if (!tcp_write_queue_empty(ssk))
+		if (!tcp_write_queue_empty(ssk)) {
+			if (inet_csk(ssk)->icsk_ca_state >= TCP_CA_Loss)
+				continue;
 			return NULL;
+		}
 
 		if (subflow->backup) {
 			if (!backup)
-- 
2.29.2