From: Gang Yan <yangang@kylinos.cn>

The original condition would stop moving skbs or spooling backlog even
when the receive queue is empty, leading to receive stall.

Modify the condition in __mptcp_move_skbs() and mptcp_can_spool_backlog()
to only treat rcvbuf as full when:
  sk_rmem_alloc_get(sk) > sk->sk_rcvbuf && !skb_queue_empty(&sk->sk_receive_queue)

This ensures the backlog can still be moved to the receive queue when
the queue is empty, avoiding stall problems.

Fixes: 6228efe0cc01 ("mptcp: leverage the backlog for RX packet processing")
Co-developed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Gang Yan <yangang@kylinos.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 759f0486c40b..b1915eef4dcf 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2204,7 +2204,8 @@ static bool __mptcp_move_skbs(struct sock *sk, struct list_head *skbs, u32 *delt
 	*delta = 0;
 	while (1) {
 		/* If the msk recvbuf is full stop, don't drop */
-		if (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
+		if (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf &&
+		    !skb_queue_empty(&sk->sk_receive_queue))
 			break;
 
 		prefetch(skb->next);
@@ -2259,7 +2260,8 @@ static bool mptcp_can_spool_backlog(struct sock *sk, struct list_head *skbs)
 
 	/* Don't spool the backlog if the rcvbuf is full. */
 	if (RB_EMPTY_ROOT(&msk->backlog_queue) ||
-	    sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
+	    (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf &&
+	     !skb_queue_empty(&sk->sk_receive_queue)))
 		return false;
 
 	INIT_LIST_HEAD(skbs);
-- 
2.43.0