This patch refactors __mptcp_subflow_push_pending logic from:

For each dfrag:
	While sends succeed:
		Call the scheduler (selects subflow and msk->snd_burst)
		Send the dfrag data with mptcp_subflow_delegate(), break
		Send the dfrag data with mptcp_sendmsg_frag()
		Update dfrag->already_sent, msk->snd_nxt, msk->snd_burst
	Update msk->first_pending

to:

While first_pending isn't empty:
	Call the scheduler (selects subflow and msk->snd_burst)
	Send the dfrag data with mptcp_subflow_delegate(), break
	Send the dfrag data with mptcp_sendmsg_frag()
	For each pending dfrag:
		While sends succeed:
			Send the dfrag data with mptcp_sendmsg_frag()
			Update already_sent, snd_nxt, snd_burst
		Update msk->first_pending
		Break if required by msk->snd_burst / etc

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/protocol.c | 66 +++++++++++++++++++++++---------------------
 1 file changed, 34 insertions(+), 32 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index a8674b431593..c036a788fc27 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1602,44 +1602,46 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk,
 	int len, copied = 0;
 
 	info.flags = 0;
-	while ((dfrag = mptcp_send_head(sk))) {
-		info.sent = dfrag->already_sent;
-		info.limit = dfrag->data_len;
-		len = dfrag->data_len - dfrag->already_sent;
-		while (len > 0) {
-			int ret = 0;
+	while (mptcp_send_head(sk)) {
+		/* check for a different subflow usage only after
+		 * spooling the first chunk of data
+		 */
+		xmit_ssk = first ? ssk : mptcp_subflow_get_send(msk);
+		if (!xmit_ssk)
+			goto out;
+		if (xmit_ssk != ssk) {
+			mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk),
+					       MPTCP_DELEGATE_SEND);
+			goto out;
+		}
 
-			/* check for a different subflow usage only after
-			 * spooling the first chunk of data
-			 */
-			xmit_ssk = first ? ssk : mptcp_subflow_get_send(msk);
-			if (!xmit_ssk)
-				goto out;
-			if (xmit_ssk != ssk) {
-				mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk),
-						       MPTCP_DELEGATE_SEND);
-				goto out;
-			}
+		while ((dfrag = mptcp_send_head(sk))) {
+			info.sent = dfrag->already_sent;
+			info.limit = dfrag->data_len;
+			len = dfrag->data_len - dfrag->already_sent;
+			while (len > 0) {
+				int ret = 0;
 
-			ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
-			if (ret <= 0)
-				goto out;
+				ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
+				if (ret <= 0)
+					goto out;
 
-			info.sent += ret;
-			copied += ret;
-			len -= ret;
-			first = false;
+				info.sent += ret;
+				copied += ret;
+				len -= ret;
+				first = false;
 
-			mptcp_update_post_push(msk, dfrag, ret);
-		}
-		WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
+				mptcp_update_post_push(msk, dfrag, ret);
+			}
+			WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
 
-		if (msk->snd_burst <= 0 ||
-		    !sk_stream_memory_free(ssk) ||
-		    !mptcp_subflow_active(mptcp_subflow_ctx(ssk))) {
-			goto out;
+			if (msk->snd_burst <= 0 ||
+			    !sk_stream_memory_free(ssk) ||
+			    !mptcp_subflow_active(mptcp_subflow_ctx(ssk))) {
+				goto out;
+			}
+			mptcp_set_timeout(sk);
 		}
-		mptcp_set_timeout(sk);
 	}
 
 out:
-- 
2.35.3