linux-kernel - [PATCH net-next 2/3] net: tcp: allow zero-window ACK update the window

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Message-Id: <20230727125125.1194376-3-imagedong@tencent.com>
Date:   Thu, 27 Jul 2023 20:51:24 +0800
From:   menglong8.dong@...il.com
To:     edumazet@...gle.com
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        dsahern@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Menglong Dong <imagedong@...cent.com>
Subject: [PATCH net-next 2/3] net: tcp: allow zero-window ACK update the window

From: Menglong Dong <imagedong@...cent.com>

Fow now, an ACK can update the window in following case, according to
the tcp_may_update_window():

1. the ACK acknowledged new data
2. the ACK has new data
3. the ACK expand the window and the seq of it is valid

Now, we allow the ACK update the window if the window is 0, and the
seq/ack of it is valid. This is for the case that the receiver replies
an zero-window ACK when it is under memory stress and can't queue the new
data.

Signed-off-by: Menglong Dong <imagedong@...cent.com>
---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 03111af6115d..d13b89370f76 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3526,7 +3526,7 @@ static inline bool tcp_may_update_window(const struct tcp_sock *tp,
 {
 	return	after(ack, tp->snd_una) ||
 		after(ack_seq, tp->snd_wl1) ||
-		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
+		(ack_seq == tp->snd_wl1 && (nwin > tp->snd_wnd || !nwin));
 }
 
 /* If we update tp->snd_una, also update tp->bytes_acked */
-- 
2.40.1