netdev - [PATCH net-next v2] tcp: fix condition for increasing pingpong count

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Date:   Wed, 20 Jul 2022 15:24:04 +0800
From:   LemmyHuang <hlm3280@....com>
To:     edumazet@...gle.com, davem@...emloft.net, dsahern@...nel.org,
        kuba@...nel.org, pabeni@...hat.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        LemmyHuang <hlm3280@....com>
Subject: [PATCH net-next v2] tcp: fix condition for increasing pingpong count

When CONFIG_HZ defaults to 1000Hz and the network transmission time is
less than 1ms, lsndtime and lrcvtime are likely to be equal, which will
lead to hundreds of interactions before entering pingpong mode.

Fixes: 4a41f453bedf ("tcp: change pingpong threshold to 3")
Suggested-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: LemmyHuang <hlm3280@....com>
---
v2:
  * Use !after() wrapping the values. (Jakub Kicinski)

v1: https://lore.kernel.org/netdev/20220719130136.11907-1-hlm3280@163.com/
---
 net/ipv4/tcp_output.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 858a15cc2..c1c95dc40 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -172,7 +172,7 @@ static void tcp_event_data_sent(struct tcp_sock *tp,
 	 * and it is a reply for ato after last received packet,
 	 * increase pingpong count.
 	 */
-	if (before(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&
+	if (!after(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&
 	    (u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
 		inet_csk_inc_pingpong_cnt(sk);
 
-- 
2.27.0