netdev - [PATCH net] tcp: avoid too many retransmit packets

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Message-ID: <20240710221826.32571-1-kuniyu@amazon.com>
Date: Wed, 10 Jul 2024 15:18:26 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <eric.dumazet@...il.com>, <jmaxwell37@...il.com>,
	<kuba@...nel.org>, <kuniyu@...zon.com>, <ncardwell@...gle.com>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: [PATCH net] tcp: avoid too many retransmit packets

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 10 Jul 2024 00:14:01 +0000
> If a TCP socket is using TCP_USER_TIMEOUT, and the other peer
> retracted its window to zero, tcp_retransmit_timer() can
> retransmit a packet every two jiffies (2 ms for HZ=1000),
> for about 4 minutes after TCP_USER_TIMEOUT has 'expired'.
> 
> The fix is to make sure tcp_rtx_probe0_timed_out() takes
> icsk->icsk_user_timeout into account.
> 
> Before blamed commit, the socket would not timeout after
> icsk->icsk_user_timeout, but would use standard exponential
> backoff for the retransmits.
> 
> Also worth noting that before commit e89688e3e978 ("net: tcp:
> fix unexcepted socket die when snd_wnd is 0"), the issue
> would last 2 minutes instead of 4.
> 
> Fixes: b701a99e431d ("tcp: Add tcp_clamp_rto_to_user_timeout() helper to improve accuracy")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>