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Date:   Mon, 24 Oct 2022 18:20:18 +0000
To:     Neal Cardwell <>
Subject: Re: [PATCH net] tcp: fix indefinite deferral of RTO with SACK reneging


This patch was applied to netdev/net.git (master)
by Jakub Kicinski <>:

On Fri, 21 Oct 2022 17:08:21 +0000 you wrote:
> From: Neal Cardwell <>
> This commit fixes a bug that can cause a TCP data sender to repeatedly
> defer RTOs when encountering SACK reneging.
> The bug is that when we're in fast recovery in a scenario with SACK
> reneging, every time we get an ACK we call tcp_check_sack_reneging()
> and it can note the apparent SACK reneging and rearm the RTO timer for
> srtt/2 into the future. In some SACK reneging scenarios that can
> happen repeatedly until the receive window fills up, at which point
> the sender can't send any more, the ACKs stop arriving, and the RTO
> fires at srtt/2 after the last ACK. But that can take far too long
> (O(10 secs)), since the connection is stuck in fast recovery with a
> low cwnd that cannot grow beyond ssthresh, even if more bandwidth is
> available.
> [...]

Here is the summary with links:
  - [net] tcp: fix indefinite deferral of RTO with SACK reneging

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