netdev - Re: [PATCH net-next 1/2] tcp: tcp_tx_timestamp() must look at the rtx queue

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Message-ID: <CAL+tcoB6RXXxL4f2hrbWq8gHX6=7VOY3c2+VLXiumewUefR11A@mail.gmail.com>
Date: Wed, 28 Jan 2026 10:22:13 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Neal Cardwell <ncardwell@...gle.com>, Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next 1/2] tcp: tcp_tx_timestamp() must look at the rtx queue

On Tue, Jan 27, 2026 at 8:38 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> tcp_tx_timestamp() is only called at the end of tcp_sendmsg_locked()
> before the final tcp_push().
>
> By the time it is called, it is possible all the copied data
> has been sent already (transmit queue is empty).
>
> If this is the case, use the last skb in the rtx queue.
>
> Fixes: 75c119afe14f ("tcp: implement rb-tree based retransmit queue")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Jason Xing <kerneljasonxing@...il.com>

Great, I failed to spot this case... It could be reproduced when
'wait_for_space' is triggered. I strongly feel that more packetdrill
tests are needed to observe the behavior of socket timestamping.

+ Willem

Thanks,
Jason