netdev - Re: [PATCH net-next 3/3] tcp: add a fast path in tcp_delack

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Message-ID: <CANn89i+8myPgn61bn7DBqcnK5kXX2XvPo2oc2TfzntPUkeqQ6w@mail.gmail.com>
Date: Thu, 3 Oct 2024 11:11:14 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com
Subject: Re: [PATCH net-next 3/3] tcp: add a fast path in tcp_delack_timer()

On Thu, Oct 3, 2024 at 1:19 AM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> Hello Eric,
>
        !READ_ONCE(tcp_sk(sk)->compressed_ack))
>
> I wonder what the use of single READ_ONCE() is here without a
> WRITE_ONCE() pair? It cannot guarantee that the result of reading
> compressed_ack is accurate. What if we use without this READ_ONCE()
> here?

Have you read the changelog and comments about this 'accuracy' thing ?

If you do not use the READ_ONCE() here, only concern is KCSAN might
trigger a splat.

The WRITE_ONCE() for a single byte is not needed, no tearing is possible.