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SubjectRe: [PATCH v4] tcp: fix tcp_init_transfer() to not reset icsk_ca_initialized
On Sat, Jul 3, 2021 at 5:49 PM David Miller <davem@davemloft.net> wrote:
>
> From: Nguyen Dinh Phi <phind.uet@gmail.com>
> Date: Sat, 3 Jul 2021 17:34:17 +0800
>
> > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > index 7d5e59f688de..855ada2be25e 100644
> > --- a/net/ipv4/tcp_input.c
> > +++ b/net/ipv4/tcp_input.c
> > @@ -5922,7 +5922,6 @@ void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb)
> > tp->snd_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
> > tp->snd_cwnd_stamp = tcp_jiffies32;
> >
> > - icsk->icsk_ca_initialized = 0;
> > bpf_skops_established(sk, bpf_op, skb);
> > if (!icsk->icsk_ca_initialized)
> > tcp_init_congestion_control(sk);
>
> Don't you have to make the tcp_init_congestion_control() call unconditional now?

I think we want to keep it conditional, to avoid double-initialization
if the BPF code sets the congestion control algorithm and initializes
it. But that's relatively new and subtle, so it might be nice for this
patch to add a comment about that, since it's touching this part of
the code anyway:

- icsk->icsk_ca_initialized = 0;
bpf_skops_established(sk, bpf_op, skb);
+ /* Initialize congestion control unless BPF initialized it already: */
if (!icsk->icsk_ca_initialized)
tcp_init_congestion_control(sk);

neal

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