linux-kernel - Re: [PATCH v4] tcp: fix tcp_init_transfer() to not reset icsk_ca

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Date:   Tue, 6 Jul 2021 00:34:47 +0800
From:   Phi Nguyen <phind.uet@...il.com>
To:     Neal Cardwell <ncardwell@...gle.com>,
        David Miller <davem@...emloft.net>
Cc:     yhs@...com, edumazet@...gle.com, yoshfuji@...ux-ipv6.org,
        dsahern@...nel.org, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, kafai@...com,
        songliubraving@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, ycheng@...gle.com, yyd@...gle.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+f1e24a0594d4e3a895d3@...kaller.appspotmail.com
Subject: Re: [PATCH v4] tcp: fix tcp_init_transfer() to not reset
 icsk_ca_initialized

On 7/4/2021 9:52 PM, Neal Cardwell wrote:
> 
> 
> On Sat, Jul 3, 2021 at 5:49 PM David Miller <davem@...emloft.net 
> <mailto:davem@...emloft.net>> wrote:
>  >
>  > From: Nguyen Dinh Phi <phind.uet@...il.com <mailto:phind.uet@...il.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 a BPF op initialized it 
> already: */
>          if (!icsk->icsk_ca_initialized)
>                  tcp_init_congestion_control(sk);
> 
> neal
> 
I will make a new version with your comment.
Thank you very much for helping.