Re: [PATCH v4] tcp: fix tcp_init_transfer() to not reset icsk_ca_initialized

On Sat, Jul 3, 2021 at 5:49 PM David Miller [off-list ref] wrote:

From: Nguyen Dinh Phi <redacted>
Date: Sat,  3 Jul 2021 17:34:17 +0800

quoted

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