Re: [PATCH net v2] tcp: avoid creating multiple req socks with the same tuples

[Eric Dumazet]

On 6/13/19 9:19 PM, maowenan wrote:
> 
> 
> @Eric, for this issue I only want to check TCP_NEW_SYN_RECV sk, is it OK like below?
>  +       if (!osk && sk->sk_state == TCP_NEW_SYN_RECV)
>  +               reqsk = __inet_lookup_established(sock_net(sk), &tcp_hashinfo,
>  +                                                       sk->sk_daddr, sk->sk_dport,
>  +                                                       sk->sk_rcv_saddr, sk->sk_num,
>  +                                                       sk->sk_bound_dev_if, sk->sk_bound_dev_if);
>  +       if (unlikely(reqsk)) {
> 

Not enough.

If we have many cpus here, there is a chance another cpu has inserted a request socket, then
replaced it by an ESTABLISH socket for the same 4-tuple.

We need to take the per bucket spinlock much sooner.

And this is fine, all what matters is that we do no longer grab the listener spinlock.