netdev - Re: [PATCH bpf-next 1/2] bpf, net: Support SO_REUSEPORT sockets with bpf_sk

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Date: Fri, 26 May 2023 14:08:48 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
 daniel@...earbox.net, davem@...emloft.net, dsahern@...nel.org,
 edumazet@...gle.com, haoluo@...gle.com, joe@...ium.io, joe@...d.net.nz,
 john.fastabend@...il.com, jolsa@...nel.org, kafai@...com,
 kpsingh@...nel.org, kuba@...nel.org, linux-kernel@...r.kernel.org,
 lmb@...valent.com, netdev@...r.kernel.org, pabeni@...hat.com,
 sdf@...gle.com, song@...nel.org, willemdebruijn.kernel@...il.com, yhs@...com
Subject: Re: [PATCH bpf-next 1/2] bpf, net: Support SO_REUSEPORT sockets with
 bpf_sk_assign

On 5/25/23 7:49 PM, Kuniyuki Iwashima wrote:
>> We may want to use rcu_access_pointer(sk->sk_reuseport_cb) in
>> each lookup_reuseport() instead of adding sk_state check ?

> And if someone has a weird program that creates multiple listeners and
> disable SO_REUSEPORT for a listener that hits first in lhash2, checking
> sk_reuseport_cb might not work ?  

I am also not sure what the correct expectation is if the application disable 
SO_REUSEPORT in a sk after bind(). This is not something new or specific from 
the current patch though.

> I hope no one does such though, checking sk_reuseport 
> and sk_state could be better.

My previous comment on checking sk_state is to avoid the unnecessary 
inet_ehashfn() for the TCP_ESTABLISHED sk. Checking sk_reuseport_cb could also 
work since it should be NULL for established sk. However, not sure if it could 
be another cacheline access. The udp one is checking the sk_state also: 
"sk->sk_reuseport && sk->sk_state != TCP_ESTABLISHED".