linux-kernel - Re: [RFC PATCH bpf-next 0/8] Socket migration for SO

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Date:   Wed, 18 Nov 2020 17:25:44 +0100
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Benjamin Herrenschmidt <benh@...zon.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH bpf-next 0/8] Socket migration for SO_REUSEPORT.



On 11/17/20 10:40 AM, Kuniyuki Iwashima wrote:
> The SO_REUSEPORT option allows sockets to listen on the same port and to
> accept connections evenly. However, there is a defect in the current
> implementation. When a SYN packet is received, the connection is tied to a
> listening socket. Accordingly, when the listener is closed, in-flight
> requests during the three-way handshake and child sockets in the accept
> queue are dropped even if other listeners could accept such connections.
> 
> This situation can happen when various server management tools restart
> server (such as nginx) processes. For instance, when we change nginx
> configurations and restart it, it spins up new workers that respect the new
> configuration and closes all listeners on the old workers, resulting in
> in-flight ACK of 3WHS is responded by RST.
> 

I know some programs are simply removing a listener from the group,
so that they no longer handle new SYN packets,
and wait until all timers or 3WHS have completed before closing them.

They pass fd of newly accepted children to more recent programs using af_unix fd passing,
while in this draining mode.

Quite frankly, mixing eBPF in the picture is distracting.

It seems you want some way to transfer request sockets (and/or not yet accepted established ones)
from fd1 to fd2, isn't it something that should be discussed independently ?