netdev - RE: [RFC PATCH bpf-next 0/8] Socket migration for SO

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Date:   Wed, 18 Nov 2020 09:18:24 +0000
From:   David Laight <David.Laight@...LAB.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" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH bpf-next 0/8] Socket migration for SO_REUSEPORT.

From: Kuniyuki Iwashima
> Sent: 17 November 2020 09:40
> 
> 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.

Can't you do something to stop new connections being queued (like
setting the 'backlog' to zero), then carry on doing accept()s
for a guard time (or until the queue length is zero) before finally
closing the listening socket.

	David

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