From: David Laight <David.Laight@xxxxxxxxxx> Date: Wed, 18 Nov 2020 09:18:24 +0000 > 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. Yes, but with eBPF. There are some ideas suggested and well discussed in the thread below, resulting in that connection draining by eBPF was merged. https://lore.kernel.org/netdev/1443313848-751-1-git-send-email-tolga.ceylan@xxxxxxxxx/ Also, setting zero to backlog does not work well. https://lore.kernel.org/netdev/1447262610.17135.114.camel@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ ---8<--- From: Eric Dumazet <eric.dumazet@xxxxxxxxx> Subject: Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN_OFF socket option as drain mode Date: Wed, 11 Nov 2015 09:23:30 -0800 > Actually listen(fd, 0) is not going to work well : > > For request_sock that were created (by incoming SYN packet) before this > listen(fd, 0) call, the 3rd packet (ACK coming from client) would not be > able to create a child attached to this listener. > > sk_acceptq_is_full() test in tcp_v4_syn_recv_sock() would simply drop > the thing. ---8<---
