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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