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SubjectRe: [RFC] EADDRINUSE from bind() on application restart after killing
On Tue, May 24, 2022 at 1:19 AM Muhammad Usama Anjum
<usama.anjum@collabora.com> wrote:
>
> Hello,
>
> We have a set of processes which talk with each other through a local
> TCP socket. If the process(es) are killed (through SIGKILL) and
> restarted at once, the bind() fails with EADDRINUSE error. This error
> only appears if application is restarted at once without waiting for 60
> seconds or more. It seems that there is some timeout of 60 seconds for
> which the previous TCP connection remains alive waiting to get closed
> completely. In that duration if we try to connect again, we get the error.
>
> We are able to avoid this error by adding SO_REUSEADDR attribute to the
> socket in a hack. But this hack cannot be added to the application
> process as we don't own it.
>
> I've looked at the TCP connection states after killing processes in
> different ways. The TCP connection ends up in 2 different states with
> timeouts:
>
> (1) Timeout associated with FIN_WAIT_1 state which is set through
> `tcp_fin_timeout` in procfs (60 seconds by default)
>
> (2) Timeout associated with TIME_WAIT state which cannot be changed. It
> seems like this timeout has come from RFC 1337.
>
> The timeout in (1) can be changed. Timeout in (2) cannot be changed. It
> also doesn't seem feasible to change the timeout of TIME_WAIT state as
> the RFC mentions several hazards. But we are talking about a local TCP
> connection where maybe those hazards aren't applicable directly? Is it
> possible to change timeout for TIME_WAIT state for only local
> connections without any hazards?
>
> We have tested a hack where we replace timeout of TIME_WAIT state from a
> value in procfs for local connections. This solves our problem and
> application starts to work without any modifications to it.
>
> The question is that what can be the best possible solution here? Any
> thoughts will be very helpful.
>

One solution would be to extend TCP diag to support killing TIME_WAIT sockets.
(This has been raised recently anyway)

Then you could zap all sockets, before re-starting your program.

ss -K -ta src :listen_port

Untested patch:

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9984d23a7f3e1353d2e1fc9053d98c77268c577e..1b7bde889096aa800b2994c64a3a68edf3b62434
100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4519,6 +4519,15 @@ int tcp_abort(struct sock *sk, int err)
local_bh_enable();
return 0;
}
+ if (sk->sk_state == TCP_TIME_WAIT) {
+ struct inet_timewait_sock *tw = inet_twsk(sk);
+
+ refcount_inc(&tw->tw_refcnt);
+ local_bh_disable();
+ inet_twsk_deschedule_put(tw);
+ local_bh_enable();
+ return 0;
+ }
return -EOPNOTSUPP;
}
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