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From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 24 May 2022 15:13:29 -0700
Message-ID: <CANn89i+R9RgmD=AQ4vX1Vb_SQAj4c3fi7-ZtQz-inYY4Sq4CMQ@mail.gmail.com>
Subject: Re: [RFC] EADDRINUSE from bind() on application restart after killing
To:     Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "open list:NETWORKING [TCP]" <netdev@vger.kernel.org>,
        Gabriel Krisman Bertazi <krisman@collabora.com>,
        open list <linux-kernel@vger.kernel.org>
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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;
        }