From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Yurij M. Plotnikov" <Yurij.Plotnikov@oktetlabs.ru>
Subject: Connect hangs for a while before returns -1 with ECONNREFUSED on
 3.2 for loopback
Date: Fri, 03 Feb 2012 10:25:53 +0400
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On kernel 3.2.0-0.bpo.1-amd64 I see some strange behaviour of connect() 
in case of connection via loopback. Lets see the following steps (there 
are two processes on the host, and the first one with two threads)

Thread1:
1. socket(PF_INET, SOCK_STREAM, 0) ->  3
2. bind(10.27.10.1:26820) ->  0 /* The address is bound to some interface, eth1 */
3. listen(3, 1) ->  0

sleep for a while

Thread2:
4. shutdown(3, SHUT_RD) ->  0

sleep for a while

Another process:
5. socket(PF_INET, SOCK_STREAM, 0) ->  4
6. connect(4, 10.27.10.1:26820)

connect() returns -1 with ECONNREFUSED but after some time. In case of 
two peer hosts connect() returns -1 with ECONNREFUSED almost 
immediately, so does for the other kernel versions.

In attachment c program to reproduce this problem.

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 name="connect_loopback.c"
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 filename="connect_loopback.c"

#include <unistd.h>
#include <stdio.h>
#include <netinet/in.h>
#include <errno.h>

main()
{
    int child_sock;
    int sock;
    struct sockaddr_in addr;
    int rc;
    int proc;

    sock = socket(PF_INET, SOCK_STREAM, 0);
    printf("socket() -> %d(%d)\n", sock, errno);

    addr.sin_family = AF_INET;
    addr.sin_port = htons(12345);
    addr.sin_addr.s_addr = inet_addr("10.0.1.1");
    rc = bind(sock, (struct sockaddr *)&addr, sizeof(addr));
    printf("bind() -> %d(%d)\n", rc, errno);

    rc = listen(sock, 1);
    printf("listen() -> %d(%d)\n", rc, errno);

    sleep(1);

    rc = shutdown(sock, SHUT_RD);
    printf("shutdown() -> %d(%d)\n", rc, errno);

    proc = fork();
    if (proc)
    {
        child_sock = socket(PF_INET, SOCK_STREAM, 0);
        printf("Child: socket() -> %d(%d)\n", child_sock, errno);
        rc = connect(child_sock, (struct sockaddr *)&addr, sizeof(addr));
        printf("connect() -> %d(%d)\n", rc, errno);
    }
    else
    {
        printf("Waiting...\n");getchar();
    }

    return 0;
}

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