pppd stuck in dialing process

i'm connecting several usb modems to my Ubuntu:

uname -a

Linux devlp 2.6.32-28-generic #55-Ubuntu SMP Mon Jan 10 21:21:01 UTC 2011 i686 GNU/Linux

pppd version: 2.4.5

i'm doing a test with 8 sierra wireless modems, and all of them are connected and work. each of them has a "ppp" interface.

after they are connected, i'm trying to reconnect ppp7, and at first, pppd fails, then in the second try it reaches the point where it says: "Se开发者_运维百科rial connection established" and stuck. i tried all kill signals to kill that pppd without success, and the only way to terminate it is to plug-out the modem it tried to dial.

i looked for the exact place where the pppd get stuck and it's right over here:

int generic_establish_ppp (int fd)
{
    int x;

    if (new_style_driver) {
        int flags;
        FILE *f=fopen("/root/ptest.log","a");
        fputs("before get channel\n",f);
        fflush(f);
        /* Open an instance of /dev/ppp and connect the channel to it */
        if (ioctl(fd, PPPIOCGCHAN, &chindex) == -1) { // <<<<<<< STUCK HERE
            error("Couldn't get channel number: %m");
            goto err;
        }
        fputs("after get channel\n",f);
        ....
    }
}

it looks like the problem is specifically with ppp7 - and it can be any modem so i don't think it's a modem problem, but what i don't understand is what really happens in that command? who is responsible for the answer? is it only the kernel? the modem driver? the modem itself? i don't quite understand what to do with that information since PPPIOCGCHAN documentation is very poor..

i thought at first that maybe pppd is not releasing the channel or ppp after disconnect so i compiled my own pppd version and added PPPIOCDISCONN and PPPIOCDETACH just to make sure my version is fine with that, and the results were the same.

what you think?

well i'm pretty i solved this one - I've added some lines in pppd before the ioctl command to make fd NONBLOCK :)