Description of Problem:
I'm experiencing problems after upgrading from Redhat 7.2 (kernel 2.4.9) to 7.3
(Kernel 2.4.18).

I've been using pppd (ppp-2.4.1-3 rpm) (in an ISDN-setup together with
capiplugin) for several month in persist-mode without problems with RH 7.2 and
kernel 2.4.9.
However, after the kernel upgrade, pppd dies when trying to reconnect after the
line was hung up. The problem seems to be some new kernel-code that causes the
PPPIOCDETACH ioctl to fail:

Jul  7 10:44:29 homer kernel: PPPIOCDETACH file->f_count=3

This corresponds to the following code in ppp_generic.c, which is patched in
Redhat's version of the kernel (patch: linux-2.4.17-selected-ac-bits.patch):

---------- snipp! ----------
        if (cmd == PPPIOCDETACH) {
                /*
                 * We have to be careful here... if the file descriptor
                 * has been dup'd, we could have another process in the
                 * middle of a poll using the same file *, so we had
                 * better not free the interface data structures -
                 * instead we fail the ioctl.  Even in this case, we
                 * shut down the interface if we are the owner of it.
                 * Actually, we should get rid of PPPIOCDETACH, userland
                 * (i.e. pppd) could achieve the same effect by closing
                 * this fd and reopening /dev/ppp.
                 */
                err = -EINVAL;
                if (pf->kind == INTERFACE) {
                        ppp = PF_TO_PPP(pf);
                        if (file == ppp->owner)
                                ppp_shutdown_interface(ppp);
                }
                if (atomic_read(&file->f_count) <= 2) {
                        ppp_release(inode, file);
                        err = 0;
                } else
                        printk(KERN_DEBUG "PPPIOCDETACH file->f_count=%d\n",
                               atomic_read(&file->f_count));
                return err;
        }
---------- snipp! ----------

The documentation tells:
* PPPIOCDETACH detaches the instance from the channel.  This ioctl is
  deprecated since the same effect can be achieved by closing the
  instance.  In order to prevent possible races this ioctl will fail
  with an EINVAL error if more than one file descriptor refers to this
  instance (i.e. as a result of dup(), dup2() or fork()). 

# /usr/sbin/lsof /dev/ppp
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
pppd    24396 root    4u   CHR  108,0      1311344 /dev/ppp
pppd    24396 root   10u   CHR  108,0      1311344 /dev/ppp



Version-Release number of selected component (if applicable):
kernel-2.4.18

How Reproducible:


Steps to Reproduce:
1. Run pppd in persist mode.
2. Unplug the telephone line

Actual Results:
pppd fails with "Couldn't release PPP unit: Invalid argument"

Expected Results:


Additional Information:
corresponding syslog entries are attached