Please note that the X server is NOT crashing. The X server does not exit and restart when the login fails. It's the same instance of the X server, the same /var/log/Xorg.0.log file, afterwards.

Here's what shows up in /var/log/messages when I attempt to log in:

May 21 07:34:21 jik2 TIFIER=systemd-logind[759]: New session 72 of user jik.
May 21 07:34:22 jik2 TIFIER=systemd-logind[759]: Removed session 72.
May 21 07:34:22 jik2 dbus-daemon[772]: dbus[772]: [system] Activating service name='net.reactivated.Fprint' (using servicehelper)
May 21 07:34:22 jik2 dbus[772]: [system] Activating service name='net.reactivated.Fprint' (using servicehelper)
May 21 07:34:22 jik2 dbus-daemon[772]: Launching FprintObject
May 21 07:34:22 jik2 dbus-daemon[772]: dbus[772]: [system] Successfully activated service 'net.reactivated.Fprint'
May 21 07:34:22 jik2 dbus[772]: [system] Successfully activated service 'net.reactivated.Fprint'
May 21 07:34:22 jik2 dbus-daemon[772]: ** Message: D-Bus service launched with name: net.reactivated.Fprint
May 21 07:34:22 jik2 dbus-daemon[772]: ** Message: entering main loop

Note the oddly truncated "TIFIER" tag at the beginning of some of the messages. I don't know if that's relevant. It wasn't happening until after last night's update.

Downgrading from systemd-44-9 to systemd-44-8 makes the problem go away. Changing component to systemd.

Note also that before downgrading, I tried doing "systemctl restart prefdm.service" to see if that, rather than a full reboot, would be sufficient, and it wasn't. I got flashing back and forth between VT's and the attached interesting sequence of events in /var/log/messages.

Note also that I have SELinux disabled.

Created attachment 585826 [details]
/var/log/messages when prefdm.service is restarted

Thanks for the report.
I can reproduce this.

After the user session is set is initialized and ready to be launched, gdm has code (something) like this to make sure there's no other sessions that should be jumped to instead:

session_to_use = NULL;
found_existing_inactive_session = FALSE;
sd_seat_get_sessions (slave->priv->display_seat_id, &sessions, ...)
for (each session in sessions) {
  sd_session_get_type (session, &type);
  sd_session_get_uid (session, &uid);
  is_active = sd_session_is_active (session) > 0;

  if (type is not "x11")
     continue;

  if (uid is not uid of user)
     continue;

  if (!found_existing_inactive_session) {
      /* session_to_use may have the just initialized, 
         active session in it from a previous iteration
         of this loop */
      session_to_use = session;
      
      if (!is_active)
          found_existing_inactive_session = TRUE; 
  }
}
return session_to_use;

if we're jumping to a text VT, then there's a good chance that text login sessions at the console are getting tagged with the type "x11" so they aren't getting skipped in the "if (type is not 'x11') continue" line above.

In systemd-44-9.fc17 I backported commit "logind: close FIFO before ending sessions cleanly" ( http://cgit.freedesktop.org/systemd/systemd/commit/?id=75c8e3cffd7da8eede614cf61384957af2c82a29 ). The bug goes away if this commit is reverted.

With systemd-44-9.fc17 after logging out of Gnome the user's session does not disappear immediately. It remains alive because of two remaining processes:

# loginctl session-status 3
3 - michich (1000)
	   Since: Mon, 21 May 2012 23:23:54 +0200; 22s ago
	  Leader: 799
	    Seat: seat0; vc1
	 Display: :0
	 Service: gdm-password; type x11; class user
	  Active: no
	  CGroup: name=systemd:/user/michich/3
		  ├ 1056 /usr/bin/pulseaudio --start
		  └ 1063 /usr/libexec/pulse/gconf-helper

You can see I had a Gnome session on vc1 and I logged out of it. The session did not go away entirely even though the leader process is gone.
GDM is now showing on vc2. If I try to login as "michich" again, GDM will just switch to vc1 (where nothing of interest is) because of the inactive session above.
If I wait a few more seconds, the two processes will exit and I can login normally.

(In reply to comment #6)
> In systemd-44-9.fc17 I backported commit "logind: close FIFO before ending
> sessions cleanly" (
> http://cgit.freedesktop.org/systemd/systemd/commit/
> ?id=75c8e3cffd7da8eede614cf61384957af2c82a29 ). The bug goes away if this
> commit is reverted.

I reverted the patch in systemd-44-11.fc17.
Moving this bug to Rawhide.

ah that's because of bug 814690 probably.

This is fixed in git and soon F18.

systemd-190-1.fc18 has been submitted as an update for Fedora 18.
https://admin.fedoraproject.org/updates/systemd-190-1.fc18

Package systemd-191-2.fc18, rtkit-0.11-3.fc18:
* should fix your issue,
* was pushed to the Fedora 18 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=updates-testing systemd-191-2.fc18 rtkit-0.11-3.fc18'
as soon as you are able to, then reboot.
Please go to the following url:
https://admin.fedoraproject.org/updates/FEDORA-2012-14581/rtkit-0.11-3.fc18,systemd-191-2.fc18
then log in and leave karma (feedback).

Package glibc-2.16-17.fc18, systemd-192-1.fc18, selinux-policy-3.11.1-23.fc18, rtkit-0.11-3.fc18:
* should fix your issue,
* was pushed to the Fedora 18 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=updates-testing glibc-2.16-17.fc18 systemd-192-1.fc18 selinux-policy-3.11.1-23.fc18 rtkit-0.11-3.fc18'
as soon as you are able to, then reboot.
Please go to the following url:
https://admin.fedoraproject.org/updates/FEDORA-2012-14581/selinux-policy-3.11.1-23.fc18,rtkit-0.11-3.fc18,systemd-192-1.fc18,glibc-2.16-17.fc18
then log in and leave karma (feedback).

Package glibc-2.16-17.fc18, rtkit-0.11-3.fc18, systemd-193-1.fc18:
* should fix your issue,
* was pushed to the Fedora 18 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=updates-testing glibc-2.16-17.fc18 rtkit-0.11-3.fc18 systemd-193-1.fc18'
as soon as you are able to, then reboot.
Please go to the following url:
https://admin.fedoraproject.org/updates/FEDORA-2012-14581/rtkit-0.11-3.fc18,systemd-193-1.fc18,glibc-2.16-17.fc18
then log in and leave karma (feedback).