The gdm in today's Rawhide (gdm-2.15.3-1) causes prefdm to keep trying to launch it as often as possible after the first spawn. Maybe an exit code changed or something? Reverting to gdm-2.15.0-1 makes the bug go away. Bug originally reported at: https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=192461
*** This bug has been marked as a duplicate of 192461 ***