Bug#290916: caused by zombie gdmgreeters... why?

[Václav Šmilauer]

I attach `ps -A | grep gdm`. After this particular gdm freeze I was able
to recover XDMCP functionality -KILLing parent processes of the defunct
gdmgreeters (i.e. the ones immediately above in the ps output).

The infamous line "whack_old_slave: GOT ANOTHER SIGTERM (or it was 10
secs already), killing slave again" repeated in the log until all defunct
processes were gone; they apparently prevented normal gdm operation.

What can be the cause of gdmgreeters going zombie?

---

 5231 ?        Ss     0:01 /usr/bin/gdm
 1642 ?        S      0:00 /usr/bin/gdm
 2110 ?        S      0:00 /usr/bin/gdm
 2114 ?        Zs     0:00 [gdmgreeter] <defunct>
 2592 ?        S      0:00 /usr/bin/gdm
 2597 ?        Zs     0:00 [gdmgreeter] <defunct>
32110 ?        S      0:00 /usr/bin/gdm
32114 ?        Ss     0:00 /usr/bin/gdmgreeter
32691 ?        S      0:00 /usr/bin/gdm
 7286 ?        S      0:00 /usr/bin/gdm
 9408 ?        S      0:00 /usr/bin/gdm
15320 ?        S      0:00 /usr/bin/gdm
16117 ?        S      0:00 /usr/bin/gdm
18213 ?        S      0:00 /usr/bin/gdm
18218 ?        Zs     0:00 [gdmgreeter] <defunct>
18686 ?        S      0:00 /usr/bin/gdm
18860 ?        S      0:00 /usr/bin/gdm
20828 ?        S      0:00 /usr/bin/gdm
29648 ?        S      0:00 /usr/bin/gdmflexiserver --sm-disable -a -c QUERY_LOGOUT_ACTION
 5197 pts/11   S+     0:00 grep gdm