This bug is copied from 
http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6951766.

Turns out this bug is introduced by commit b4f893eb294883909759fc9fd825eade1a9f308c, which is late than multi-seat branch created. So I'd like to file a separate bug to track it.

This happens when user logout, c-k-d trys to activate the reserved Login window session, and send out the two signals in change_active_session().
        g_signal_emit (seat, signals [ACTIVE_SESSION_CHANGED_FULL], 0, old_session, session);
        }
        g_signal_emit (seat, signals [ACTIVE_SESSION_CHANGED], 0, ssid);

The old_session is the session that user just log out, which should be removed after logout. I guess there is race condition here, if the old_session get unrefed to 0 before the g_signal_emit call, then core dump happens.

So the patch is like following:

diff --git a/src/ck-seat.c b/src/ck-seat.c
index dd2a387..72db11e 100644
--- a/src/ck-seat.c
+++ b/src/ck-seat.c
@@ -907,7 +907,10 @@ change_active_session (CkSeat    *seat,
          * must be sent when the database dump is finished it is
          * important that the '-full' signalled is emitted first. */
 
-        g_signal_emit (seat, signals [ACTIVE_SESSION_CHANGED_FULL], 0, old_sess
+        if (CK_IS_SESSION (old_session)) {
+                g_signal_emit (seat, signals [ACTIVE_SESSION_CHANGED_FULL], 0, 
+        }
+
         g_signal_emit (seat, signals [ACTIVE_SESSION_CHANGED], 0, ssid);
 
         if (old_session != NULL) {