manager: fix initial-setup -> user session transition

After the user goes through initial setup, the initial setup
program logs the user in.  Nowadays, this user session starts
on a new X server. The problem is, we also need the initial setup
X server to go away, and we need the login screen wayland server
to come up, all around the same time.

You can't quit one X server on a seat while starting another one up,
it doesn't like that, so there's caos, X server segfaults, and
unpredictable behavior as to "which session wins".

This commit fixes the problem by waiting until the greeter login screen
X server is started before starting the user session. This way they
don't stomp on each other's toes, and the user session ends up in
the foreground.

https://bugzilla.gnome.org/show_bug.cgi?id=745139

1 files changed, 72 insertions, 2 deletions

diff --git a/daemon/gdm-manager.c b/daemon/gdm-manager.c
index 34028663..77546b67 100644
--- a/daemon/gdm-manager.c
+++ b/daemon/gdm-manager.c
@@ -94,6 +94,8 @@ struct GdmManagerPrivate
         GDBusConnection          *connection;
         GDBusObjectManagerServer *object_manager;
 
+        StartUserSessionOperation *initial_login_operation;
+
 #ifdef  WITH_PLYMOUTH
         guint                     plymouth_is_running : 1;
 #endif
@@ -1454,6 +1456,42 @@ display_should_autologin (GdmManager *manager,
 }
 
 static void
+maybe_start_pending_initial_login (GdmManager *manager,
+                                   GdmDisplay *greeter_display)
+{
+        StartUserSessionOperation *operation;
+        char *greeter_seat_id = NULL;
+        char *user_session_seat_id = NULL;
+
+        /* There may be a user session waiting to be started.
+         * This would happen if we couldn't start it earlier because
+         * the login screen X server was coming up and two X servers
+         * can't be started on the same seat at the same time.
+         */
+
+        if (manager->priv->initial_login_operation == NULL) {
+                return;
+        }
+
+        operation = manager->priv->initial_login_operation;
+
+        g_object_get (G_OBJECT (greeter_display),
+                      "seat-id", &greeter_seat_id,
+                      NULL);
+        g_object_get (G_OBJECT (operation->session),
+                      "display-seat-id", &user_session_seat_id,
+                      NULL);
+
+        if (g_strcmp0 (greeter_seat_id, user_session_seat_id) == 0) {
+                start_user_session (manager, operation);
+                manager->priv->initial_login_operation = NULL;
+        }
+
+        g_free (greeter_seat_id);
+        g_free (user_session_seat_id);
+}
+
+static void
 set_up_greeter_session (GdmManager *manager,
                         GdmDisplay *display)
 {
@@ -1528,6 +1566,10 @@ on_display_status_changed (GdmDisplay *display,
                                         set_up_greeter_session (manager, display);
                                 }
                         }
+
+                        if (status == GDM_DISPLAY_MANAGED) {
+                                maybe_start_pending_initial_login (manager, display);
+                        }
                         break;
                 case GDM_DISPLAY_FAILED:
                 case GDM_DISPLAY_UNMANAGED:
@@ -1538,6 +1580,9 @@ on_display_status_changed (GdmDisplay *display,
                                 manager->priv->plymouth_is_running = FALSE;
                         }
 #endif
+
+
+                        maybe_start_pending_initial_login (manager, display);
                         break;
                 default:
                         break;
@@ -1608,6 +1653,7 @@ start_user_session (GdmManager *manager,
 
         gdm_session_start_session (operation->session,
                                    operation->service_name);
+
         destroy_start_user_session_operation (operation);
 }
 
@@ -1632,8 +1678,11 @@ create_display_for_user_session (GdmManager *self,
 static gboolean
 on_start_user_session (StartUserSessionOperation *operation)
 {
+        GdmManager *self = operation->manager;
         gboolean migrated;
         gboolean fail_if_already_switched = TRUE;
+        gboolean doing_initial_setup = FALSE;
+        gboolean starting_user_session_right_away = TRUE;
         GdmDisplay *display;
 
         g_debug ("GdmManager: start or jump to session");
@@ -1657,6 +1706,8 @@ on_start_user_session (StartUserSessionOperation *operation)
 
         display = get_display_for_user_session (operation->session);
 
+        g_object_get (G_OBJECT (display), "doing-initial-setup", &doing_initial_setup, NULL);
+
         if (gdm_session_get_display_mode (operation->session) == GDM_SESSION_DISPLAY_MODE_REUSE_VT) {
                 /* In this case, the greeter's display is morphing into
                  * the user session display. Kill the greeter on this session
@@ -1667,7 +1718,23 @@ on_start_user_session (StartUserSessionOperation *operation)
                 const char *session_id;
                 uid_t allowed_uid;
 
-                g_debug ("GdmManager: session has its display server, reusing our server for another login screen");
+                g_object_ref (display);
+                if (doing_initial_setup) {
+                        g_debug ("GdmManager: closing down initial setup display");
+                        gdm_display_stop_greeter_session (display);
+                        gdm_display_unmanage (display);
+                        gdm_display_finish (display);
+
+                        /* We can't start the user session until the finished display
+                         * starts to respawn (since starting an X server and bringing
+                         * one down at the same time is a no go)
+                         */
+                        g_assert (self->priv->initial_login_operation == NULL);
+                        self->priv->initial_login_operation = operation;
+                        starting_user_session_right_away = FALSE;
+                } else {
+                        g_debug ("GdmManager: session has its display server, reusing our server for another login screen");
+                }
 
                 /* The user session is going to follow the session worker
                  * into the new display. Untie it from this display and
@@ -1676,6 +1743,7 @@ on_start_user_session (StartUserSessionOperation *operation)
                 g_object_set_data (G_OBJECT (display), "gdm-embryonic-user-session", NULL);
                 g_object_set_data (G_OBJECT (operation->session), "gdm-display", NULL);
                 create_embryonic_user_session_for_display (operation->manager, display, allowed_uid);
+                g_object_unref (display);
 
                 /* Give the user session a new display object for bookkeeping purposes */
                 session_id = gdm_session_get_conversation_session_id (operation->session,
@@ -1685,7 +1753,9 @@ on_start_user_session (StartUserSessionOperation *operation)
                                                  session_id);
         }
 
-        start_user_session (operation->manager, operation);
+        if (starting_user_session_right_away) {
+                start_user_session (operation->manager, operation);
+        }
 
  out:
         return G_SOURCE_REMOVE;