libweston: clear parent_view when the parent view is destroyed

When a view is destroyed then the views of subsurfaces remain until the view list is rebuilt for the next repaint. During that time view->parent_view contains an invalid pointer and weston will crash when it tries to access the view.

This happens for a surface with subsurfaces with views on two different outputs with the ivi-shell:

When the surface is destroyed then the destroy handler of the ivi-shell (shell_handle_surface_destroy()) may be called first. It will (indirectly) destroy the view of the main surface with weston_view_destroy(). Next the surface destroy handler of the subsurfaces (subsurface_handle_parent_destroy() is called. It will unmap the first view of the subsurface. Here weston_surface_assign_output() is called which tries to find the output of the second view and accesses the now invalid view->parent_view in the process.

There are probably other ways to trigger similar crashes.

To avoid this, clear view->parent_view when the parent view is destroyed.

Signed-off-by: Michael Olbrich m.olbrich@pengutronix.de