It looks like, it's possible that cores for some threads
were allocated, but not for all - allocation failed in
pstree_alloc_cores(). And after that we will dereference
NULL pointer as pstree_free_cores() doesn't check pointer:

pstree.c:28:6: warning: Access to field 'tc' results in a dereference of a null pointer (loaded from variable 'core')
        if (core->tc && core->tc->timers)
            ^~~~~~~~
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>