[Bug libgomp/81591] segmentation fault when using priorities of nested tasks

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81591

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
There's

static void inline
priority_queue_downgrade_task (enum priority_queue_type type,
                               struct priority_queue *head,
                               struct gomp_task *task)
{
#if _LIBGOMP_CHECKING_
  if (!priority_queue_task_in_queue_p (type, head, task))
    gomp_fatal ("Attempt to downgrade missing task %p", task);
#endif
  if (priority_queue_multi_p (head))
    {
      struct priority_list *list
        = priority_queue_lookup_priority (head, task->priority);
      priority_list_downgrade_task (type, list, task);

so maybe you can build libgomp with _LIBGOMP_CHECKING_ to help track this down?
(just change libgomp/libgomp.h)