GitLab

free_pi_state and exit_pi_state_list both clean up futex_pi_state's.
exit_pi_state_list takes the hb lock first, and most callers of
free_pi_state do too. requeue_pi doesn't, which means free_pi_state
can free the pi_state out from under exit_pi_state_list. For example:

task A                            |  task B
exit_pi_state_list                |
  pi_state =                      |
      curr->pi_state_list->next   |
                                  |  futex_requeue(requeue_pi=1)
                                  |    // pi_state is the same as
                                  |    // the one in task A
                                  |    free_pi_state(pi_state)
                                  |      list_del_init(&pi_state->list)
                                  |      kfree(pi_state)
  list_del_init(&pi_state->list)  |

Move the free_pi_state calls in requeue_pi to before it drops the hb
locks which it's already holding.

[ tglx: Re...