Re: [PATCH v2 2/3] futex: Create set_robust_list2

Peter Zijlstra
2024-11-05T12:10:18Z

On Mon, Nov 04, 2024 at 06:55:45PM -0300, André Almeida wrote:
> Hi Peter,
>
> Em 04/11/2024 08:22, Peter Zijlstra escreveu:
> > On Fri, Nov 01, 2024 at 01:21:46PM -0300, André Almeida wrote:
> > > @@ -1046,24 +1095,44 @@ static inline void exit_pi_state_list(struct task_struct *curr) { }
> > > static void futex_cleanup(struct task_struct *tsk)
> > > {
> > > + struct robust_list2_entry *curr, *n;
> > > + struct list_head *list2 = &tsk->robust_list2;
> > > +
> > > #ifdef CONFIG_64BIT
> > > if (unlikely(tsk->robust_list)) {
> > > - exit_robust_list64(tsk);
> > > + exit_robust_list64(tsk, tsk->robust_list);
> > > tsk->robust_list = NULL;
> > > }
> > > #else
> > > if (unlikely(tsk->robust_list)) {
> > > - exit_robust_list32(tsk);
> > > + exit_robust_list32(tsk, (struct robust_list_head32 *) tsk->robust_list);
> > > tsk->robust_list = NULL;
> > > }
> > > #endif
> > > #ifdef CONFIG_COMPAT
> > > if (unlikely(tsk->compat_robust_list)) {
> > > - exit_robust_list32(tsk);
> > > + exit_robust_list32(tsk, tsk->compat_robust_list);
> > > tsk->compat_robust_list = NULL;
> > > }
> > > #endif
> > > + /*
> > > + * Walk through the linked list, parsing robust lists and freeing the
> > > + * allocated lists
> > > + */
> > > + if (unlikely(!list_empty(list2))) {
> > > + list_for_each_entry_safe(curr, n, list2, list) {
> > > + if (curr->head != NULL) {
> > > + if (curr->list_type == ROBUST_LIST_64BIT)
> > > + exit_robust_list64(tsk, curr->head);
> > > + else if (curr->list_type == ROBUST_LIST_32BIT)
> > > + exit_robust_list32(tsk, curr->head);
> > > + curr->head = NULL;
> > > + }
> > > + list_del_init(&curr->list);
> > > + kfree(curr);
> > > + }
> > > + }
> > > if (unlikely(!list_empty(&tsk->pi_state_list)))
> > > exit_pi_state_list(tsk);
> >
> > I'm still digesting this, but the above seems particularly silly.
> >
> > Should not the legacy lists also be on the list of lists? I mean, it
> > makes no sense to have two completely separate means of tracking lists.
> >
>
> You are asking if, whenever someone calls set_robust_list() or
> compat_set_robust_list() to be inserted into &current->robust_list2 instead
> of using tsk->robust_list and tsk->compat_robust_list?

Yes, that.