Re: [PATCH RFC 1/1] futex: Create set_robust_list2

[André Almeida]

Em 24/10/2024 15:03, André Almeida escreveu:
> Hi Arnd,
>
> Em 24/10/2024 12:57, Arnd Bergmann escreveu:
> > On Thu, Oct 24, 2024, at 14:57, André Almeida wrote:
> > > This new syscall allows to set multiple list to the same process. There
> > > are two list types: 32 and 64 bit 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_list(tsk, curr->head);
> > > +                else if (curr->list_type == ROBUST_LIST_32BIT)
> > > +                    compat_exit_robust_list(tsk, curr->head);
> > > +                curr->head = NULL;
> > > +            }
> >
> > This looks like the behavior of a 32-bit task using
> > ROBUST_LIST_64BIT is different on native 32-bit kernels
> > compared to running on compat mode.
> >
> > Assuming we want them to behave the same way, did you intend
> > ROBUST_LIST_64BIT to refer to 64-bit pointers on 32-bit
> > tasks, or should they use normal word-size pointers?
>
> Oh right, I haven't covered that indeed. I think I would need to have 
> something like:
>
> static void exit_robust_list_64()
> static void exit_robust_list_32()
>
> And then each function would use explicit sizes for pointers. Also, I 
> would rewrite the conditions to make that every combination of 64/32bit 
> kernel/app calls the appropriated function.

Something like this:

#ifdef CONFIG_64BIT
	if (unlikely(tsk->robust_list)) {
		exit_robust_list_64bit(tsk, tsk->robust_list);
		tsk->robust_list = NULL;
	}
#else
	if (unlikely(tsk->robust_list)) {
		exit_robust_list_32bit(tsk, tsk->robust_list);
		tsk->robust_list = NULL;
	}
#endif

#ifdef CONFIG_COMPAT
	if (unlikely(tsk->compat_robust_list)) {
		exit_robust_32bit(tsk, tsk->compat_robust_list);
		tsk->compat_robust_list = NULL;
	}
#endif

	/* Simplified */
	list_for_each_entry_safe(curr, n, list2, list) {
		if (curr->list_type == ROBUST_LIST_64BIT)
			exit_robust_list_64bit(tsk, curr->head);
		else if (curr->list_type == ROBUST_LIST_32BIT)
			exit_robust_list_32bit(tsk, curr->head);
	}