Re: [PATCH] mm/gup: Let __get_user_pages_locked() return -EINTR for fatal signal

[Linus Torvalds]

On Wed, Apr 8, 2020 at 8:59 AM Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> __get_user_pages_locked() will return 0 instead of -EINTR after commit
> 4426e945df588 which added extra code to allow gup detect fatal signal
> faster.  Restore that behavior.

I've applied this, but it's worth noting that
__get_user_pages_locked() can still return 0 in other situations.

I realize that "I got zero pages" is a valid return value, but I do
wonder if we should make the rule be that a zero return value isn't
possible (return -EAGAIN or whatever if you doin't have the
EFAULT/EINTR conditions).

So that you'd always get either an error, or a successful number of pages.

The only case where __get_user_pages_locked() might return zero is if
you pass in a zero 'nr_pages', although I suspect even for that case
returning -EINVAL might be a better option.

Anyway, this is not a new issue, but I thought I'd mention it.

             Linus