Messages in this thread | | | Date | Thu, 2 Oct 2014 14:40:43 +0200 | From | Andrea Arcangeli <> | Subject | Re: [PATCH 2/4] mm: gup: add get_user_pages_locked and get_user_pages_unlocked |
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On Wed, Oct 01, 2014 at 10:06:27AM -0700, Andres Lagar-Cavilla wrote: > On Wed, Oct 1, 2014 at 8:51 AM, Peter Feiner <pfeiner@google.com> wrote: > > On Wed, Oct 01, 2014 at 10:56:35AM +0200, Andrea Arcangeli wrote: > >> + /* VM_FAULT_RETRY cannot return errors */ > >> + if (!*locked) { > >> + BUG_ON(ret < 0); > >> + BUG_ON(nr_pages == 1 && ret); > > > > If I understand correctly, this second BUG_ON is asserting that when > > __get_user_pages is asked for a single page and it is successfully gets the > > page, then it shouldn't have dropped the mmap_sem. If that's the case, then > > you could generalize this assertion to > > > > BUG_ON(nr_pages == ret);
Agreed.
> > Even more strict: > BUG_ON(ret >= nr_pages);
Agreed too, plus this should be quicker than my weaker check.
Maybe some BUG_ON can be deleted later or converted to VM_BUG_ON, but initially I feel safer with the BUG_ON considering that is a slow path.
> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com>
Thanks!
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