On Tue, Jul 04, 2023 at 06:22:06AM -0700, Linus Torvalds wrote:
> On Tue, 4 Jul 2023 at 00:36, <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Subject: gup: avoid stack expansion warning for known-good case
> >
> > From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> >
> > commit eee9c708cc89b4600c6e6cdda5bc2b8b4dad96cb upstream.
>
> This patch shouldn't be needed in stable.
>
> If you look a few lines up, you'll see that the exact same logic of
> vma_lookup -> expand_stack is already there.
>
> The only reason it's there in mainline is that the interaction with
> commit ca5e863233e8 ("mm/gup: remove vmas parameter from
> get_user_pages_remote()") caused the vma lookup (and thus expand) to
> be done *after* doing the GUP.
>
> So in mainline, this
>
> > + /* Avoid triggering the temporary warning in __get_user_pages */
> > + if (!vma_lookup(mm, addr) && !expand_stack(mm, addr))
> > + return 0;
>
> ends up being a "let's do an extra vma_lookup() -> expand_stack()
> sequence early" because the "real one" is done later.
>
> But in the original patches (and the backports), it was always done
> early, so this patch just duplicates what's already there.
Ah, I missed that this was a "duplicate" check here, thanks for letting
me know, I'll go drop this from all of the queues.
greg k-h
