Re: [PATCH v3 3/4] mm: BUG_ON to avoid NULL deference while __GFP_NOFAIL fails

[Barry Song <21cnbao@gmail.com>]

On Tue, Aug 20, 2024 at 12:51 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 19.08.24 14:49, Christoph Hellwig wrote:
> > On Mon, Aug 19, 2024 at 02:33:06PM +0200, David Hildenbrand wrote:
> >> It should all be caught during testing either way. And if some OOT module
> >> does something nasty, that's not our responsibility.
> >>
> >> BUG_ON is not a way to write assertions into the code.
> >
> > So you'd rather create exploits than crashing on a fundamental API
> > violation?  That's exactly what the series is trying to fix.
>
> I'd rather have a sane API that doesn't even allow this level of
> flexibility with NOFAIL.

yes, i have already sent a RFC enforcing direct_reclamation:
https://www.spinics.net/lists/linux-mm/msg394659.html

somehow, it is not ready yet. i think Christoph prefers scope
api rather than GFP_NOFAIL which definitely has
__GFP_DIRECT_RECLAIM set. I guess you know I have
at least  5 series running, so it will happen soon though.

>
> But probably I'm missing more details here why this all has to be so
> complicated ;)

enforcing direct_reclamation is right and will work for a reasonable size.
but for this overflow size, even if we enforce direct_reclamation
in GFP_NOFAIL, we are still failing.

>
> --
> Cheers,
>
> David / dhildenb
>