Re: [PATCH] mm: check VMA flags to avoid invalid PROT_NONE NUMA balancing

Hugh Dickins
2016-10-07T18:16:52Z

On Fri, 7 Oct 2016, Lorenzo Stoakes wrote:
> On Fri, Oct 07, 2016 at 08:34:15AM -0700, Linus Torvalds wrote:
> > Would you be willing to look at doing that kind of purely syntactic,
> > non-semantic cleanup first?
>
> Sure, more than happy to do that! I'll work on a patch for this.
>
> > I think that if we end up having the FOLL_FORCE semantics, we're
> > actually better off having an explicit FOLL_FORCE flag, and *not* do
> > some kind of implicit "under these magical circumstances we'll force
> > it anyway". The implicit thing is what we used to do long long ago, we
> > definitely don't want to.
>
> That's a good point, it would definitely be considerably more 'magical', and
> expanding the conditions to include uprobes etc. would only add to that.
>
> I wondered about an alternative parameter/flag but it felt like it was
> more-or-less FOLL_FORCE in a different form, at which point it may as well
> remain FOLL_FORCE :)

Adding Jan Kara (and Dave Hansen) to the Cc list: I think they were
pursuing get_user_pages() cleanups last year (which would remove the
force option from most callers anyway), and I've lost track of where
that all got to. Lorenzo, please don't expend a lot of effort before
checking with Jan.

Hugh