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Date: Fri, 7 Oct 2016 11:16:26 -0700 (PDT)
From: Hugh Dickins <hughd@google.com>
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To: Lorenzo Stoakes <lstoakes@gmail.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Jan Kara <jack@suse.cz>, Dave Hansen <dave.hansen@linux.intel.com>,
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        robert@ocallahan.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: check VMA flags to avoid invalid PROT_NONE NUMA
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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