Messages in this thread | | | Date | Wed, 16 Nov 2022 19:53:57 +0100 | From | David Hildenbrand <> | Subject | Re: [PATCH mm-unstable v1 20/20] mm: rename FOLL_FORCE to FOLL_PTRACE |
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On 16.11.22 19:16, Linus Torvalds wrote: > On Wed, Nov 16, 2022 at 2:30 AM David Hildenbrand <david@redhat.com> wrote: >> >> Let's make it clearer that functionality provided by FOLL_FORCE is >> really only for ptrace access. > > I'm not super-happy about this one. > > I do understand the "let's rename the bit so that no new user shows up". > > And it's true that the main traditional use is ptrace. > > But from the patch itself it becomes obvious that no, it's not *just* > ptrace. At least not yet. > > It's used for get_arg_page(), which uses it to basically look up (and > install) pages in the newly created VM. > > Now, I'm not entirely sure why it even uses FOLL_FORCE, - I think it > might be historical, because the target should always be the new stack > vma. > > Following the history of it is a big of a mess, because there's a > number of renamings and re-organizations, but it seems to go back to > 2007 and commit b6a2fea39318 ("mm: variable length argument support"). >
Right.
> Before that commit, we kept our own array of "this is the set of pages > that I will install in the new VM". That commit basically just inserts > the pages directly into the VM instead, getting rid of the array size > limitation. > > So at a minimum, I think that FOLL_FORCE would need to be removed > before any renaming to FOLL_PTRACE, because that's not some kind of > small random case. > > It *might* be as simple as just removing it, but maybe there's some > reason for having it that I don't immediately see.
Right, I have the same feeling. It might just be a copy-and-paste legacy leftover.
> > There _are_ also small random cases too, like get_cmdline(). Maybe > that counts as ptrace, but the execve() case most definitely does not.
I agree. I'd suggest moving forward without this (last) patch for now and figuring out how to further cleanup FOLL_FORCE usage on top.
@Andrew, if you intend to put this into mm-unstable, please drop the last patch for now.
-- Thanks,
David / dhildenb
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