Re: [PATCH v4 4/6] io_uring: rsrc: avoid use of vmas parameter in pin_user_pages()

[Pavel Begunkov]

On 4/19/23 21:15, Jens Axboe wrote:
> On 4/19/23 12:24?PM, Jason Gunthorpe wrote:
> > On Wed, Apr 19, 2023 at 07:23:00PM +0100, Matthew Wilcox wrote:
> > > On Wed, Apr 19, 2023 at 07:18:26PM +0100, Lorenzo Stoakes wrote:
> > > > So even if I did the FOLL_ALLOW_BROKEN_FILE_MAPPING patch series first, I
> > > > would still need to come along and delete a bunch of your code
> > > > afterwards. And unfortunately Pavel's recent change which insists on not
> > > > having different vm_file's across VMAs for the buffer would have to be
> > > > reverted so I expect it might not be entirely without discussion.
> > >
> > > I don't even understand why Pavel wanted to make this change.  The
> > > commit log really doesn't say.
> > >
> > > commit edd478269640
> > > Author: Pavel Begunkov <asml.silence@xxxxxxxxx>
> > > Date:   Wed Feb 22 14:36:48 2023 +0000
> > >
> > >      io_uring/rsrc: disallow multi-source reg buffers
> > >
> > >      If two or more mappings go back to back to each other they can be passed
> > >      into io_uring to be registered as a single registered buffer. That would
> > >      even work if mappings came from different sources, e.g. it's possible to
> > >      mix in this way anon pages and pages from shmem or hugetlb. That is not
> > >      a problem but it'd rather be less prone if we forbid such mixing.
> > >
> > >      Cc: <stable@xxxxxxxxxxxxxxx>
> > >      Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
> > >      Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> > >
> > > It even says "That is not a problem"!  So why was this patch merged
> > > if it's not fixing a problem?
> > >
> > > It's now standing in the way of an actual cleanup.  So why don't we
> > > revert it?  There must be more to it than this ...
> >
> > https://lore.kernel.org/all/61ded378-51a8-1dcb-b631-fda1903248a9@xxxxxxxxx/
>
> Let's just kill that patch that, I can add a revert for 6.4. I had
> forgotten about that patch and guess I didn't realize that most of the
> issue do in fact just stem from that.

Well, we're now trading uapi sanity for cleanups, I don't know
what I should take out of it.

--
Pavel Begunkov