On 8/27/22 17:39, Al Viro wrote: > On Sun, Aug 28, 2022 at 01:38:57AM +0100, Al Viro wrote: >> On Sat, Aug 27, 2022 at 04:55:18PM -0700, John Hubbard wrote: >>> On 8/27/22 15:48, Al Viro wrote: >>>> On Sat, Aug 27, 2022 at 01:36:06AM -0700, John Hubbard wrote: >>>>> Convert the NFS Direct IO layer to use pin_user_pages_fast() and >>>>> unpin_user_page(), instead of get_user_pages_fast() and put_page(). >>>> >>>> Again, this stuff can be hit with ITER_BVEC iterators >>>> >>>>> - result = iov_iter_get_pages_alloc2(iter, &pagevec, >>>>> + result = dio_w_iov_iter_pin_pages_alloc(iter, &pagevec, >>>>> rsize, &pgbase); >>>> >>>> and this will break on those. >>> >>> If anyone has an example handy, of a user space program that leads >>> to this situation (O_DIRECT with ITER_BVEC), it would really help >>> me reach enlightenment a lot quicker in this area. :) >> >> Er... splice(2) to O_DIRECT-opened file on e.g. ext4? Or >> sendfile(2) to the same, for that matter... > > s/ext4/nfs/ to hit this particular codepath, obviously. aha, thanks. I do remember that you alerted me earlier to splice(2) problems, and I thought I'd neatly sidestepped those this time, by staying with user_backed_iter(i) cases. But I see that it's going to take something more, after all. thanks, -- John Hubbard NVIDIA
