On 8/27/22 17:39, Al Viro wrote:

On Sun, Aug 28, 2022 at 01:38:57AM +0100, Al Viro wrote:

quoted

On Sat, Aug 27, 2022 at 04:55:18PM -0700, John Hubbard wrote:

quoted

On 8/27/22 15:48, Al Viro wrote:

quoted

On Sat, Aug 27, 2022 at 01:36:06AM -0700, John Hubbard wrote:

quoted

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

quoted

-		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