Re: [PATCH 3/6] block, fs: assert that key paths use iovecs, and nothing else

John Hubbard
2022-02-28T03:29:47Z

On 2/27/22 14:15, Al Viro wrote:
> On Sun, Feb 27, 2022 at 01:34:31AM -0800, jhubbard.send.patches@gmail.com wrote:
>> From: John Hubbard <jhubbard@nvidia.com>
>>
>> Upcoming changes to Direct IO will change it from acquiring pages via
>> get_user_pages_fast(), to calling pin_user_pages_fast() instead.
>>
>> Place a few assertions at key points, that the pages are IOVEC (user
>> pages), to enforce the assumptions that there are no kernel or pipe or
>> other odd variations being passed.
>
> Umm... And what should happen when O_DIRECT file gets passed to splice()?

OK, right, this is not going to work as-is.

Any of the remaining iov_iter_get_pages*() callers that do direct IO
(vmsplice, ceph, ...) will end up calling bio_release_pages(), which is
now unconditionally calling unpin_user_pages(). So this is just
completely broken.

And so, once again, I'm back to, "must convert the whole pile of
iov_iter_get_page*() callers at once".

Back to the drawing board.

thanks,
--
John Hubbard
NVIDIA