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. -- Jens Axboe
