On Tue, Mar 12, 2024 at 06:23:43PM -0700, Jane Chu wrote:
> I noticed this recently
OK, this is entirely different, so I'm going to start a new thread ;-)
> * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
> * they are not mapped.
> *
> * Returns 0 if the hugepage is split successfully.
> * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
> * us.
> */
> int split_huge_page_to_list(struct page *page, struct list_head *list)
> {
>
> I have a test case with poisoned shmem THP page that was mlocked and
>
> GUP pinned (FOLL_LONGTERM|FOLL_WRITE), but the split succeeded.
I'm going to blame John for this! There's no reference to pincount
anywhere in huge_memory.c, so I have no clue how this comment is even
close to true, nor do I understand how it could be done, since we don't
know which pages in a folio are pinned.
I think we have to prohibit splits of folios that are GUP pinned.
