On Tue, Jan 12, 2021 at 6:02 PM Michal Hocko [off-list ref] wrote:

On Sun 10-01-21 20:40:14, Muchun Song wrote:
[...]

quoted

@@ -1770,6 +1788,14 @@ int dissolve_free_huge_page(struct page *page)
              int nid = page_to_nid(head);
              if (h->free_huge_pages - h->resv_huge_pages == 0)
                      goto out;
+
+             /*
+              * We should make sure that the page is already on the free list
+              * when it is dissolved.
+              */
+             if (unlikely(!PageHugeFreed(head)))
+                     goto out;
+

Do you really want to report EBUSY in this case? This doesn't make much
sense to me TBH. I believe you want to return 0 same as when you race
and the page is no longer PageHuge.

Return 0 is wrong. Because the page is not freed to the buddy allocator.
IIUC, dissolve_free_huge_page returns 0 when the page is already freed
to the buddy allocator. Right?

quoted

              /*
               * Move PageHWPoison flag from head page to the raw error page,
               * which makes any subpages rather than the error page reusable.
--
2.11.0

--
Michal Hocko
SUSE Labs