Re: [External] Re: [PATCH v3 3/6] mm: hugetlb: fix a race between freeing and dissolving the page

Muchun Song
2021-01-12T10:13:48Z

On Tue, Jan 12, 2021 at 6:02 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Sun 10-01-21 20:40:14, Muchun Song wrote:
> [...]
> > @@ -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?

>
> > /*
> > * 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