On Fri, Jul 7, 2023 at 7:57 PM Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
>
> On 2023/7/8 4:19, Jiaqi Yan wrote:
> > Add the functionality, is_raw_hwp_subpage, to tell if a subpage of a
> > hugetlb folio is a raw HWPOISON page. This functionality relies on
> > RawHwpUnreliable to be not set; otherwise hugepage's raw HWPOISON list
> > becomes meaningless.
> >
> > is_raw_hwp_subpage needs to hold hugetlb_lock in order to synchronize
> > with __get_huge_page_for_hwpoison, who iterates and inserts an entry to
> > raw_hwp_list. llist itself doesn't ensure insertion is synchornized with
> > the iterating used by __is_raw_hwp_list. Caller can minimize the
> > overhead of lock cycles by first checking if folio / head page's
> > HWPOISON flag is set.
> >
> > Exports this functionality to be immediately used in the read operation
> > for hugetlbfs.
> >
> > Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > Reviewed-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> > Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
> > ---
> > include/linux/hugetlb.h | 19 +++++++++++++++++++
> > include/linux/mm.h | 7 +++++++
> > mm/hugetlb.c | 10 ++++++++++
> > mm/memory-failure.c | 34 ++++++++++++++++++++++++----------
> > 4 files changed, 60 insertions(+), 10 deletions(-)
> > ...
> > -static inline struct llist_head *raw_hwp_list_head(struct folio *folio)
> > +bool __is_raw_hwp_subpage(struct folio *folio, struct page *subpage)
> > {
> > - return (struct llist_head *)&folio->_hugetlb_hwpoison;
> > + struct llist_head *raw_hwp_head;
> > + struct raw_hwp_page *p, *tmp;
> > + bool ret = false;
> > +
> > + if (!folio_test_hwpoison(folio))
> > + return false;
> > +
> > + /*
> > + * When RawHwpUnreliable is set, kernel lost track of which subpages
> > + * are HWPOISON. So return as if ALL subpages are HWPOISONed.
> > + */
> > + if (folio_test_hugetlb_raw_hwp_unreliable(folio))
> > + return true;
> > +
> > + raw_hwp_head = raw_hwp_list_head(folio);
> > + llist_for_each_entry_safe(p, tmp, raw_hwp_head->first, node) {
>
> Since we don't free the raw_hwp_list, does llist_for_each_entry works same as llist_for_each_entry_safe?
>
> > + if (subpage == p->page) {
> > + ret = true;
> > + break;
> > + }
> > + }
> > +
> > + return ret;
> > }
>
> It seems there's a race between __is_raw_hwp_subpage and unpoison_memory:
> unpoison_memory __is_raw_hwp_subpage
> if (!folio_test_hwpoison(folio)) -- hwpoison is set
> folio_free_raw_hwp llist_for_each_entry_safe raw_hwp_list
> llist_del_all ..
> folio_test_clear_hwpoison
>
Thanks Miaohe for raising this concern.
> But __is_raw_hwp_subpage is used in hugetlbfs, unpoison_memory couldn't reach here because there's a
> folio_mapping == NULL check before folio_free_raw_hwp.
I agree. But in near future I do want to make __is_raw_hwp_subpage
work for shared-mapping hugetlb, so it would be nice to work with
unpoison_memory. It doesn't seem to me that holding mf_mutex in
__is_raw_hwp_subpage is nice or even absolutely correct. Let me think
if I can come up with something in v4.
>
> Anyway, this patch looks good to me.
>
> Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Thanks.
>
