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
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.
Anyway, this patch looks good to me.
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Thanks.
