Re: [PATCH v1] mm: bad_page() checks bad_flags instead of page->flags for hwpoison page

Vlastimil Babka
2016-05-18T07:30:45Z

On 05/17/2016 09:42 AM, Naoya Horiguchi wrote:
> There's a race window between checking page->flags and unpoisoning, which
> taints kernel with "BUG: Bad page state". That's overkill. It's safer to
> use bad_flags to detect hwpoisoned page.
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> ---
> mm/page_alloc.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git tmp/mm/page_alloc.c tmp_patched/mm/page_alloc.c
> index 5b269bc..4e0fa37 100644
> --- tmp/mm/page_alloc.c
> +++ tmp_patched/mm/page_alloc.c
> @@ -522,8 +522,8 @@ static void bad_page(struct page *page, const char *reason,
> static unsigned long nr_shown;
> static unsigned long nr_unshown;
>
> - /* Don't complain about poisoned pages */
> - if (PageHWPoison(page)) {
> + /* Don't complain about hwpoisoned pages */
> + if (bad_flags == __PG_HWPOISON) {

This will wrongly return prematurely on !CONFIG_MEMORY_FAILURE where
__PG_HWPOISON == 0 and bad_page() called for other reasons than bad flags?

> page_mapcount_reset(page); /* remove PageBuddy */
> return;
> }
>