linux-kernel - Re: [PATCH v1] mm, hwpoison: add is_free_buddy

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Date:   Wed, 8 Sep 2021 20:22:14 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>
Cc:     Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tony Luck <tony.luck@...el.com>,
        Oscar Salvador <osalvador@...e.de>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] mm, hwpoison: add is_free_buddy_page() in HWPoisonHandlable()

On Wed, Sep 8, 2021 at 5:41 PM Naoya Horiguchi
<naoya.horiguchi@...ux.dev> wrote:
>
> From: Naoya Horiguchi <naoya.horiguchi@....com>
>
> commit fcc00621d88b ("mm/hwpoison: retry with shake_page() for
> unhandlable pages") changes the return value of __get_hwpoison_page() to
> retry for transiently unhandlable cases.  However, __get_hwpoison_page()
> currently fails to properly judge buddy pages as handlable, so hard/soft
> offline for buddy pages always fail as "unhandlable page".  This is
> totally regrettable.
>
> So let's add is_free_buddy_page() in HWPoisonHandlable(), so that
> __get_hwpoison_page() returns different return values between buddy
> pages and unhandlable pages as intended.
>
> Fixes: fcc00621d88b ("mm/hwpoison: retry with shake_page() for unhandlable pages")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> ---
>  mm/memory-failure.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git v5.14-rc7-mmotm-2021-08-23-16-42/mm/memory-failure.c v5.14-rc7-mmotm-2021-08-23-16-42_patched/mm/memory-failure.c
> index 60df8fcd0444..3416c55be810 100644
> --- v5.14-rc7-mmotm-2021-08-23-16-42/mm/memory-failure.c
> +++ v5.14-rc7-mmotm-2021-08-23-16-42_patched/mm/memory-failure.c
> @@ -1126,7 +1126,7 @@ static int page_action(struct page_state *ps, struct page *p,
>   */
>  static inline bool HWPoisonHandlable(struct page *page)
>  {
> -       return PageLRU(page) || __PageMovable(page);
> +       return PageLRU(page) || __PageMovable(page) || is_free_buddy_page(page);

It seems to work. Although this may change the return value of
get_any_page() to 1 when MF_COUNT_INCREASED is set. This may cause
soft offline to mishandle free buddy page, but MF_COUNT_INCREASED is
only set when madvise is used, and madvise definitely can't soft
offline free buddy page. It did take me a while to figure out this
trick. Maybe need some refactor?

Anyway this patch looks fine to me. Reviewed-by: Yang Shi <shy828301@...il.com>

>  }
>
>  static int __get_hwpoison_page(struct page *page)
> --
> 2.25.1
>