linux-kernel - Re: [PATCH] mm/swap: Fix release_pages() when releasing devmap pages

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Date:   Thu, 23 May 2019 20:58:12 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Weiny, Ira" <ira.weiny@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>
Subject: Re: [PATCH] mm/swap: Fix release_pages() when releasing devmap pages

On Thu, May 23, 2019 at 3:37 PM <ira.weiny@...el.com> wrote:
>
> From: Ira Weiny <ira.weiny@...el.com>
>
> Device pages can be more than type MEMORY_DEVICE_PUBLIC.
>
> Handle all device pages within release_pages()
>
> This was found via code inspection while determining if release_pages()
> and the new put_user_pages() could be interchangeable.
>
> Cc: Jérôme Glisse <jglisse@...hat.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
>  mm/swap.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/swap.c b/mm/swap.c
> index 3a75722e68a9..d1e8122568d0 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -739,15 +739,14 @@ void release_pages(struct page **pages, int nr)
>                 if (is_huge_zero_page(page))
>                         continue;
>
> -               /* Device public page can not be huge page */
> -               if (is_device_public_page(page)) {
> +               if (is_zone_device_page(page)) {
>                         if (locked_pgdat) {
>                                 spin_unlock_irqrestore(&locked_pgdat->lru_lock,
>                                                        flags);
>                                 locked_pgdat = NULL;
>                         }
> -                       put_devmap_managed_page(page);
> -                       continue;
> +                       if (put_devmap_managed_page(page))

This "shouldn't" fail, and if it does the code that follows might get
confused by a ZONE_DEVICE page. If anything I would make this a
WARN_ON_ONCE(!put_devmap_managed_page(page)), but always continue
unconditionally.

Other than that you can add:

    Reviewed-by: Dan Williams <dan.j.williams@...el.com>