On Tue, Jan 12, 2021 at 01:34:58AM -0800, Dan Williams wrote:
> The conversion to move pfn_to_online_page() internal to
> soft_offline_page() missed that the get_user_pages() reference needs to
> be dropped when pfn_to_online_page() fails.
I would be more specific here wrt. get_user_pages (madvise).
soft_offline_page gets called from more places besides madvise_*.
> When soft_offline_page() is handed a pfn_valid() &&
> !pfn_to_online_page() pfn the kernel hangs at dax-device shutdown due to
> a leaked reference.
>
> Fixes: feec24a6139d ("mm, soft-offline: convert parameter to pfn")
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Naoya Horiguchi <nao.horiguchi@xxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
LGTM, thanks for catching this:
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
A nit below.
> ---
> mm/memory-failure.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 5a38e9eade94..78b173c7190c 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1885,6 +1885,12 @@ static int soft_offline_free_page(struct page *page)
> return rc;
> }
>
> +static void put_ref_page(struct page *page)
> +{
> + if (page)
> + put_page(page);
> +}
I am not sure this warrants a function.
I would probably go with "if (ref_page).." in the two corresponding places,
but not feeling strong here.
> +
> /**
> * soft_offline_page - Soft offline a page.
> * @pfn: pfn to soft-offline
> @@ -1910,20 +1916,26 @@ static int soft_offline_free_page(struct page *page)
> int soft_offline_page(unsigned long pfn, int flags)
> {
> int ret;
> - struct page *page;
> bool try_again = true;
> + struct page *page, *ref_page = NULL;
> +
> + WARN_ON_ONCE(!pfn_valid(pfn) && (flags & MF_COUNT_INCREASED));
Did you see any scenario where this could happen? I understand that you are
adding this because we will leak a reference in case pfn is not valid anymore.
--
Oscar Salvador
SUSE L3
