On Wed, Jan 13, 2021 at 04:43:32PM -0800, Dan Williams wrote:
> The conversion to move pfn_to_online_page() internal to
> soft_offline_page() missed that the get_user_pages() reference taken by
> the madvise() path needs to be dropped when pfn_to_online_page() fails.
> Note the direct sysfs-path to soft_offline_page() does not perform a
> get_user_pages() lookup.
>
> 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: Michal Hocko <mhocko@xxxxxxxxxx>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
I'm OK if we don't have any other better approach, but the proposed changes
make code a little messy, and I feel that get_user_pages() might be the
right place to fix. Is get_user_pages() expected to return struct page with
holding refcount for offline valid pages? I thought that such pages are
only used by drivers for dax-devices, but that might be wrong. Can I ask for
a little more explanation from this perspective?
Thanks,
Naoya Horiguchi
> ---
> 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);
> +}
> +
> /**
> * 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));
>
> if (!pfn_valid(pfn))
> return -ENXIO;
> + if (flags & MF_COUNT_INCREASED)
> + ref_page = pfn_to_page(pfn);
> +
> /* Only online pages can be soft-offlined (esp., not ZONE_DEVICE). */
> page = pfn_to_online_page(pfn);
> - if (!page)
> + if (!page) {
> + put_ref_page(ref_page);
> return -EIO;
> + }
>
> if (PageHWPoison(page)) {
> pr_info("%s: %#lx page already poisoned\n", __func__, pfn);
> - if (flags & MF_COUNT_INCREASED)
> - put_page(page);
> + put_ref_page(ref_page);
> return 0;
> }
>
>
