Re: [PATCH v2 4/5] mm: Fix page reference leak in soft_offline_page()
On Tue, Jan 12, 2021 at 1:54 AM Oscar Salvador wrote:
>
> 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_*.
Sure.
>
> > 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
> > Cc: Naoya Horiguchi
> > Cc: David Hildenbrand
> > Cc: Michal Hocko
> > Cc: Oscar Salvador
> > Cc:
> > Signed-off-by: Dan Williams
>
> LGTM, thanks for catching this:
>
> Reviewed-by: Oscar Salvador
>
> 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.
I'll take another look, it felt cluttered...
>
> > +
> > /**
> > * 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.
>
I did not, more future proofing / documenting against refactoring that
fails to consider that case.
Re: [PATCH v2 4/5] mm: Fix page reference leak in soft_offline_page()
On 12.01.21 10:34, 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.
>
> 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
> Cc: Naoya Horiguchi
> Cc: David Hildenbrand
> Cc: Michal Hocko
> Cc: Oscar Salvador
> Cc:
> Signed-off-by: Dan Williams
> ---
> 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;
> }
Reviewed-by: David Hildenbrand
--
Thanks,
David / dhildenb
Re: [PATCH v2 4/5] mm: Fix page reference leak in soft_offline_page()
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
> Cc: Naoya Horiguchi
> Cc: David Hildenbrand
> Cc: Michal Hocko
> Cc: Oscar Salvador
> Cc:
> Signed-off-by: Dan Williams
LGTM, thanks for catching this:
Reviewed-by: Oscar Salvador
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
