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Date: Tue, 12 Jan 2021 12:03:55 -0800 From: Dan Williams <dan.j.williams@...el.com> To: Oscar Salvador <osalvador@...e.de> Cc: Linux MM <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, Naoya Horiguchi <nao.horiguchi@...il.com>, David Hildenbrand <david@...hat.com>, Michal Hocko <mhocko@...nel.org>, stable <stable@...r.kernel.org>, Vishal L Verma <vishal.l.verma@...el.com>, linux-nvdimm <linux-nvdimm@...ts.01.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: 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 <osalvador@...e.de> 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 <akpm@...ux-foundation.org> > > Cc: Naoya Horiguchi <nao.horiguchi@...il.com> > > Cc: David Hildenbrand <david@...hat.com> > > Cc: Michal Hocko <mhocko@...nel.org> > > Cc: Oscar Salvador <osalvador@...e.de> > > Cc: <stable@...r.kernel.org> > > Signed-off-by: Dan Williams <dan.j.williams@...el.com> > > LGTM, thanks for catching this: > > Reviewed-by: Oscar Salvador <osalvador@...e.de> > > 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.
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