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Date: Tue, 12 Jan 2021 10:53:50 +0100 From: Oscar Salvador <osalvador@...e.de> To: Dan Williams <dan.j.williams@...el.com> Cc: 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@...r.kernel.org, vishal.l.verma@...el.com, linux-nvdimm@...ts.01.org, 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 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@...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. > + > /** > * 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
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