Re: [PATCH v2 4/5] mm: Fix page reference leak in soft_offline_page()
From: Oscar Salvador <osalvador@suse.de>
Date: 2021-01-12 09:55:01
Also in:
lkml, nvdimm, stable
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@linux-foundation.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: David Hildenbrand <redacted>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <redacted>
Signed-off-by: Dan Williams <redacted>LGTM, thanks for catching this: Reviewed-by: Oscar Salvador <osalvador@suse.de> A nit below.
quoted hunk ↗ jump to hunk
--- 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.
quoted hunk ↗ jump to hunk
+ /** * 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