Re: [PATCH v4 4/5] mm: Fix page reference leak in soft_offline_page()
From: HORIGUCHI NAOYA (堀口 直也) <hidden>
Date: 2021-01-14 01:53:04
Also in:
linux-mm, lkml, nvdimm
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@linux-foundation.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Reviewed-by: David Hildenbrand <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: <redacted>
Signed-off-by: Dan Williams <redacted>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
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); +} + /** * 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; }