+ mmhwpoison-double-check-page-count-in-__get_any_page.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: mm,hwpoison: double-check page count in __get_any_page()
has been added to the -mm tree.  Its filename is
     mmhwpoison-double-check-page-count-in-__get_any_page.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mmhwpoison-double-check-page-count-in-__get_any_page.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mmhwpoison-double-check-page-count-in-__get_any_page.patch

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------------------------------------------------------
From: Naoya Horiguchi <naoya.horiguchi@nec.com>
Subject: mm,hwpoison: double-check page count in __get_any_page()

Soft offlining could fail with EIO due to the race condition with hugepage
migration.  This issuse became visible due to the change by previous patch
that makes soft offline handler take page refcount by its own.  We have no
way to directly pin zero refcount page, and the page considered as a zero
refcount page could be allocated just after the first check.

This patch adds the second check to find the race and gives us chance to
handle it more reliably.

Link: http://lkml.kernel.org/r/20200806184923.7007-13-nao.horiguchi@gmail.com
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reported-by: Qian Cai <cai@lca.pw>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dmitry Yakunin <zeil@yandex-team.ru>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.com>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory-failure.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/mm/memory-failure.c~mmhwpoison-double-check-page-count-in-__get_any_page
+++ a/mm/memory-failure.c
@@ -1707,6 +1707,9 @@ static int __get_any_page(struct page *p
 		} else if (is_free_buddy_page(p)) {
 			pr_info("%s: %#lx free buddy page\n", __func__, pfn);
 			ret = 0;
+		} else if (page_count(p)) {
+			/* raced with allocation */
+			ret = -EBUSY;
 		} else {
 			pr_info("%s: %#lx: unknown zero refcount page type %lx\n",
 				__func__, pfn, p->flags);
@@ -1723,6 +1726,9 @@ static int get_any_page(struct page *pag
 {
 	int ret = __get_any_page(page, pfn, flags);
 
+	if (ret == -EBUSY)
+		ret = __get_any_page(page, pfn, flags);
+
 	if (ret == 1 && !PageHuge(page) &&
 	    !PageLRU(page) && !__PageMovable(page)) {
 		/*
_

Patches currently in -mm which might be from naoya.horiguchi@nec.com are

mmhwpoison-cleanup-unused-pagehuge-check.patch
mm-hwpoison-remove-recalculating-hpage.patch
mmhwpoison-inject-dont-pin-for-hwpoison_filter.patch
mmhwpoison-introduce-mf_msg_unsplit_thp.patch
mmhwpoison-double-check-page-count-in-__get_any_page.patch