From 9eb1ae720aac3c1a3c6d519bd12858f103987f88 Mon Sep 17 00:00:00 2001
From: Naoya Horiguchi <naoya.horiguchi@nec.com>
Date: Mon, 22 Feb 2021 10:56:03 +0800
Subject: [PATCH] mm, hwpoison: double-check page count in __get_any_page()

mainline inclusion
from mainline-v5.10-rc1
commit 1f2481ddbe444de5bed72f167d7180d1b2708e56
category: bugfix
bugzilla: 44803
CVE: NA

-------------------------------------------------

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.

Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Aristeu Rozanski <aris@ruivo.org>
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>
Link: https://lkml.kernel.org/r/20200922135650.1634-14-osalvador@suse.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
---
 mm/memory-failure.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 148fdd929a19..fa091bfb5943 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1646,6 +1646,9 @@ static int __get_any_page(struct page *p, unsigned long pfn, int flags)
 		} 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);
@@ -1662,6 +1665,9 @@ static int get_any_page(struct page *page, unsigned long pfn, int flags)
 {
 	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)) {
 		/*
-- 
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