[PATCH 3/5] mm: soft-offline: exit with failure for non anonymous thp

[Andrea Righi]

From: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>

Currently memory_failure() doesn't handle non anonymous thp case,
because we can hardly expect the error handling to be successful, and it
can just hit some corner case which results in BUG_ON or something
severe like that.  This is also the case for soft offline code, so let's
make it in the same way.

Orignal code has a MF_COUNT_INCREASED check before put_hwpoison_page(),
but it's unnecessary because get_any_page() is already called when
running on this code, which takes a refcount of the target page
regardress of the flag.  So this patch also removes it.

[akpm at linux-foundation.org: fix build]
Signed-off-by: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
Cc: Andi Kleen <andi at firstfloor.org>
Cc: "Kirill A. Shutemov" <kirill at shutemov.name>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

CVE-2019-10124

(backported from commit 98fd1ef4241ce0c700a174dd3e33c643b4774690)
Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
---
 mm/memory-failure.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 25c4dc2035c9..3730845e349a 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1732,16 +1732,16 @@ static int soft_offline_in_use_page(struct page *page, int flags)
 
 	if (!PageHuge(page) && PageTransHuge(hpage)) {
 		lock_page(hpage);
-		ret = split_huge_page(hpage);
-		unlock_page(hpage);
-		if (unlikely(ret || PageTransCompound(page) ||
-			     !PageAnon(page))) {
-			pr_info("soft offline: %#lx: failed to split THP\n",
-				page_to_pfn(page));
-			if (flags & MF_COUNT_INCREASED)
-				put_hwpoison_page(hpage);
+		if (!PageAnon(hpage) || unlikely(split_huge_page(hpage))) {
+			unlock_page(hpage);
+			if (!PageAnon(hpage))
+				pr_info("soft offline: %#lx: non anonymous thp\n", page_to_pfn(page));
+			else
+				pr_info("soft offline: %#lx: thp split failed\n", page_to_pfn(page));
+			put_hwpoison_page(hpage);
 			return -EBUSY;
 		}
+		unlock_page(hpage);
 		get_hwpoison_page(page);
 		put_hwpoison_page(hpage);
 	}
-- 
2.19.1