linux-kernel - [PATCH v1 3/4] mm/memory-failure: give up error handling for non-tail-refcounted thp

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Message-ID: <1437010894-10262-4-git-send-email-n-horiguchi@ah.jp.nec.com>
Date:	Thu, 16 Jul 2015 01:41:56 +0000
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Andi Kleen <andi@...stfloor.org>, Dean Nelson <dnelson@...hat.com>,
	"Tony Luck" <tony.luck@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	"Hugh Dickins" <hughd@...gle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Naoya Horiguchi" <nao.horiguchi@...il.com>
Subject: [PATCH v1 3/4] mm/memory-failure: give up error handling for
 non-tail-refcounted thp

"non anonymous thp" case is still racy with freeing thp, which causes panic
due to put_page() for refcount-0 page. It seems that closing up this race
might be hard (and/or not worth doing,) so let's give up the error handling
for this case.

Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
---
 mm/memory-failure.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git v4.2-rc2.orig/mm/memory-failure.c v4.2-rc2/mm/memory-failure.c
index f72d2fad0b90..421d7c9b30f4 100644
--- v4.2-rc2.orig/mm/memory-failure.c
+++ v4.2-rc2/mm/memory-failure.c
@@ -909,6 +909,15 @@ int get_hwpoison_page(struct page *page)
 	 * directly for tail pages.
 	 */
 	if (PageTransHuge(head)) {
+		/*
+		 * Non anonymous thp exists only in allocation/free time. We
+		 * can't handle such a case correctly, so let's give it up.
+		 * This should be better than triggering BUG_ON when kernel
+		 * tries to touch a "partially handled" page.
+		 */
+		if (!PageAnon(head))
+			return 0;
+
 		if (get_page_unless_zero(head)) {
 			if (PageTail(page))
 				get_page(page);
@@ -1134,15 +1143,6 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 	}
 
 	if (!PageHuge(p) && PageTransHuge(hpage)) {
-		if (!PageAnon(hpage)) {
-			pr_err("MCE: %#lx: non anonymous thp\n", pfn);
-			if (TestClearPageHWPoison(p))
-				atomic_long_sub(nr_pages, &num_poisoned_pages);
-			put_page(p);
-			if (p != hpage)
-				put_page(hpage);
-			return -EBUSY;
-		}
 		if (unlikely(split_huge_page(hpage))) {
 			pr_err("MCE: %#lx: thp split failed\n", pfn);
 			if (TestClearPageHWPoison(p))
-- 
2.4.3
--
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