linux-kernel - [PATCH v1] mm: bad_page() checks bad_flags instead of page->flags for hwpoison page

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Message-Id: <1463470975-29972-1-git-send-email-n-horiguchi@ah.jp.nec.com>
Date:	Tue, 17 May 2016 16:42:55 +0900
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: [PATCH v1] mm: bad_page() checks bad_flags instead of page->flags for hwpoison page

There's a race window between checking page->flags and unpoisoning, which
taints kernel with "BUG: Bad page state". That's overkill. It's safer to
use bad_flags to detect hwpoisoned page.

Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
---
 mm/page_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git tmp/mm/page_alloc.c tmp_patched/mm/page_alloc.c
index 5b269bc..4e0fa37 100644
--- tmp/mm/page_alloc.c
+++ tmp_patched/mm/page_alloc.c
@@ -522,8 +522,8 @@ static void bad_page(struct page *page, const char *reason,
 	static unsigned long nr_shown;
 	static unsigned long nr_unshown;
 
-	/* Don't complain about poisoned pages */
-	if (PageHWPoison(page)) {
+	/* Don't complain about hwpoisoned pages */
+	if (bad_flags == __PG_HWPOISON) {
 		page_mapcount_reset(page); /* remove PageBuddy */
 		return;
 	}
-- 
2.7.0