linux-kernel - [PATCH v4] kpageflags: fix wrong KPF

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Date:	Wed, 26 Sep 2012 16:27:14 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Andi Kleen <andi.kleen@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v4] kpageflags: fix wrong KPF_THP on non-huge compound pages

KPF_THP can be set on non-huge compound pages (like slab pages or pages
allocated by drivers with __GFP_COMP) because PageTransCompound only
checks PG_head and PG_tail. Obviously this is a bug and breaks user space
applications which look for thp via /proc/kpageflags.

This patch rules out setting KPF_THP wrongly by additionally checking
PageLRU on the head pages.

Changelog in v4:
  - check PageLRU with compound_trans_head()
  - fix patch subject again

Changelog in v3:
  - check PageSlab instead of PageAnon
  - fix patch subject

Changelog in v2:
  - add a comment in code

Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Acked-by: David Rientjes <rientjes@...gle.com>
---
 fs/proc/page.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git v3.6-rc6.orig/fs/proc/page.c v3.6-rc6/fs/proc/page.c
index 7fcd0d6..b8730d9 100644
--- v3.6-rc6.orig/fs/proc/page.c
+++ v3.6-rc6/fs/proc/page.c
@@ -115,7 +115,13 @@ u64 stable_page_flags(struct page *page)
 		u |= 1 << KPF_COMPOUND_TAIL;
 	if (PageHuge(page))
 		u |= 1 << KPF_HUGE;
-	else if (PageTransCompound(page))
+	/*
+	 * PageTransCompound can be true for non-huge compound pages (slab
+	 * pages or pages allocated by drivers with __GFP_COMP) because it
+	 * just checks PG_head/PG_tail, so we need to check PageLRU to make
+	 * sure a given page is a thp, not a non-huge compound page.
+	 */
+	else if (PageTransCompound(page) && PageLRU(compound_trans_head(page)))
 		u |= 1 << KPF_THP;
 
 	/*
-- 
1.7.11.4

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