[ 074/120] kpageflags: fix wrong KPF_THP on non-huge compound pages

[Greg Kroah-Hartman]

3.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>

commit 7a71932d5676b7410ab64d149bad8bde6b0d8632 upstream.

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.

Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Reviewed-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/proc/page.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/fs/proc/page.c
+++ b/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;
 
 	/*


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