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. Signed-off-by: Naoya Horiguchi <[email protected]> Acked-by: KOSAKI Motohiro <[email protected]> Acked-by: David Rientjes <[email protected]> Reviewed-by: Fengguang Wu <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
cbmeeks · Oct 9, 2012 · 7a71932 · 7a71932
1 parent cd8ed2a
commit 7a71932
Showing 1 changed file with 7 additions and 1 deletion.
diff --git 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;
 
 	/*