kpageflags: fix wrong KPF_THP on non-huge compound pages
Naoya Horiguchi [Mon, 8 Oct 2012 23:33:47 +0000 (16:33 -0700)]
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@ah.jp.nec.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
Reviewed-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/page.c

index 7fcd0d6..b8730d9 100644 (file)
@@ -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;
 
        /*