releases/3.6.2/kpageflags-fix-wrong-kpf_thp-on-non-huge-compound-pages.patch

   1 From 7a71932d5676b7410ab64d149bad8bde6b0d8632 Mon Sep 17 00:00:00 2001
   2 From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
   3 Date: Mon, 8 Oct 2012 16:33:47 -0700
   4 Subject: kpageflags: fix wrong KPF_THP on non-huge compound pages
   5
   6 From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
   7
   8 commit 7a71932d5676b7410ab64d149bad8bde6b0d8632 upstream.
   9
  10 KPF_THP can be set on non-huge compound pages (like slab pages or pages
  11 allocated by drivers with __GFP_COMP) because PageTransCompound only
  12 checks PG_head and PG_tail.  Obviously this is a bug and breaks user space
  13 applications which look for thp via /proc/kpageflags.
  14
  15 This patch rules out setting KPF_THP wrongly by additionally checking
  16 PageLRU on the head pages.
  17
  18 Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
  19 Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
  20 Acked-by: David Rientjes <rientjes@google.com>
  21 Reviewed-by: Fengguang Wu <fengguang.wu@intel.com>
  22 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  23 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  24 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  25
  26 ---
  27  fs/proc/page.c |    8 +++++++-
  28  1 file changed, 7 insertions(+), 1 deletion(-)
  29
  30 --- a/fs/proc/page.c
  31 +++ b/fs/proc/page.c
  32 @@ -115,7 +115,13 @@ u64 stable_page_flags(struct page *page)
  33                 u |= 1 << KPF_COMPOUND_TAIL;
  34         if (PageHuge(page))
  35                 u |= 1 << KPF_HUGE;
  36 -       else if (PageTransCompound(page))
  37 +       /*
  38 +        * PageTransCompound can be true for non-huge compound pages (slab
  39 +        * pages or pages allocated by drivers with __GFP_COMP) because it
  40 +        * just checks PG_head/PG_tail, so we need to check PageLRU to make
  41 +        * sure a given page is a thp, not a non-huge compound page.
  42 +        */
  43 +       else if (PageTransCompound(page) && PageLRU(compound_trans_head(page)))
  44                 u |= 1 << KPF_THP;
  45
  46         /*