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From: Greg KH on 16 Dec 2009 20:50
2.6.31-stable review patch. If anyone has any objections, please let us know.

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

From: Naoya Horiguchi <n-horiguchi(a)ah.jp.nec.com>

commit d33b9f45bd24a6391bc05e2b5a13c1b5787ca9c2 upstream.

Most callers of pmd_none_or_clear_bad() check whether the target page is
in a hugepage or not, but walk_page_range() do not check it. So if we
read /proc/pid/pagemap for the hugepage on x86 machine, the hugepage
memory is leaked as shown below. This patch fixes it.

Details
=======
My test program (leak_pagemap) works as follows:
- creat() and mmap() a file on hugetlbfs (file size is 200MB == 100 hugepages,)
- read()/write() something on it,
- call page-types with option -p (walk around the page tables),
- munmap() and unlink() the file on hugetlbfs

Without my patches
------------------
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 1000
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ./leak_pagemap
[snip output]
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 900
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ls /hugetlbfs/
$

100 hugepages are accounted as used while there is no file on hugetlbfs.

With my patches
---------------
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 1000
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ./leak_pagemap
[snip output]
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 1000
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ls /hugetlbfs
$

No memory leaks.

Signed-off-by: Naoya Horiguchi <n-horiguchi(a)ah.jp.nec.com>
Cc: Andi Kleen <ak(a)linux.intel.com>
Cc: Wu Fengguang <fengguang.wu(a)intel.com>
Cc: Hugh Dickins <hugh.dickins(a)tiscali.co.uk>
Cc: Mel Gorman <mel(a)csn.ul.ie>
Cc: Lee Schermerhorn <lee.schermerhorn(a)hp.com>
Cc: Andy Whitcroft <apw(a)canonical.com>
Cc: David Rientjes <rientjes(a)google.com>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
mm/pagewalk.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)

--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -1,6 +1,7 @@
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/sched.h>
+#include <linux/hugetlb.h>

static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
struct mm_walk *walk)
@@ -107,6 +108,7 @@ int walk_page_range(unsigned long addr,
pgd_t *pgd;
unsigned long next;
int err = 0;
+ struct vm_area_struct *vma;

if (addr >= end)
return err;
@@ -117,11 +119,22 @@ int walk_page_range(unsigned long addr,
pgd = pgd_offset(walk->mm, addr);
do {
next = pgd_addr_end(addr, end);
+
+ /* skip hugetlb vma to avoid hugepage PMD being cleared
+ * in pmd_none_or_clear_bad(). */
+ vma = find_vma(walk->mm, addr);
+ if (vma && is_vm_hugetlb_page(vma)) {
+ if (vma->vm_end < next)
+ next = vma->vm_end;
+ continue;
+ }
+
if (pgd_none_or_clear_bad(pgd)) {
if (walk->pte_hole)
err = walk->pte_hole(addr, next, walk);
if (err)
break;
+ pgd++;
continue;
}
if (walk->pgd_entry)
@@ -131,7 +144,8 @@ int walk_page_range(unsigned long addr,
err = walk_pud_range(pgd, addr, next, walk);
if (err)
break;
- } while (pgd++, addr = next, addr != end);
+ pgd++;
+ } while (addr = next, addr != end);

return err;
}


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