mm: hugetlb: fix hugepage memory leak in walk_page_range()

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@ah.jp.nec.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: David Rientjes <rientjes@google.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index d5878bed7841..a286915e23ef 100644
--- 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, unsigned long end,
         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, unsigned long end,
         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, unsigned long end,
                         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;
 }