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    Subject[40/90] mm: hugetlb: fix hugepage memory leak in walk_page_range()
    2.6.31-stable review patch.  If anyone has any objections, please let us know.

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

    From: Naoya Horiguchi <n-horiguchi@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@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>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@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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