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Subject[PATCH] mm hugetlb x86: fix hugepage memory leak in mincore()
Most callers of pmd_none_or_clear_bad() check whether the target
page is in a hugepage or not, but mincore() and walk_page_range()
do not check it. So if we use mincore() on a hugepage on x86 machine,
the hugepage memory is leaked as shown below.
This patch fixes it by extending mincore() system call to support hugepages.

Details
=======
My test program (leak_mincore) works as follows:
- creat() and mmap() a file on hugetlbfs (file size is 200MB == 100 hugepages,)
- read()/write() something on it,
- call mincore() for first ten pages and printf() the values of *vec
- munmap() and unlink() the file on hugetlbfs

Without my patch
----------------
$ cat /proc/meminfo| grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 1000
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ./leak_mincore
vec[0] 0
vec[1] 0
vec[2] 0
vec[3] 0
vec[4] 0
vec[5] 0
vec[6] 0
vec[7] 0
vec[8] 0
vec[9] 0
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 999
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ls /hugetlbfs/
$

Return values in *vec from mincore() are set to 0, while the hugepage
should be in memory, and 1 hugepage is still accounted as used while
there is no file on hugetlbfs.

With my patch
-------------
$ cat /proc/meminfo| grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 1000
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ./leak_mincore
vec[0] 1
vec[1] 1
vec[2] 1
vec[3] 1
vec[4] 1
vec[5] 1
vec[6] 1
vec[7] 1
vec[8] 1
vec[9] 1
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 1000
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ls /hugetlbfs/
$

Return value in *vec set to 1 and no memory leaks.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
---
mm/mincore.c | 34 ++++++++++++++++++++++++++++++++++
1 files changed, 34 insertions(+), 0 deletions(-)

diff --git a/mm/mincore.c b/mm/mincore.c
index 8cb508f..f977e3e 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -14,6 +14,7 @@
#include <linux/syscalls.h>
#include <linux/swap.h>
#include <linux/swapops.h>
+#include <linux/hugetlb.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -72,6 +73,39 @@ static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pag
if (!vma || addr < vma->vm_start)
return -ENOMEM;

+ if (is_vm_hugetlb_page(vma)) {
+ struct hstate *h;
+ unsigned long nr_huge;
+ unsigned char present;
+ i = 0;
+ nr = min(pages, (vma->vm_end - addr) >> PAGE_SHIFT);
+ h = hstate_vma(vma);
+ nr_huge = ((addr + pages * PAGE_SIZE - 1) >> huge_page_shift(h))
+ - (addr >> huge_page_shift(h)) + 1;
+ nr_huge = min(nr_huge,
+ (vma->vm_end - addr) >> huge_page_shift(h));
+ while (1) {
+ /* hugepage always in RAM for now,
+ * but generally it needs to be check */
+ ptep = huge_pte_offset(current->mm,
+ addr & huge_page_mask(h));
+ present = !!(ptep &&
+ !huge_pte_none(huge_ptep_get(ptep)));
+ while (1) {
+ vec[i++] = present;
+ addr += PAGE_SIZE;
+ /* reach buffer limit */
+ if (i == nr)
+ return nr;
+ /* check hugepage border */
+ if (!((addr & ~huge_page_mask(h))
+ >> PAGE_SHIFT))
+ break;
+ }
+ }
+ return nr;
+ }
+
/*
* Calculate how many pages there are left in the last level of the
* PTE array for our address.
--
1.6.0.6



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