[PATCH 4.2.y-ckt 176/305] mm: hugetlb: fix hugepage memory leak caused by wrong reserve count

[Kamal Mostafa]

4.2.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>

commit a88c769548047b21f76fd71e04b6a3300ff17160 upstream.

When dequeue_huge_page_vma() in alloc_huge_page() fails, we fall back on
alloc_buddy_huge_page() to directly create a hugepage from the buddy
allocator.

In that case, however, if alloc_buddy_huge_page() succeeds we don't
decrement h->resv_huge_pages, which means that successful
hugetlb_fault() returns without releasing the reserve count.  As a
result, subsequent hugetlb_fault() might fail despite that there are
still free hugepages.

This patch simply adds decrementing code on that code path.

I reproduced this problem when testing v4.3 kernel in the following situation:
 - the test machine/VM is a NUMA system,
 - hugepage overcommiting is enabled,
 - most of hugepages are allocated and there's only one free hugepage
   which is on node 0 (for example),
 - another program, which calls set_mempolicy(MPOL_BIND) to bind itself to
   node 1, tries to allocate a hugepage,
 - the allocation should fail but the reserve count is still hold.

Signed-off-by: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
Cc: David Rientjes <rientjes at google.com>
Cc: Dave Hansen <dave.hansen at intel.com>
Cc: Mel Gorman <mgorman at suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim at lge.com>
Cc: Hillf Danton <hillf.zj at alibaba-inc.com>
Cc: Mike Kravetz <mike.kravetz at oracle.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
[ luis: backported to 3.16:
  - use 'chg' instead of 'gbl_chg'
  - adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 mm/hugetlb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 62c1ec5..f70850e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1563,7 +1563,10 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
 		if (!page)
 			goto out_uncharge_cgroup;
-
+		if (!avoid_reserve && vma_has_reserves(vma, chg)) {
+			SetPagePrivate(page);
+			h->resv_huge_pages--;
+		}
 		spin_lock(&hugetlb_lock);
 		list_move(&page->lru, &h->hugepage_activelist);
 		/* Fall through */
-- 
1.9.1