[PATCH 3.16.y-ckt 042/128] mm: hugetlb: fix hugepage memory leak caused by wrong reserve count

From: Luis Henriques
Date: Sun Jan 24 2016 - 17:31:53 EST

3.16.7-ckt23 -stable review patch. If anyone has any objections, please let me know.


From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>

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

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@xxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[ luis: backported to 3.16:
- use 'chg' instead of 'gbl_chg'
- adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
mm/hugetlb.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f3111955b701..b247049b534a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1398,7 +1398,10 @@ 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--;
+ }
list_move(&page->lru, &h->hugepage_activelist);
/* Fall through */