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[PATCH 4.3 027/200] mm: hugetlb: fix hugepage memory leak caused by wrong reserve count

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

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

From: Naoya Horiguchi <n-horiguchi@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@ah.jp.nec.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Mike Kravetz <mike.kravetz@oracle.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@linuxfoundation.org>

---
 mm/hugetlb.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1790,7 +1790,10 @@ struct page *alloc_huge_page(struct vm_a
 		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
 		if (!page)
 			goto out_uncharge_cgroup;
-
+		if (!avoid_reserve && vma_has_reserves(vma, gbl_chg)) {
+			SetPagePrivate(page);
+			h->resv_huge_pages--;
+		}
 		spin_lock(&hugetlb_lock);
 		list_move(&page->lru, &h->hugepage_activelist);
 		/* Fall through */

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[PATCH 4.3 027/200] mm: hugetlb: fix hugepage memory leak caused by wrong reserve count Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-02-15 01:20 +0100

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