Patch "mm: hugetlb: fix hugepage memory leak caused by wrong reserve count" has been added to the 4.3-stable tree

This is a note to let you know that I've just added the patch titled

mm: hugetlb: fix hugepage memory leak caused by wrong reserve count

to the 4.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-hugetlb-fix-hugepage-memory-leak-caused-by-wrong-reserve-count.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Naoya Horiguchi <[email protected]>
Date: Fri, 11 Dec 2015 13:40:24 -0800
Subject: mm: hugetlb: fix hugepage memory leak caused by wrong reserve count

From: Naoya Horiguchi <[email protected]>

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.

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

@@ -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 */

Patches currently in stable-queue which might be from [email protected] are

queue-4.3/mm-hugetlb-call-huge_pte_alloc-only-if-ptep-is-null.patch queue-4.3/mm-hugetlbfs-fix-bugs-in-fallocate-hole-punch-of-areas-with-holes.patch queue-4.3/mm-hugetlb-fix-hugepage-memory-leak-caused-by-wrong-reserve-count.patch