linux-kernel - Re: [PATCH v1] mm: hugetlb: fix hugepage memory leak caused by wrong reserve count

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Message-ID: <050201d12369$167a0a10$436e1e30$@alibaba-inc.com>
Date:	Fri, 20 Nov 2015 15:57:21 +0800
From:	"Hillf Danton" <hillf.zj@...baba-inc.com>
To:	"'Naoya Horiguchi'" <n-horiguchi@...jp.nec.com>,
	"'Andrew Morton'" <akpm@...ux-foundation.org>
Cc:	"'David Rientjes'" <rientjes@...gle.com>,
	"'Dave Hansen'" <dave.hansen@...el.com>,
	"'Mel Gorman'" <mgorman@...e.de>,
	"'Joonsoo Kim'" <iamjoonsoo.kim@....com>,
	"'Mike Kravetz'" <mike.kravetz@...cle.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>,
	"'Naoya Horiguchi'" <nao.horiguchi@...il.com>
Subject: Re: [PATCH v1] mm: hugetlb: fix hugepage memory leak caused by wrong reserve count

> 
> When dequeue_huge_page_vma() in alloc_huge_page() fails, we fall back to
> 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@...jp.nec.com>
> Cc: <stable@...r.kernel.org> [3.16+]
> ---
> - the reason why I set stable target to "3.16+" is that this patch can be
>   applied easily/automatically on these versions. But this bug seems to be
>   old one, so if you are interested in backporting to older kernels,
>   please let me know.
> ---
>  mm/hugetlb.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git v4.3/mm/hugetlb.c v4.3_patched/mm/hugetlb.c
> index 9cc7734..77c518c 100644
> --- v4.3/mm/hugetlb.c
> +++ v4.3_patched/mm/hugetlb.c
> @@ -1790,7 +1790,10 @@ 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, gbl_chg)) {
> +			SetPagePrivate(page);
> +			h->resv_huge_pages--;
> +		}

I am wondering if this patch was prepared against the next tree.

>  		spin_lock(&hugetlb_lock);
>  		list_move(&page->lru, &h->hugepage_activelist);
>  		/* Fall through */
> --
> 1.7.1

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