linux-kernel - Re: [PATCH] hugetlb: avoid gratuitous BUG_ON in hugetlb_fault() -> hugetlb

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Date:	Tue, 1 May 2012 21:53:58 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hugetlb: avoid gratuitous BUG_ON in hugetlb_fault() -> hugetlb_cow()

On Mon, Apr 30, 2012 at 3:04 AM, Chris Metcalf <cmetcalf@...era.com> wrote:
> Commit 66aebce747eaf added code to avoid a race condition by
> elevating the page refcount in hugetlb_fault() while calling
> hugetlb_cow().  However, one code path in hugetlb_cow() includes
> an assertion that the page count is 1, whereas it may now also
> have the value 2 in this path.  Consensus is that this BUG_ON
> has served its purpose, so rather than extending it to cover both
> cases, we just remove it.
>
> Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
> ---

Acked-by: Hillf Danton <dhillf@...il.com>

>  mm/hugetlb.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index cd65cb1..baaad5d 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2498,7 +2498,6 @@ retry_avoidcopy:
>                if (outside_reserve) {
>                        BUG_ON(huge_pte_none(pte));
>                        if (unmap_ref_private(mm, vma, old_page, address)) {
> -                               BUG_ON(page_count(old_page) != 1);
>                                BUG_ON(huge_pte_none(pte));
>                                spin_lock(&mm->page_table_lock);
>                                ptep = huge_pte_offset(mm, address & huge_page_mask(h));
> --
> 1.6.5.2
>
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