linux-kernel - Re: [PATCH] mm: hugetlb: fix non-atomic enqueue of huge page

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Message-Id: <20111226162419.de03469e.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 26 Dec 2011 16:24:19 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>, stable@...nel.org
Subject: Re: [PATCH] mm: hugetlb: fix non-atomic enqueue of huge page

On Fri, 23 Dec 2011 21:35:25 +0800
Hillf Danton <dhillf@...il.com> wrote:

> From: Hillf Danton <dhillf@...il.com>
> Subject: [PATCH] mm: hugetlb: fix non-atomic enqueue of huge page
> 
> If huge page is enqueued under the protection of hugetlb_lock, then
> the operation is atomic and safe.
> 
> Cc: Michal Hocko <mhocko@...e.cz>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Hillf Danton <dhillf@...il.com>

Hmm, at reporting this kind of bug...it's better to show when it's broken.
Maybe this commit a9869b837c098732bad84939015c0eb391b23e41
and it's better to cc stable.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

> ---
> 
> --- a/mm/hugetlb.c	Tue Dec 20 21:26:30 2011
> +++ b/mm/hugetlb.c	Fri Dec 23 21:16:28 2011
> @@ -901,7 +901,6 @@ retry:
>  	h->resv_huge_pages += delta;
>  	ret = 0;
> 
> -	spin_unlock(&hugetlb_lock);
>  	/* Free the needed pages to the hugetlb pool */
>  	list_for_each_entry_safe(page, tmp, &surplus_list, lru) {
>  		if ((--needed) < 0)
> @@ -915,6 +914,7 @@ retry:
>  		VM_BUG_ON(page_count(page));
>  		enqueue_huge_page(h, page);
>  	}
> +	spin_unlock(&hugetlb_lock);
> 
>  	/* Free unnecessary surplus pages to the buddy allocator */
>  free:
> --
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