linux-kernel - Re: [PATCH 1/3] HWPOISON, hugetlbfs: fix warning on freeing hwpoisoned hugepage

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Date:	Fri,  7 Dec 2012 01:14:42 -0500
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	aneesh.kumar@...ux.vnet.ibm.com
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi.kleen@...el.com>,
	Tony Luck <tony.luck@...el.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/3] HWPOISON, hugetlbfs: fix warning on freeing hwpoisoned hugepage

On Fri, Dec 07, 2012 at 11:06:41AM +0530, Aneesh Kumar K.V wrote:
...
> > From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> > Date: Thu, 6 Dec 2012 20:54:30 -0500
> > Subject: [PATCH v2] HWPOISON, hugetlbfs: fix warning on freeing hwpoisoned
> >  hugepage
> >
> > This patch fixes the warning from __list_del_entry() which is triggered
> > when a process tries to do free_huge_page() for a hwpoisoned hugepage.
> 
> 
> Can you get a dump stack for that. I am confused because the page was
> already in freelist, and we deleted it from the list and set the
> refcount to 1. So how are we reaching free_huge_page() again ?

free_huge_page() can be called for hwpoisoned hugepage from unpoison_memory().
This function gets refcount once and clears PageHWPoison, and then puts
refcount twice to return the hugepage back to free pool.
The second put_page() finally reaches free_huge_page().

Thanks,
Naoya
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