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

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Message-Id: <20121207143414.b2d33095.akpm@linux-foundation.org>
Date:	Fri, 7 Dec 2012 14:34:14 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	aneesh.kumar@...ux.vnet.ibm.com, 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,  7 Dec 2012 10:49:57 -0500
Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:

> 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.

This changelog is very short.  In fact it is too short, resulting in
others having to ask questions about the patch.  When this happens,
please treat it as a sign that the changelog needs additional
information - so that other readers will not feel a need to ask the
same questions!

I added this paragraph:

: 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().

Also, is the description accurate?  Is the __list_del_entry() warning
the only problem?

Or is it the case that this bug will cause memory corruption?  If so
then the patch is pretty important and is probably needed in -stable as
well?  I haven't checked how far back in time the bug exists.

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