linux-kernel - Re: [ 04/26] hugetlbfs: add swap entry check in follow_hugetlb

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Date:	Fri, 26 Apr 2013 07:38:46 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Ben Hutchings <ben@...adent.org.uk>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Michal Hocko <mhocko@...e.cz>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [ 04/26] hugetlbfs: add swap entry check in follow_hugetlb_page()

On Wed, Apr 24, 2013 at 04:23:29PM -0700, Greg Kroah-Hartman wrote:
> On Thu, Apr 25, 2013 at 12:04:10AM +0100, Ben Hutchings wrote:
> > On Tue, Apr 23, 2013 at 02:53:44PM -0700, Greg Kroah-Hartman wrote:
> > > 3.4-stable review patch.  If anyone has any objections, please let me know.
> > > 
> > > ------------------
> > > 
> > > From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> > > 
> > > commit 9cc3a5bd40067b9a0fbd49199d0780463fc2140f upstream.
> > > 
> > > With applying the previous patch "hugetlbfs: stop setting VM_DONTDUMP in
> > > initializing vma(VM_HUGETLB)" to reenable hugepage coredump, if a memory
> > > error happens on a hugepage and the affected processes try to access the
> > > error hugepage, we hit VM_BUG_ON(atomic_read(&page->_count) <= 0) in
> > > get_page().
> >  
> > Is this required?  You didn't apply the previous patch referred to
> > above (commit a2fce9143057) to 3.4.y or 3.0.y since it claimed to fix
> > a regression in 3.7 (commit 314e51b9851b 'mm: kill vma flag VM_RESERVED
> > and mm->reserved_vm counter').
> > 
> > I'm not saying it *isn't* required, mind.
> 
> Yeah, but I went off of the stable: marking in this patch, which said:
> 	    Cc: <stable@...r.kernel.org>        [2.6.34+?]
> 
> 
> Naoya, any chance you could clear this up?  Is this needed for kernels
> older than 3.7?

Hi Greg,

Kernels older than 3.7 need this patch.

We need this patch whenever hugepage coredump is enabled.
It was enabled before commit 314e51b9851b (== v3.6-8946-g314e51b),
but the commit disabled it accidentally, so commit a2fce914305
(== v3.9-rc7-56-ga2fce91) reenabled it.

Thanks,
Naoya
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