linux-kernel - Re: [PATCH 2/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeing the wrong VMA information

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Date:	Tue, 27 Apr 2010 09:31:36 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Mel Gorman <mel@....ul.ie>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeing
 the wrong VMA information

On Mon, 26 Apr 2010 20:30:41 -0400
Rik van Riel <riel@...hat.com> wrote:

> On 04/26/2010 06:37 PM, Mel Gorman wrote:
> 
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 85f203e..bc313a6 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1368,15 +1368,31 @@ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
> >   	 * are holding mmap_sem. Users without mmap_sem are required to
> >   	 * take a reference count to prevent the anon_vma disappearing
> >   	 */
> > +retry:
> >   	anon_vma = page_anon_vma(page);
> >   	if (!anon_vma)
> >   		return ret;
> >   	spin_lock(&anon_vma->lock);
> >   	list_for_each_entry(avc,&anon_vma->head, same_anon_vma) {
> >   		struct vm_area_struct *vma = avc->vma;
> > -		unsigned long address = vma_address(page, vma);
> > -		if (address == -EFAULT)
> > -			continue;
> > +		unsigned long address;
> > +
> > +		/*
> > +		 * Guard against deadlocks by not spinning against
> > +		 * vma->anon_vma->lock. If contention is found, release our
> > +		 * lock and try again until VMA list can be traversed without
> > +		 * contention.
> > +		 */
> > +		if (anon_vma != vma->anon_vma) {
> > +			if (!spin_trylock(&vma->anon_vma->lock)) {
> > +				spin_unlock(&anon_vma->lock);
> > +				goto retry;
> > +			}
> > +		}
> 
> If you're part way down the list, surely you'll need to
> unlock multiple anon_vmas here before going to retry?
> 
vma->anon_vma->lock is released after vma_address().

-Kame

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