linux-kernel - Re: [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon

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Date:	Tue, 25 May 2010 11:01:56 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon_vma()

On Mon, 2010-05-24 at 12:32 -0700, Andrew Morton wrote:
> On Fri, 09 Apr 2010 10:44:53 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Fri, 2010-04-09 at 16:29 +0900, KOSAKI Motohiro wrote:
> > > 
> > > 
> > > diff --git a/mm/rmap.c b/mm/rmap.c
> > > index 8b088f0..b4a0b5b 100644
> > > --- a/mm/rmap.c
> > > +++ b/mm/rmap.c
> > > @@ -295,7 +295,7 @@ struct anon_vma *page_lock_anon_vma(struct page
> > > *page)
> > >         unsigned long anon_mapping;
> > >  
> > >         rcu_read_lock();
> > > -       anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
> > > +       anon_mapping = (unsigned long) rcu_dereference(page->mapping);
> > >         if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
> > >                 goto out;
> > >         if (!page_mapped(page)) 
> > 
> > Yes, I think this is indeed required.
> > 
> > I'll do a new version of the patch that includes the comment updates
> > requested by Andrew.
> 
> Either this didn't happen or I lost the patch.

It didn't happen, I got distracted.

> I parked mm-revalidate-anon_vma-in-page_lock_anon_vma.patch for now. 
> Hopefully everything still works without it..

Yes, I think it actually does due to a number of really non-obvious
things ;-)

I'll try and get back to my make mmu_gather preemptible stuff shortly
and write comments there.
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