linux-kernel - Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon

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Message-ID: <4BC3418D.1050709@redhat.com>
Date:	Mon, 12 Apr 2010 11:51:41 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Borislav Petkov <bp@...en8.de>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	sgunderson@...foot.com
Subject: Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas
 of a mergeable VMA

On 04/12/2010 11:44 AM, Linus Torvalds wrote:
> On Sun, 11 Apr 2010, Rik van Riel wrote:
>>
>> Looking around the code some more, zap_pte_range()
>> calls page_remove_rmap(), which leaves the
>> page->mapping in place and has this comment:
>
> See my earlier email about this exact issue. It's well-known that there
> are stale page->mapping pointers. The "page_mapped()" check _should_ have
> meant that in that case we never follow them, though.

Good point.  I wonder if we have some SMP reordering
issue then?

>> I wonder if we can clear page->mapping here, if
>> list_is_singular(anon_vma->head).  That way we
>> will not leave stale pointers behind.
>
> What does that help? What if list _isn't_ singular?

Yeah, that was a bad idea.  Looking at the same code for
11 days straight seems to have put some knots in my brain :)
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