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

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Message-ID: <4BBCFE8A.1030602@redhat.com>
Date:	Wed, 07 Apr 2010 17:52:10 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Borislav Petkov <bp@...en8.de>,
	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, hannes@...xchg.org
Subject: Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas
 of a mergeable VMA

On 04/07/2010 05:19 PM, Linus Torvalds wrote:

> Comments?

I remember there being an "unfixable" spot with this
approach when I originally wrote the new anon_vma
linking code.

However, I can't for the life of me find that spot.
I am starting to believe I made it fixable as a side
effect of one of the changes I made :)

One of the issues with your patch is that anon_vma_prepare
can fail and this patch ignores its return value.

Having anon_vma-prepare fail after an mremap or mprotect
might result in messing up the VMAs of a process, or having
to undo the VMA changes that were made.

In fact, this may be the problem I was running into - not
wanting to add even more complex error paths to the vma
shuffling code.
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