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

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Date:	Sat, 10 Apr 2010 13:12:46 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Borislav Petkov <bp@...en8.de>
cc:	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.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 Sat, 10 Apr 2010, Linus Torvalds wrote:
> 
> This patch is scary and untested, but the more I look at that code, the 
> more convinced I am that vma_adjust was _really_ badly screwed up. The 
> patch below may make things worse. I'll test it myself too, but I'm 
> sending it out first, since I was writing the email as I was looking at 
> the piece of cr*p.

Ok, it boots. Which means it must be bug-free and perfect. And I really am 
convinced that the old vma_adjust() use of anon_vma_clone() was _totally_ 
broken, so this really could explain everything.

The RCU grace period thing for the TLB flush does look like a real bug 
too, but it's one that is probably impossible to hit in practice.

A broken vma_adjust(), however, would seem to be trivial to hit once you 
just get the right memory freeing patterns going, because the anon_vma 
would easily be _loong_ gone because we didn't create a chain to it at 
all, so the anon_vma code decided that it's not used any more.

So I'm actually pretty optimistic that this really is it.

		Linus
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