linux-kernel - Re: [PATCH 2/5] HWPOISON: fix tasklist_lock/anon

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Message-ID: <20090612100308.GD25568@one.firstfloor.org>
Date:	Fri, 12 Jun 2009 12:03:08 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andi Kleen <andi@...stfloor.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 2/5] HWPOISON: fix tasklist_lock/anon_vma locking order

On Thu, Jun 11, 2009 at 10:22:41PM +0800, Wu Fengguang wrote:
> To avoid possible deadlock. Proposed by Nick Piggin:

I disagree with the description. There's no possible deadlock right now.
It would be purely out of paranoia.

> 
>   You have tasklist_lock(R) nesting outside i_mmap_lock, and inside anon_vma
>   lock. And anon_vma lock nests inside i_mmap_lock.
> 
>   This seems fragile. If rwlocks ever become FIFO or tasklist_lock changes

I was a bit dubious on this reasoning. If rwlocks become FIFO a lot of
stuff will likely break.

>   type (maybe -rt kernels do it), then you could have a task holding

I think they tried but backed off quickly again

It's ok with a less scare-mongering description.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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