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

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Date:	Thu, 11 Jun 2009 11:59:31 -0400
From:	Rik van Riel <riel@...hat.com>
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>,
	"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

Wu Fengguang wrote:
> To avoid possible deadlock. Proposed by Nick Piggin:
> 
>   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
>   type (maybe -rt kernels do it), then you could have a task holding
>   anon_vma lock and waiting for tasklist_lock, and another holding tasklist
>   lock and waiting for i_mmap_lock, and another holding i_mmap_lock and
>   waiting for anon_vma lock.
> 
> CC: Nick Piggin <npiggin@...e.de>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>

Acked-by: Rik van Riel <riel@...hat.com>

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