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Date: Mon, 6 Sep 2010 02:02:27 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
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To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
cc: Kulikov Vasiliy <segooon@gmail.com>, kernel-janitors@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Lee Schermerhorn <lee.schermerhorn@hp.com>,
        Christoph Lameter <cl@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 13/14] mm: mempolicy: Check return code of check_range
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On Mon, 6 Sep 2010, KOSAKI Motohiro wrote:

> > From: Vasiliy Kulikov <segooon@gmail.com>
> > 
> > Function check_range may return ERR_PTR(...). Check for it.
> 
> When happen this issue?
> 
> afaik, check_range return error when following condition.
>  1) mm->mmap->vm_start argument is incorrect
>  2) don't have neigher MPOL_MF_STATS, MPOL_MF_MOVE and MPOL_MF_MOVE_ALL
> 
> I think both case is not happen in real. Am I overlooking anything?
> 

There's no reason not to check the return value of a function when the 
implementation of either could change at any time.  migrate_to_node() is 
certainly not in any fastpath where we can't sacrifice a branch for more 
robust code.