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From: Andrew Morton <akpm@linux-foundation.org>
To: "Kenichi Okuyama" <kenichi.okuyama@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [patch] NULL pointer check for vma->vm_mm
Date: Thu, 31 Jan 2008 23:55:44 -0800	[thread overview]
Message-ID: <20080131235544.346b938a.akpm@linux-foundation.org> (raw)
In-Reply-To: <3fd7d7a70801312339p2a142096p83ed286c81379728@mail.gmail.com>

On Fri, 1 Feb 2008 16:39:07 +0900 "Kenichi Okuyama" <kenichi.okuyama@gmail.com> wrote:

> Dear all,
> 
> I was looking at the ./mm/rmap.c .. I found that, in function
> "page_referenced_one()",
>    struct mm_struct *mm = vma->vm_mm;
> was being refererred without NULL check.
> 
> Though I do agree that this works for most of the cases, I thought it
> is better to add
> BUG_ON() for case of mm being NULL.
> 
> attached is the patch for this

If we dereference NULL then the kernel will display basically the same
information as would a BUG, and it takes the same action.  So adding a
BUG_ON here really doesn't gain us anything.

Also, I think vma->vm_mm == 0 is not a valid state, so this just shouldn't
happen - the code is OK to assume that a particular invariant is being
honoured.


  reply	other threads:[~2008-02-01  7:55 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-01  7:39 Kenichi Okuyama
2008-02-01  7:55 ` Andrew Morton [this message]
2008-02-01  8:24   ` Kenichi Okuyama
2008-02-01 10:19     ` Andrew Morton
2008-02-01 17:39       ` Kenichi Okuyama

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