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Date: Mon, 5 Jan 2009 13:03:18 +0300
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Andrew Morton <akpm@linux-foundation.org>, Nick Piggin <npiggin@suse.de>,
       Rik van Riel <riel@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
       Jiri Slaby <jirislaby@gmail.com>
Subject: Re: [PATCH] mm: __nr_to_section - make it safe against overflow
Message-ID: <20090105100318.GC7645@localhost>
References: <20090105094034.GA7645@localhost> <84144f020901050200h3fd6ce71qacd5e2dff282a9@mail.gmail.com>
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[Pekka Enberg - Mon, Jan 05, 2009 at 12:00:58PM +0200]
| Hi Cyrill,
| 
| On Mon, Jan 5, 2009 at 11:40 AM, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
| > @@ -980,9 +986,12 @@ extern struct mem_section mem_section[NR
| >
| >  static inline struct mem_section *__nr_to_section(unsigned long nr)
| >  {
| > -       if (!mem_section[SECTION_NR_TO_ROOT(nr)])
| > +       unsigned long idx = SECTION_NR_TO_ROOT(nr);
| > +       WARN_ON_ONCE(idx >= NR_SECTION_ROOTS);
| > +
| > +       if (idx >=NR_SECTION_ROOTS || !mem_section[idx])
| >                return NULL;
| 
| Looks good to me but I have minor nitpick. You might want to write the
| above like this:
| 
|     if (WARN_ON_ONCE(idx >= NR_SECTION_ROOTS))
|             return NULL;
| 
| to separate the error condition from the normal case where we don't
| have a mem section.
| 
| > -       return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
| > +       return &mem_section[idx][nr & SECTION_ROOT_MASK];
| >  }
| 

Hi Pekka,

thanks, indeed! I forget that WARN_.. do return a value :)
Will fix shortly.

		- Cyrill -