linux-kernel - Re: [PATCH] Fix potentially derefencing uninitialized 'r'.

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Date:	Fri, 17 Feb 2012 14:28:06 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Geunsik Lim <geunsik.lim@...il.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Yinghai Lu <yinghai@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] Fix potentially derefencing uninitialized 'r'.

On Fri,  3 Feb 2012 17:20:56 +0900
Geunsik Lim <geunsik.lim@...il.com> wrote:

> struct memblock_region 'r' will not be initialized potentially
> because of while statement's condition in __next_mem_pfn_range()function.
> Initialize struct memblock_region data structure by default.
> 
> Signed-off-by: Geunsik Lim <geunsik.lim@...sung.com>
> ---
>  mm/memblock.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 77b5f22..867f5a2 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -671,7 +671,7 @@ void __init_memblock __next_mem_pfn_range(int *idx, int nid,
>  				unsigned long *out_end_pfn, int *out_nid)
>  {
>  	struct memblock_type *type = &memblock.memory;
> -	struct memblock_region *r;
> +	struct memblock_region *r = &type->regions[*idx];
>  
>  	while (++*idx < type->cnt) {
>  		r = &type->regions[*idx];

The following `if' test prevents any such dereference.

Maybe you saw a compilation warning (I didn't).  If so,
unintialized_var() is one way of suppressing it.

A better way is to reorganise the code (nicely).  Often that option
isn't available.


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